Le clans des mouettes

ainsi est la force.
 
AccueilAccueil  FAQFAQ  RechercherRechercher  S'enregistrerS'enregistrer  MembresMembres  GroupesGroupes  Connexion  

Partagez | 
 

 The Search for Life and Exoplanets, Solar System and Beyond.

Voir le sujet précédent Voir le sujet suivant Aller en bas 
AuteurMessage
yanis la chouette



Nombre de messages : 7780
Localisation : http://yanis.tignard.free.fr/
Date d'inscription : 09/11/2005

MessageSujet: The Search for Life and Exoplanets, Solar System and Beyond.   Ven 17 Nov à 9:44

Solar System and Beyond.
https://www.nasa.gov/topics/solarsystem/index.html
depuis plus de quarante ans, les banques furent septique sur ce sujet
et si il y avait pas eu les rouges, on en serai encore à discuter sur la métaphore de
la caverne de Platon.
NIETZSCHE.
TAY

" C'ÉTAIT COMMENT LE MONDE AVANT L'EXTINCTION DES ABEILLES..." DEMANDE L'ENFANT.
" UN MONDE DANS LEQUEL NOUS N'AVONS PAS PRIS CONSCIENCE
DE VOIR LA FRAGILITÉ DES ACTES SIMPLE DE L'EXISTENCE:
SAVOURER LES ODEURS SIMPLES DE LA VIE.": RÉPOND LE VIEIL HOMME...

UNE INTRODUCTION SUR LES NOUVELLES AVENTURES DE XENA LA GUERRIÈRE ET DE GABRIELLE L'AMAZONE...
https://www.facebook.com/EpochTimesParis/?hc_ref=ARQnUhBdLnjmCErgx6nHBbj7GsYcjRxPKRo-1oPgcIEh29kyIDyabcrZYxDjJ_4kKXs&fref=nf&pnref=story

REMARQUES DE
TAY La chouette effraie.

What’s a Supermoon and Just How Super Is It?
By Lyle Tavernier

The term “supermoon” has been popping up a lot in the news and on social media over the past few years. But what are supermoons, why do they occur and how can they be used as an educational tool. Plus, are they really that super?

There’s a good chance you’ll hear even more about supermoons in the coming months. The full moon on December 3 marks the first and only supermoon of 2017, but it will be followed by two more in January and February 2018. Three supermoons in a row! Now is a great time to learn about these celestial events and get students exploring more about Earth’s only natural satellite.
Moon and Supermoon Lessons from NASA/JPL Edu
Lessons About the Moon

Explore our collection of standards-aligned lessons for grades 1-12.
How it Works

As the Moon orbits Earth, it goes through phases, which are determined by its position relative to Earth and the Sun. When the Moon lines up on the opposite side of Earth from the Sun, we see a full moon. The new moon phase occurs when the Moon and the Sun are lined up on the same side of Earth.

The Moon doesn’t orbit in a perfect circle. Instead, it travels in an ellipse that brings the Moon closer to and farther from Earth in its orbit. The farthest point in this ellipse is called the apogee and is about 405,500 kilometers from Earth on average. Its closest point is the perigee, which is an average distance of about 363,300 kilometers from Earth. During every 27-day orbit around Earth, the Moon reaches both its apogee and perigee.

Full moons can occur at any point along the Moon’s elliptical path, but when a full moon occurs at or near the perigee, it looks slightly larger and brighter than a typical full moon. That’s what the term “supermoon" refers to.

What makes a supermoon super? Watch this short animation to find out. Credit: NASA/JPL-Caltech

Because supermoon is not an official astronomical term, there is no definition about just how close to perigee the full moon has to be in order to be called “super." Generally, supermoon is used to refer to a full moon 90 percent or closer to perigee. (When the term supermoon was originally coined, it was also used to describe a new moon in the same position, but since the new moon isn’t easily visible from Earth, it’s rarely used in that context anymore.)

A more accurate and scientific term is “perigee syzygy.” Syzygy is the alignment of three celestial bodies, in this case the Sun, Moon and Earth. But that doesn’t quite roll off the tongue as easily as supermoon.
Why It’s Important

As the largest and brightest object in the night sky, the Moon is a popular focal point for many amateur and professional astronomers pointing their telescopes to the sky, and the source of inspiration for everyone from aspiring space scientists to engineers to artists.

The supermoon is a great opportunity for teachers to connect concepts being taught in the classroom to something students will undoubtedly be hearing about. Students can practice writing skills in a Moon journal, study Moon phases and apply their math skills to observing the supermoon. (Click here for related activities from JPL’s Education Office.)

Incorrect and misleading information about the Moon (and supermoons) can lead to confusion and frustration. It’s important to help students understand what to expect and be able to identify inaccurate info.
What to Expect
Size

As with anything that moves closer to the person viewing it, the supermoon will appear bigger than an average full Moon. At its largest, it can appear 14% larger in diameter than the smallest full moon. Keep in mind that a 14% increase in the apparent size of something that can be covered with a fingernail on an outstretched arm won’t seem significantly bigger. Unlike side-by-side comparisons made in science and everyday life, students will not have seen the full moon for at least 30 days, and won’t see another for at least 30 more days. Comparing a supermoon with a typical full moon from memory is very difficult.

A nearly full Moon sets as the space shuttle Discovery sits atop Launch pad 39A at the Kennedy Space Center in Cape Canaveral, Florida, Wednesday, March 11, 2009. Photo Credit: (NASA/Bill Ingalls

While they make for great photographs, images like this one that rely on a special photographic technique aren't an accurate representation of what the supermoon will look like to the naked eye. Credit: NASA/Bill Ingalls | Full image and caption on Flickr
Graphic showing the position of the moon at apogee and perigee

A supermoon looks bigger than a "micromoon" (when the full moon is at apogee) because it's about 40,000 kilometers closer to Earth on average. Credit: NASA/JPL-Caltech
Graphic showing the position of the moon at apogee and perigee

It's nearly impossible to compare the apparent size of the supermoon with a micromoon from memory, but when seen side-by-side as in this graphic, it becomes clear. Credit: NASA/JPL-Caltech

Leading up to a supermoon, there are often misleading images on popular media. A technique that involves using a long telephoto lens to take photographs of the Moon next to buildings or other objects makes the Moon look huge compared with its surroundings. This effect can make for great photographs, but it has nothing to do with the supermoon. In fact, these photos can be taken during any Moon phase, but they will likely be used in stories promoting the supermoon.

There are also images that have been edited to inaccurately dramatize the size of the supermoon. Both of these can lead students, and adults, taking pictures with their cell phone to think that they’ve done something wrong or just aren’t cut out for observing the sky, which isn’t true!

Your students may have noticed that when they see a full moon low on the horizon, it appears huge and then seems to shrink as it rises into the night sky. This can happen during any full moon. Known as the Moon Illusion, it has nothing to do with a supermoon. In fact, scientists still aren’t sure what causes the Moon Illusion.
Brightness

The full moon is bright and the supermoon is even brighter! Sunlight reflecting off the Moon during its full phase is bright enough to cast shadows on the ground. During a supermoon, that brightness can increase up to 30 percent as a result of the Moon being closer to Earth, a phenomenon explained by the inverse square law. (Introduce students to the inverse square law with this space-related math lesson for 6th- through 8th-graders.) As with the size of the Moon, students may not remember just how bright the last full moon was or easily be able to compare it. Powerful city lights can also diminish how bright a supermoon seems. Viewing it away from bright overhead street lights or outside the city can help viewers appreciate the increase in brightness.
What Not to Expect

A supermoon will not cause extreme flooding, earthquakes, fires, volcanic eruptions, severe weather, nor tsunamis, despite what incorrect and non-scientific speculators might suggest. Encourage your students to be good scientists and research this for themselves.
Teach It

The excitement and buzz surrounding a supermoon is a great opportunity to teach a variety of Moon topics with these lessons from JPL’s Education Office:

   *NEW* Observing the Moon (Grades K-6) – Students identify the Moon’s location in the sky and record their observations over the course of the Moon-phase cycle in a journal.
   *NEW* Measuring the Supermoon (Grades 5-12) – Students take measurements of the Moon during its full phases over multiple Moon cycles to compare and contrast results.
   Moon Phases (Grades 1-6) – Students learn about the phases of the Moon by acting them out. In 30 minutes, they will act out one complete Moon cycle.
   Whip Up a Moon-Like Crater (Grades 1-6) – Whip up a Moon-like crater with baking ingredients as a demonstration for students.
   Modeling the Earth-Moon System (Grades 6-Cool – Using an assortment of playground and toy balls, students will measure diameter, calculate distance and scale, and build a model of the Earth-Moon system.

TAGS: Supermoon, Moon Phases, Moon, Earth's Moon, What's Up, Astronomy, K-12, Educators

   Lyle Tavernier
   ABOUT THE AUTHOR

   Lyle Tavernier, Educational Technology Specialist, NASA/JPL Edu

   Lyle Tavernier is an educational technology specialist at NASA's Jet Propulsion Laboratory. When he’s not busy working in the areas of distance learning and instructional technology, you might find him running with his dog, cooking or planning his next trip.

https://www.jpl.nasa.gov/edu/news/2017/11/15/whats-a-supermoon-and-just-how-super-is-it/
Revenir en haut Aller en bas
Voir le profil de l'utilisateur http://www.atelier-yannistignard.com
yanis la chouette



Nombre de messages : 7780
Localisation : http://yanis.tignard.free.fr/
Date d'inscription : 09/11/2005

MessageSujet: Re: The Search for Life and Exoplanets, Solar System and Beyond.   Ven 17 Nov à 9:50

The Search for Life and Exoplanets...

Copernicus System
Edit
Comments
Share
Exoplanetary Scratchpad

[SysBP Img]
Copernicus is also known as Rho Cancri, 55 Cancri, Rho1 Cancri, HR 3522, Gl 324, and HD 75732. Wide binary star consisting of a sun-like primary (A, though super metal rich) and a red-dwarf secondary (B) separated by 1,100 AU, 41 light years away. Star A contains five exoplanets, the first system found with four or five planets. It has three tightly packed eccentric planets close in to the star, including planet Jannsen (e, hot Super Earth/Neptunian), Galileo (b, warm Jupiter), and Brahe (c, hot Saturn), followed by an eccentric Saturn in the habitable zone (Harriot, f) and a Jupiter analog, Lippershey (d). Planet e was heralded as the first Neptunian discovered. It was later found to be the shortest-period planet discovered (18 hours) and to transit. Its density was measured and determined to be rocky, and thus re-dubbed the first Super-Earth discovered. It was then the first super-Earth to have its light detected (by Spitzer in the infrared). The planet has about half of Neptune's mass, but is Earth-like in size and density (2.17 Earth Radius). Studies taking into account the composition of the star suggested that it was largely made of diamond, with graphite at the surface (the first diamond planet around a Sunlike star), and the first terrestrial found with fundamentally different surface composition and processes than Earth. This was later refuted when it turned out there wasn't as much carbon in the parent star as believed. Earlier studies that assumed an Earth-like composition suggested that it would be covered with an ocean of super-critical water. The brightness of the planet was found to have raised dramatically, possibly the aftermath of cloud cover due to a volcanic eruption. The brightness of the star (also closest known to transit and only known naked eye star to do so) makes it more easily studied than other hot super Earths. It was found to be dark and its sun-facing side hot enough to melt metal. It became the first super Earth to have its atmospheric composition measured (mostly hydrogen and helium with hints of hydrogen cyanide which would only dominate in a carbon-rich environment and no traces of water vapor) and temperature mapped, and the large hemispherical temperature differences suggest little atmosphere to transport heat. Planet b (one of the original 4 Hot Jupiters discovered) is the first "warm Jupiter" found to have a puffed up atmosphere and it probably at the outer limit from the star at which a planet can lose its atmosphere in this way. Its outer atmosphere skims the surface of the star, which was detected when attempting to detect an atmosphere around transiting Janssen. The strong interaction between planets Galileo and Brahe can be detected in measurements, and it took a while to find a fit that would allow them to survive over long periods of time. Harriot is a very eccentric Saturnian in the habitable zone. Planet d is a super jovian at Jupiter-like distances, which was the first found at true Jupiter distances and still the exoplanet discovered with dopplar spectrometry with the largest known semi-major axis. It was first thought to be circular, then eccentric, and then circular again. The distant outer star causes Lippershey's axis to flip on its axis every million years. Lippershey in turn causes the other planets to flip, including its star. The axis tilt of transiting planet e should be determined at some point. "Bode's law" predicts four undiscovered planets. One of the first 20 exoplanet systems allowed to be given common names by the IAU.



Note: Old Description for planet e: Planet e was the first Neptunian discovered. It was later found to be the shortest-period planet discovered (18 hours) and to transit. The planet has about half of Neptune's mass, but is Earth-like in size and density (2.17 Earth Radius). It is composed 70% of rock and the outer 30% is likely an ocean of super-critical water (between a gas and liquid state) that is 3000km thick. This is the hottest and densest super-Earth and the is the most watery planet found to date. It likely possesses a thick atmosphere of CO and CO2. The brightness of the star (also closest known to transit and only known naked eye star to do so) makes it more easily studied than other hot super Earths.

AINSI,

News | November 16, 2017
NASA Survey Technique Estimates Congo Forest's Carbon

The equivalent of 85 billion tons of carbon dioxide -- a huge amount equal to three-quarters of the carbon stored in forests across the contiguous United States -- is locked in the living vegetation of one African country that holds much of the second largest tropical rainforest in the world, according to new research.

The study conducted by NASA, UCLA and the World Wide Fund for Nature-Germany produced the first high-resolution map of the amount and distribution of carbon stored in the Democratic Republic of Congo (DRC). DRC is the largest country in the Congo Basin and home to a massive and largely inaccessible rainforest that is Earth's second largest reservoir of carbon in vegetation, second only to the Amazon Basin rainforest. The DRC's forests cover an area four times the size of California.

The DRC carbon stock estimates are based on very fine-scale three-dimensional measurements of forest structure that provide, for the first time, data for one of the most diverse tropical forests on Earth. The measurements will help scientists understand the role of this forest in the global carbon cycle and how variations in climate may influence their carbon stock and function.

"We learned that the distribution of carbon in the above-ground biomass of the more than 150 million hectares (about 371 million acres) of forest in the DRC is extremely variable and diverse because of the region's climate, soil types, and a long history of human presence," said Sassan Saatchi, a senior researcher at NASA's Jet Propulsion Laboratory in Pasadena, California, who led the research team. "You cannot think of the Congo rainforest as this big green carpet anymore. We encountered a large variety of tree sizes and densities across the DRC, producing extremely complex regional patterns of carbon stored in the forest."

Traditionally, inventories of forest carbon and biomass are done by researchers who hike into the forest and set up plots on the ground that attempt to capture the full range of terrain. These data are then catalogued, measured and revisited in the future to see how they've changed. The Congo Basin forests, however, span five countries, and many areas are difficult to access due to the lack of infrastructure and rough terrain, which doesn't allow for comprehensive ground measurements of the forest carbon. To observe the forests, the research team took to both air and space.

Using the same forestry techniques to establish inventory plots on the ground, the research team contracted a local African company to fly an airplane outfitted with a commercial Light Detection and Ranging (LIDAR) instrument over 216 locations covering more than 2.5 million acres (half a million hectares) of tropical forest. At each location, the LIDAR captured the height, canopy profile, and outline of treetop canopies with data points 20 inches (50 centimeters) apart, from which they derived the forest structure and carbon estimate. These data were paired with data from NASA's Shuttle Radar Topography Mission, which provided the slopes and curves of the ground surface itself; Japan Aerospace Exploration Agency Advanced Land Observing Satellite Phased Array type L-band Synthetic Aperture Radar (PALSAR) data; and U.S. Geological Survey-NASA Landsat vegetation observations. The combined data sets were scaled up to produce a map of the entire above-ground forest carbon stocks for each 12,000-square-yard (1-hectare) land unit.

Conserving tropical forests like the Congo is a high priority for the United Nations in its efforts to defray the effects of climate change. The U.N. has a policy initiative known as Reduce Emissions from Deforestation and Degradation (REDD+) in nations with large forests like the DRC. The new findings and research methods, conducted in partnership with scientists and the DRC government, are the first step for DRC to establish a baseline assessment of its carbon stocks and a system for future forest monitoring required to participate in REDD+ and be eligible for compensation for preserving the forests.

Saatchi says preserving forests is probably the most immediate mechanism we have to mitigate carbon dioxide accumulating in the atmosphere. A quarter of the entire amount of carbon that goes into the atmosphere globally is absorbed by Earth's vegetation, so protecting and possibly increasing the amount of carbon stored in forests could have significant benefits, such as mitigating climate change and preserving biodiversity and water quality.

"The DRC national carbon map is a truly significant contribution to DRC's future sustainable development," said co-author Aurélie Shapiro at World Wide Fund for Nature-Germany in Berlin. "This innovative product demonstrates with unprecedented accuracy the important role of Congolese forests in mitigating climate change, which is facilitating investments into emissions reductions programs."

To estimate the carbon stored above ground in DRC forests, the research team developed data sets for tree height and tree cover, which vary from one end of the DRC to the other. This information is also extremely helpful to conservationists interested in quantifying the health of habitats for gorillas and other at-risk animals, said Shapiro.

The new results will help test and validate the capabilities of two upcoming NASA missions: the NASA-Indian Space Research Organization Synthetic Aperture Radar, or NISAR, mission, managed by JPL; and the LIDAR observations from the Global Ecosystem Dynamics Investigation, or GEDI, mission, managed by NASA's Goddard Space Flight Center in Greenbelt, Maryland. GEDI will mount a space-based LIDAR on the International Space Station to produce high-resolution 3-D imagery of Earth's forests.

The study is published Nov. 8 in Scientific Reports, a Nature publication. The paper is at:

www.nature.com/articles/s41598-017-15050-z

News Media Contact
Alan Buis
Jet Propulsion Laboratory, Pasadena, California
818-354-0474
Alan.Buis@jpl.nasa.gov

Written by Ellen Gray
NASA's Earth Science News Team

2017-297

https://www.jpl.nasa.gov/news/news.php?feature=7002&utm_source=iContact&utm_medium=email&utm_campaign=NASAJPL&utm_content=earth20171116
https://www.nasa.gov/topics/solarsystem/index.html

RAPPORT DE
Y'BECCA
Revenir en haut Aller en bas
Voir le profil de l'utilisateur http://www.atelier-yannistignard.com
yanis la chouette



Nombre de messages : 7780
Localisation : http://yanis.tignard.free.fr/
Date d'inscription : 09/11/2005

MessageSujet: Re: The Search for Life and Exoplanets, Solar System and Beyond.   Ven 17 Nov à 9:52

Earth from Space
European Space Agency sent this email alert on 17-11-2017 10:20 AM CET

Earth from Space
16-11-2017 12:29 PM CET

https://content.govdelivery.com/accounts/EUESA/bulletins/1c58175

In the 248th edition, discover Chile’s largest salt flat in the Atacama Desert

Flying hundreds of kilometers above the Earth, satellites rarely see the human suffering from war and poverty. But decades of unrest have left a very visible impact on the Democratic Republic of the Congo (DRC).

The DRC contains half of Africa’s tropical forest and the second largest continuous tropical forest in the world. Because of unrest and economic instability, the Democratic Republic of the Congo has mostly escaped the industrial-scale deforestation that has taken place in other tropical countries such as Brazil and Indonesia. The exception is near the country’s eastern border, around Virunga National Park.

Home to critically endangered mountain gorillas, the forests have been disappearing quickly as population growth and violence have driven people into the resource-rich forest in and around the park. Subsistence slash-and-burn agriculture and charcoal production have eaten away at the trees, transforming deep green forests into pale savanna grasslands.

The Landsat 5 satellite obtained the top image on February 13, 1999, and the lower image on September 1, 2008. (More recent images of the region were cloudy.) The city of Beni is tan and gray, while the forested Virunga National Park is dark green. The blue Semlike River meanders northeast through the park. The rate of forest loss shown in these two images is the highest among all national parks in the country.

As a whole, the Democratic Republic of the Congo contains 159,529,000 hectares (615,942 square miles) of forest. Between 2000 and 2010, the country lost 3,711,800 hectares (14,331 square miles) of it, according to a recent analysis of Landsat data completed by Peter Potapov and a team of researchers from South Dakota State University, the University of Maryland, and the Observatoire Satellital des Forêts d’Afrique Centrale. The study by Potapov is the first to survey the entire country since the U.S. Geological Survey made Landsat data available for free in 2008.

Understanding tropical deforestation is important because forests store vast amounts of carbon. Deforestation releases carbon to the atmosphere and prevents the forest from taking up more carbon. Tropical forests also sustain a wide array of plants and animals.

References
Democratic Republic of the Congo (2011) Verunga National Park. Accessed September 10, 2012.
NASA Goddard Space Flight Center (2012, June 18) Mapping the future with Landsat. Accessed September 10, 2012.
Potapov, P.V., Turubanova, S.A., Hansen, M.C., Adusei, B., Broich, M., Altstatt, A., Mane, L., and Justice, C.O. (2012, July) Quantifying forest cover loss in Democratic Republic of the Congo, 2000-2010, with Landsat ETM+ data. Remote Sensing of Environment, 122, 106-116.

NASA Earth Observatory images by Jesse Allen and Robert Simmon, using Landsat data from the USGS Global Visualization Viewer and park boundary data from Protected Planet. Caption by Holli Riebeek.

Instrument(s):
Landsat 5 - TM

https://earthobservatory.nasa.gov/IOTD/view.php?id=79276

RAPPORT DE
Y'BECCA
SOUS LE REGARD DU
CITOYEN TIGNARD YANIS
Revenir en haut Aller en bas
Voir le profil de l'utilisateur http://www.atelier-yannistignard.com
yanis la chouette



Nombre de messages : 7780
Localisation : http://yanis.tignard.free.fr/
Date d'inscription : 09/11/2005

MessageSujet: Re: The Search for Life and Exoplanets, Solar System and Beyond.   Ven 17 Nov à 10:01

National Aeronautics and Space
Administration Page Last Updated:
Aug. 4, 2017 Page
Editor: Lynn Jenner NASA Official: Brian Dunbar

https://www.nasa.gov/mission_pages/landsat/main/index.html


Landsat Sets the Standard for Maps of World's Forests
06.18.12

NASA's Earth-observing fleet of satellites provides a worldwide and unbiased view with standardized scientific data -- information crucial for tracking the health of the world's forests.

Countries like Brazil are using data from NASA satellites to track and measure their forests in advance of a United Nations effort to reduce climate change by providing "carbon credits" for protected land.

The concept is known as REDD+, which stands for Reducing Emissions from Deforestation and Forest Degradation. It includes monitoring forest degradation and efforts in conservation and sustainable management.

"REDD+ aims to make forests more valuable standing than they would be cut down, by creating a financial value for the carbon stored in trees," says Yemi Katerere, head of the United Nations' UN-REDD Programme Secretariat in Geneva, Switzerland. "It creates an incentive for developing countries to reduce carbon emissions by protecting, better managing and wisely using their forest resources, contributing to the global fight against climate change."

REDD+ will be a major topic of discussion during this week's Conference on Sustainable Development, known as Rio+20. Images and data acquired by Landsat satellites are increasingly becoming an accepted approach for anyone hoping to have a long-term view of the health of the world's forests.

"For example Brazil is using Landsat data from 1996 to 2005 to create a baseline for tracking future forest coverage," says Doug Morton, a NASA Landsat researcher at the NASA's Goddard Space Flight Center in Greenbelt, Md.

https://www.nasa.gov/mission_pages/landsat/news/forest-maps.html

Landsat 8 consist of two major segments: the observatory and the ground system. The observatory consists of the spacecraft bus and its payload of two Earth observing sensors, the Operational Land Imager (OLI) and the Thermal Infrared Sensor (TIRS). OLI and TIRS collect Landsat 8 science data. The two sensors coincidently collect multispectral digital images of the global land surface including coastal regions, polar ice, islands, and the continental areas. The spacecraft bus stores the OLI and TIRS data on an onboard solid-state recorder and then transmits the data to ground receiving stations.

The ground system provides the capabilities necessary for planning and scheduling the operations of the Landsat 8 observatory and the capabilities necessary to manage the science data following transmission from the spacecraft.

The Landsat 8 spacecraft, built by Orbital Sciences Corporation, has a design life of 5 years, but carries sufficient fuel for 10 years of operations. + 1/48 scale model of Landsat 8 & assembly instructions (PDF, 5 Mb)
Excerpt: LDCM Spacecraft

NASA awarded a contract for the LDCM (Landsat Cool spacecraft to General Dynamics Advanced Information Systems (GDAIS) in April 2008. Orbital Science Corporation (Orbital) subsequently acquired the spacecraft manufacturing division of GDAIS in April 2010. Orbital… assumed responsibility for the design and fabrication of the LDCM spacecraft bus, integration of the two sensors onto the bus, satellite-level testing, on-orbit satellite check-out, and continuing on-orbit engineering support under GSFC contract management (Irons & Dwyer, 2010). The specified design life is five years with an additional requirement to carry sufficient fuel to maintain the LDCM orbit for 10 years; the hope is that the operational lives of the sensors and spacecraft will exceed the design lives and fuel will not limit extended operations. The spacecraft design calls for a three-axis stabilized vehicle built primarily of aluminum honeycomb structure with a hexagonal cross-section. It [was] built in Orbital’s spacecraft manufacturing facility in Gilbert, Arizona.

Excerpted from Remote Sensing of Environment 122, James R. Irons, John L. Dwyer, and Julia A. Barsi , The next Landsat satellite: The Landsat Data Continuity Mission, 11-21, Copyright 2012, doi:10.1016/j.rse.2011.08.026, with permission from Elsevier. Courtesy of the journal Remote Sensing of the Environment.

https://www.nasa.gov/content/landsat-8-instruments

The Operational Land Imager (OLI), built by the Ball Aerospace & Technologies Corporation, measures in the visible, near infrared, and short wave infrared portions of the spectrum. Its images have 15-meter (49 ft.) panchromatic and 30-meter multi-spectral spatial resolutions along a 185 km (115 miles) wide swath, covering wide areas of the Earth’s landscape while providing sufficient resolution to distinguish features like urban centers, farms, forests and other land uses. The entire Earth will fall within view once every 16 days due to Landsat 8’s near-polar orbit.

OLI’s design is an advancement in Landsat sensor technology and uses an approach demonstrated by the Advanced Land Imager sensor flown on NASA’s experimental EO-1 satellite. Instruments on earlier Landsat satellites employed scan mirrors to sweep the instrument fields of view across the surface swath width and transmit light to a few detectors. The OLI instead uses long detector arrays, with over 7,000 detectors per spectral band, aligned across its focal plane to view across the swath. This “push-broom” design results in a more sensitive instrument providing improved land surface information with fewer moving parts. With an improved signal-to-noise ratio compared to past Landsat instruments, OLI is more reliable and provides improved performance.

Read More:

+ Relative Spectral Response:

In-Band Response
Out-of-Band Response

+ OLI Requirements
+ OLI Design
+ Pre-launch OLI Performance

https://landsat.gsfc.nasa.gov/operational-land-imager-oli/

The Thermal Infrared Sensor (TIRS) measures land surface temperature in two thermal bands with a new technology that applies quantum physics to detect heat.

TIRS was added to the satellite mission when it became clear that state water resource managers rely on the highly accurate measurements of Earth’s thermal energy obtained by Landsat 8’s predecessors, Landsat 5 and Landsat 7, to track how land and water are being used. With nearly 80 percent of the fresh water in the Western U.S. being used to irrigate crops, TIRS is an invaluable tool for managing water consumption.

TIRS uses Quantum Well Infrared Photodetectors (QWIPs) to detect long wavelengths of light emitted by the Earth whose intensity depends on surface temperature. These wavelengths, called thermal infrared, are well beyond the range of human vision. QWIPs are a new, lower-cost alternative to conventional infrared technology and were developed at NASA’s Goddard Space Flight Center in Greenbelt, Md.

The QWIPs TIRS uses are sensitive to two thermal infrared wavelength bands, helping it separate the temperature of the Earth’s surface from that of the atmosphere. Their design operates on the complex principles of quantum mechanics. Gallium arsenide semiconductor chips trap electrons in an energy state ‘well’ until the electrons are elevated to a higher state by thermal infrared light of a certain wavelength. The elevated electrons create an electrical signal that can be read out and recorded to create a digital image.

Read More:

+ TIRS Requirements
+ TIRS Design
+ TIRS Relative Spectral Response

https://landsat.gsfc.nasa.gov/thermal-infrared-sensor-tirs/

The Thermal Infrared Sensor (TIRS) measures land surface temperature in two thermal bands with a new technology that applies quantum physics to detect heat.

TIRS was added to the satellite mission when it became clear that state water resource managers rely on the highly accurate measurements of Earth’s thermal energy obtained by Landsat 8’s predecessors, Landsat 5 and Landsat 7, to track how land and water are being used. With nearly 80 percent of the fresh water in the Western U.S. being used to irrigate crops, TIRS is an invaluable tool for managing water consumption.

TIRS uses Quantum Well Infrared Photodetectors (QWIPs) to detect long wavelengths of light emitted by the Earth whose intensity depends on surface temperature. These wavelengths, called thermal infrared, are well beyond the range of human vision. QWIPs are a new, lower-cost alternative to conventional infrared technology and were developed at NASA’s Goddard Space Flight Center in Greenbelt, Md.

The QWIPs TIRS uses are sensitive to two thermal infrared wavelength bands, helping it separate the temperature of the Earth’s surface from that of the atmosphere. Their design operates on the complex principles of quantum mechanics. Gallium arsenide semiconductor chips trap electrons in an energy state ‘well’ until the electrons are elevated to a higher state by thermal infrared light of a certain wavelength. The elevated electrons create an electrical signal that can be read out and recorded to create a digital image.

Read More:

+ TIRS Requirements
+ TIRS Design
+ TIRS Relative Spectral Response

https://www.nasa.gov/content/landsat-8-instruments

RAPPORT DE
Y'BECCA
SOUS LE REGARD DU
CITOYEN TIGNARD YANIS
Revenir en haut Aller en bas
Voir le profil de l'utilisateur http://www.atelier-yannistignard.com
yanis la chouette



Nombre de messages : 7780
Localisation : http://yanis.tignard.free.fr/
Date d'inscription : 09/11/2005

MessageSujet: Re: The Search for Life and Exoplanets, Solar System and Beyond.   Ven 17 Nov à 10:08


China’s Sulfur Dioxide Emissions Drop, India’s Grow Over Last Decade

A new study by researchers at NASA and the University of Maryland indicates that India may be the world’s top sulfur dioxide emitter.

Sulfur dioxide is an air pollutant that causes acid rain, haze and many health-related problems. It is produced predominantly when coal is burned to generate electricity.

https://www.nasa.gov/mission_pages/landsat/news/forest-maps.html
https://www.nasa.gov/mission_pages/landsat/main/index.html
https://www.nasa.gov/topics/solarsystem/index.html

Although China and India remain the world’s largest consumers of coal, the new research found that China’s sulfur dioxide emissions fell by 75 percent since 2007, while India’s emissions increased by 50 percent. The results suggest that India is becoming, if it is not already, the world’s top sulfur dioxide emitter.

“The rapid decrease of sulfur dioxide emissions in China far exceeds expectations and projections,” said first author Can Li, an associate research scientist in the University of Maryland’s Earth System Science Interdisciplinary Center and at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “This suggests that China is implementing sulfur dioxide controls beyond what climate modelers have taken into account.”

The study was published in the journal Scientific Reports on November 9, 2017.

China and India are the world’s top consumers of coal, which typically contains up to 3 percent sulfur. Most of the two countries’ sulfur dioxide emissions come from coal-fired power plants and coal-burning factories. In particular, Beijing suffers from severe haze problems because of the many coal-burning factories and power plants located nearby and upwind.

Starting in the early 2000s, China began implementing policies such as fining polluters, setting emission reduction goals and lowering emissions limits. According to the results of the current study, these efforts are paying off.

“Sulfur dioxide levels in China declined dramatically even though coal usage increased by approximately 50 percent and electricity generation grew by over 100 percent,” explained Li. “This suggests that much of the reduction is coming from controlling emissions.”

Despite China’s 75 percent drop in sulfur dioxide emissions, recent work by other scientists has shown that the country’s air quality remains poor and continues to cause significant health problems. This may be because sulfur dioxide contributes to only approximately 10 to 20 percent of the air particles that cause haze, according to Li.

“If China wants to bring blue skies back to Beijing, the country needs to also control other air pollutants,” Li said.

By contrast, India’s sulfur dioxide emissions increased by 50 percent over the past decade. The country opened its largest coal-fired power plant in 2012 and has yet to implement emission controls like China.

“Right now, India’s increased sulfur dioxide emissions are not causing as many health or haze problems as they do in China because the largest emission sources are not in the most densely populated area of India,” Li said. “However, as demand for electricity grows in India, the impact may worsen.”

To generate an accurate profile of emissions over India and China for the current study, the researchers combined emissions data generated by two different methods.

First, the researchers collected estimated emission amounts from inventories of the number of factories, power plants, automobiles and other contributors to sulfur dioxide emissions. These inventories, while important data sources, are often incomplete, outdated or otherwise inaccurate in developing countries. They also cannot account for changing conditions or unforeseen policies.

The researchers’ second data source was the Ozone Monitoring Instrument (OMI) on NASA’s Aura satellite, which detects a variety of atmospheric pollutants including sulfur dioxide. While OMI can collect up-to-date information and spot emission sources missing from the inventories, it can only detect relatively large emission sources. In addition, clouds or other atmospheric conditions can interfere with its measurements.

To overcome these challenges, Li and his colleagues collaborated with researchers from Environment and Climate Change Canada to develop better algorithms to quantify emissions based on OMI data. In addition, University of Maryland Department of Atmospheric and Oceanic Science Professors Russell Dickerson and Zhanqing Li, co-authors of the paper, used a weather aircraft to measure the concentrations of sulfur dioxide and other air pollutants over one of the most polluted regions in China. These measurements were used to confirm that the upwind coal power plants were efficiently scrubbing SO2 from their exhaust stacks.

By combining the OMI and inventory data, the researchers generated a more accurate estimate than either data source alone. Previously published studies, which relied on inventory data and published policies, projected that China’s sulfur dioxide emissions would not fall to current levels until 2030 at the earliest.

“Those studies did not reflect the true situation on the ground,” said Li, who is also a member of the U.S. OMI Science Team. “Our study highlights the importance of using satellite measurements to study air quality, especially in regions where conditions may change rapidly and unexpectedly.”

Li hopes the current study’s results can be used to improve climate and atmospheric models by providing more accurate input data.

This work was performed in collaboration with Argonne National Laboratory, Environment and Climate Change Canada, Michigan Technological University and NOAA. This study used data from OMI, which is a Dutch/Finnish contribution to the NASA Aura mission and managed by the Royal Meteorological Institute of the Netherlands and the Netherlands Space Agency.

To read the paper, visit: www.nature.com/articles/s41598-017-14639-8

Story written by Irene Ying
University of Maryland
Last Updated: Nov. 13, 2017
Editor: Karl Hille

https://www.nasa.gov/subject/3126/air/
https://www.nasa.gov/topics/earth/index.html

National Aeronautics and Space.
Administration Page Last Updated: Nov. 9, 2017.
Page Editor: Rob Garner.
NASA Official: Brian Dunbar.


https://www.nasa.gov/feature/goddard/2017/chinas-sulfur-dioxide-emissions-drop-indias-grow-over-last-decade

Revenir en haut Aller en bas
Voir le profil de l'utilisateur http://www.atelier-yannistignard.com
yanis la chouette



Nombre de messages : 7780
Localisation : http://yanis.tignard.free.fr/
Date d'inscription : 09/11/2005

MessageSujet: Re: The Search for Life and Exoplanets, Solar System and Beyond.   Ven 17 Nov à 10:12

Nov. 16, 2017
MEDIA ADVISORY M17-136


Nov. 15, 2017
How to See the Atmosphere.



How can you see the atmosphere? The answer is blowing in the wind. Tiny particles, known as aerosols, are carried by winds around the globe. This visualization uses data from NASA satellites combined with our knowledge of physics and meteorology to track three aerosols: dust, smoke, and sea salt.

Sea salt, shown here in blue, is picked up by winds passing over the ocean. As tropical storms and hurricanes form, the salt particles are concentrated into the spiraling shape we all recognize. With their movements, we can follow the formation of Hurricane Irma and see the dust from the Sahara, shown in tan, get washed out of the storm center by the rain. Advances in computing speed allow scientists to include more details of these physical processes in their simulations of how the aerosols interact with the storm systems. The increased resolution of the computer simulation is apparent in fine details like the hurricane bands spiraling counter-clockwise. Computer simulations let us see how different processes fit together and evolve as a system.

By using mathematical models to represent nature we can separate the system into component parts and better understand the underlying physics of each. Today's research improves next year's weather forecasting ability. Hurricane Ophelia was very unusual. It headed northeast, pulling in Saharan dust and smoke from wildfires in Portugal, carrying both to Ireland and the UK. This aerosol interaction was very different from other storms of the season. As computing speed continues to increase, scientists will be able to bring more scientific details into the simulations, giving us a deeper understanding of our home planet.

Watch the video: https://www.youtube.com/watch?v=h1eRp0EGOmE

Image Credit: NASA's Goddard Space Flight Center
Last Updated: Nov. 15, 2017
Editor: Yvette Smith
Tags:  Earth, Image of the Day

NASA Launch of NOAA Weather Satellite Rescheduled for Nov. 18

The launch of the Joint Polar Satellite System-1 (JPSS-1) satellite, the first in a new series of four highly advanced National Oceanic and Atmospheric Administration (NOAA) polar-orbiting satellites, now is scheduled for Saturday, Nov. 18, from Vandenberg Air Force Base, California. Launch coverage will be carried live on NASA Television and the agency’s website.

Liftoff aboard a United Launch Alliance Delta II rocket from Space Launch Complex 2 is targeted for 4:47 a.m. EST (1:47 a.m. PST).

NASA TV launch coverage begins at 4:15 a.m. and will conclude after the deployment of four small satellite missions, called CubeSats, which will accompany JPSS-1 as payload on the Delta II rocket. There is no planned post-launch news conference. A post-launch news release will be issued as soon as the state-of-health of the spacecraft is verified.

JPSS represents significant technological and scientific advancements in observations used for severe weather prediction and environmental monitoring. JPSS is a collaborative effort between NOAA and NASA. The JPSS system will help increase weather forecast accuracy from three to seven days.

Audio only of the news conferences and launch coverage will be carried on the NASA “V” circuits, which may be accessed by dialing 321-867-1220, -1240, -1260 or -7135. On launch day, "mission audio," the launch conductor’s countdown activities without NASA TV launch commentary, will be carried on 321-867-7135.

Additional launch day coverage will be available on NASA.gov. Coverage will include live streaming and blog updates beginning at 4:15 a.m. as countdown milestones occur. You can follow countdown coverage on our launch blog at https://blogs.nasa.gov/jpss.

To learn more about the JPSS-1 mission, visit:

http://www.jpss.noaa.gov

and

https://www.nesdis.noaa.gov/jpss-1

Join the conversation and follow the JPSS-1 mission on social media by using Twitter and Facebook at:

https://twitter.com/NOAASatellites

and

https://www.facebook.com/NOAANESDIS/

-end-

Steve Cole
Headquarters, Washington
202-358-0918
stephen.e.cole@nasa.gov

Tori McLendon
Kennedy Space Center, Florida
321-867-2468
tori.n.mclendon@nasa.gov

John Leslie
NOAA, Washington
301-713-0214
john.leslie@noaa.gov  
Last Updated: Nov. 16, 2017
Editor: Sean Potter
Tags:  Earth, Kennedy Space Center, NOAA

RAPPORT DU
CITOYEN TIGNARD YANIS

https://www.nasa.gov/topics/solarsystem/index.html
https://www.nasa.gov/image-feature/how-to-see-the-atmosphere
https://www.nasa.gov/press-release/nasa-launch-of-noaa-weather-satellite-rescheduled-for-nov-18

"Nous ne nous résignons guère à attribuer du mérite à autrui qu'en raison de celui que nous le croyons disposé à nous attribuer à nous-mêmes."
Citation de Hyacinthe de Charencey ; Pensées et maximes diverses (1888)

"Le côté faible du mérite, même transcendant, c'est qu'il ne suffit pas toujours à nous préserver de la vanité."
Citation de Hyacinthe de Charencey ; Pensées et maximes diverses (1888)

"Le plus grand mérite dans un discours, c'est la clarté."
Citation de Alexandre Dumas, fils ; Le demi-monde, I, 4 (1855)

"La flatterie est une fumée qui obscurcit l'éclat du mérite."
Citation de Antoine Claude Gabriel Jobert ; Le trésor de pensées (1852)

"Le mérite brille moins quand il est trop commun."
Citation de Pierre-Claude-Victor Boiste ; Le dictionnaire universel (1800)

"Le mérite d'autrui incommode les gens vains."
Citation de Antoine Claude Gabriel Jobert ; Le trésor de pensées (1852)

"Le vrai mérite n'a pas de fierté."
Citation de Antoine Claude Gabriel Jobert ; Le trésor de pensées (1852)

"Il faut avoir du mérite pour discerner le mérite dans les autres."
Citation de Antoine Claude Gabriel Jobert ; Le trésor de pensées (1852)

"Le mérite n'est jamais si approuvé que lorsque le bonheur le met en place."
Citation de François Salvat de Montfort ; Vasconiana ou recueil des bons mots (1708)

"Il est plus honorable de confesser ses fautes que de vanter ses mérites."
Citation de Stanislas Leszczynski ; Le philosophe bienfaisant (1764)

"À qui nous trouve beaucoup de mérite, il est presque impossible de ne pas reconnaître un peu de goût."
Citation de John Petit-Senn ; Bluettes et boutades (1846)

"Aujourd'hui, pour le mérite qui fait la violette, le public est enrhumé du cerveau."
Citation de John Petit-Senn ; Bluettes et boutades (1846)

"Souvent le mérite d'un homme disparaît sous le trait du ridicule, comme il ne faut qu'une piqûre d'épingle pour vider une outre de suave liqueur."
Citation de John Petit-Senn ; Bluettes et boutades (1846)

"Le mérite indigent, comme l'aiguille rouillée, perce difficilement."
Citation de John Petit-Senn ; Bluettes et boutades (1846)

"Rabaisser le mérite d'un rival, c'est faire croire que l'on n'a que ce moyen pour l'égaler ; vainqueur, c'est diminuer la valeur de son triomphe ; vaincu, ajouter à la honte de sa défaite."
Citation de John Petit-Senn ; Bluettes et boutades (1846)

"Même en quittant une modeste place, l'homme de mérite laisse un grand vide, car la sphère de son utilité dépasse toujours les limites de son emploi."
Citation de John Petit-Senn ; Bluettes et boutades (1846)

"La vérité sur notre mérite se trouve entre ce qu'on nous en dit par politesse et ce que nous en disons par modestie."
Citation de John Petit-Senn ; Bluettes et boutades (1846)

"Quand on sort de la ligne ordinaire, soit par son mérite, soit par sa position, on a toujours, aux yeux du public, plus ou moins d'importance qu'on ne le croit."
Citation de Constance de Théis ; Pensées diverses (1835)

"Il est facile d'offenser les petits esprits, parce qu'ils se font des mérites d'une foule de choses dont un esprit élevé n'a pas même d'idée."
Citation de Constance de Théis ; Pensées diverses (1835)

"Le mérite est ce que l'on pardonne le moins ; la perversité, ce que l'on tolère le plus : voilà pourquoi il y a tant de tolérance dans le monde."
Citation de Hypolite de Livry ; Pensées et réflexions (1808)

"Le vrai mérite désire d'être honoré, comme il s'honore lui-même."
Citation de Hypolite de Livry ; Pensées et réflexions (1808)

"Il est bon de vous faire une nécessité de plaire par un vrai mérite, au hasard même de déplaire à bien des gens. Ce n'est pas un grand mal de ne pas réussir avec toutes sortes de gens, ou de les perdre après les avoir attachés."
Citation de Vauvenargues ; Réflexions et maximes (1746)

"Le mérite est une monnaie qui n'a plus de cours légal : chacun donne à ses talents le prix qu'il veut ; et souvent les pièces fausses circulent assez longtemps pour qu'elles soient usées lorsqu'on n'en veut plus."
Citation de Édouard Alletz ; Maximes politiques (1840)

"L'homme de mérite est modeste, à proportion qu'il mesure mieux l'espace qui reste encore entre ce qu'il sait et ce qu'il pourrait savoir ; entre ce qu'il fait et ce qu'il pourrait faire. L'homme ordinaire est orgueilleux et vain, à proportion qu'il s'occupe plus de la distance qu'il y a entre l'extrême ignorance et ce qu'il sait ; entre la nullité et ce qu'il est. Ainsi la modestie de l'un vient de ce qu'il regarde toujours au-dessus de lui, comme la fatuité de l'autre, de ce qu'il regardé toujours au-dessous."
Citation de Paul Thiébault ; Recueil de pensées (1805)

"Le mérite isole l'homme plutôt que la médiocrité. Pour le peu qu'elle se recommande par quelque avantage extérieur, la médiocrité se fait partout une petite cour ; comme elle n'offusque pas, chacun s'empresse autour d'elle, on lui sourit, on la prône, on la caresse ; elle a ses partisans, ses amis, ses créatures, et tout ce petit monde fait sa renommée et entretient sa vanité. Mais il n'en est pas ainsi du mérite : comme il efface de son éclat les médiocrités qui l'entourent, il les a toutes pour ennemies ; on le fuit, et en le fuyant on le dénigre : le mérite n'est estimé que par ses pairs."
Citation de Alfred Auguste Pilavoine ; Pensées, mélanges et poésies (1845)

LUCK AND GO, HOUSTON



"On n'est jamais si bien ou si mal recommandé que par son propre mérite."
Citation de Alfred Auguste Pilavoine ; Pensées, mélanges et poésies (1845)

"Ce n'est pas un petit mérite que de savoir découvrir celui des autres."
Citation de Alfred Auguste Pilavoine ; Pensées, mélanges et poésies (1845)

"Aujourd'hui le mérite ne s'estime plus, il se tarife."
Citation de Alfred Auguste Pilavoine ; Pensées, mélanges et poésies (1845)

"Les femmes doivent aux hommes la plupart de leurs défauts, et leur mérite qu'à elles seules."
Citation de Edme de La Taille de Gaubertin ; Pensées et réflexions (1775)

"Il fait bon avoir pour apologistes des hommes d'imagination ; ils nous prêtent volontiers le mérite que nous n'avons pas, et c'est par ce mérite là qu'ils nous font briller davantage."
Citation de Alfred Auguste Pilavoine ; Pensées, mélanges et poésies (1845)

"Combien de fois n'avons-nous pas pris le succès pour le mérite !"
Citation de Alfred Auguste Pilavoine ; Pensées, mélanges et poésies (1845)

"Une grande marque de sagesse, c'est de se faire un mérite de sa position, quand on ne peut s'en faire un bonheur."
Citation de Alfred Auguste Pilavoine ; Pensées, mélanges et poésies (1845)

"Il est aisé d'encenser la vanité, tout encens lui est bon ; il est plus difficile de bien louer le mérite."
Citation de Alfred Auguste Pilavoine ; Pensées, mélanges et poésies (1845)

"On aide volontiers le mérite quand il se tient plus bas que notre orgueil."
Citation de Edme de La Taille de Gaubertin ; Pensées et réflexions (1775)

"Il en est du mérite des hommes comme de l'air, qui plus on monte haut, plus il est rare."
Citation de Edme de La Taille de Gaubertin ; Pensées et réflexions (1775)

"Les louanges qu'on nous donne, prouvent souvent moins notre mérite, que le défaut de mérite de ceux qui nous les donnent."
Citation de Edme de La Taille de Gaubertin ; Pensées et réflexions (1775)

"Ne parle que des gens que tu estimes pour leurs qualités morales ou pour leur mérite ; car ne pensant pas bien des autres, et ton jugement ne pouvant faire loi, il vaut mieux n'en point parler."
Citation de Charles-Jean Baptiste Bonnin ; Doctrine sociale (1820)

"Plus nous parlons de notre mérite, moins on y croit."
Citation de Chauvot de Beauchêne ; Maximes, réflexions et pensées diverses (1819)

"Le mérite n'est pas dans les choses, mais dans le but qu'on se propose en les faisant."
Citation de Hypolite de Livry ; Pensées et réflexions (1808)

"On acquiert du mérite quand on fréquente ceux qui en ont."
Citation de Jean-Baptiste Blanchard ; L'école des mœurs (1772)

"La modestie est toujours inséparable du vrai mérite, et ne se trouve guère qu'avec lui."
Citation de Jean-Baptiste Blanchard ; L'école des mœurs (1772)

"Une grande âme méprise les richesses, parce qu'un riche coffre-fort est un obstacle au vrai mérite."
Citation de Phèdre ; Fables - Ier s. ap. J.-C.

"Souvent nous regrettons moins le mérite d'autrui que d'avoir à le reconnaître."
Citation de Robert Sabatier ; Le livre de la déraison souriante (1991)

"Au sommet du succès, tel se composa une généalogie flatteuse sans se douter que sa vanité niait ses plus humbles mérites."
Citation de Robert Sabatier ; Le livre de la déraison souriante (1991)

"Les mérites étalés se fanent comme les livres trop longuement exposés en vitrine."
Citation de Robert Sabatier ; Le livre de la déraison souriante (1991)

"Le mérite sans dignité est un visage sans physionomie."
Citation de Joseph Sanial-Dubay ; Pensées sur l'homme, le monde et les moeurs (1813)

"Le talent et le mérite donnent successivement la vie et la mort à l'envie."
Citation de Joseph Sanial-Dubay ; Pensées sur l'homme, le monde et les moeurs (1813)

"L'envie est le ver rongeur du mérite et de la gloire."
Citation de Francis Bacon ; Essais (1625)

"Les emplois sont très multipliés, et cependant il en manque pour les hommes de mérite."
Citation de Joseph Sanial-Dubay ; Pensées sur l'homme, le monde et les moeurs (1813)

"Le mérite naît avec les hommes mais ne meurt pas toujours avec eux."
Citation de Christine de Suède ; Maximes et pensées (1682)


Nov. 17, 2017
Taking a Spin on Plasma Space Tornadoes with NASA Observations

Interplanetary space is hardly tranquil. High-energy charged particles from the Sun, as well as from beyond our solar system, constantly whizz by. These can damage satellites and endanger astronaut health — though, luckily for life on Earth, the planet is blanketed by a protective magnetic bubble created by its magnetic field. This bubble, called the magnetosphere, deflects most of the harmful high-energy particles.

Nevertheless, some sneak through — and at the forefront of figuring out just how this happens is NASA’s Magnetospheric Multiscale mission, or MMS. New results show that tornado-like swirls of space plasma create a boundary tumultuous enough to let particles slip into near Earth space.

MMS, launched in 2015, uses four identical spacecraft flying in a pyramid formation to take a three-dimensional look at the magnetic environment around Earth. The mission studies how particles transfer into the magnetosphere by focusing on the causes and effects of magnetic reconnection — an explosive event where magnetic field lines cross, launching electrons and ions from the solar wind into the magnetosphere.

By combining observations from MMS with new 3-D computer simulations, scientists have been able to investigate the small-scale physics of what’s happening at our magnetosphere’s borders for the first time. The results, recently published in a paper in Nature Communications, are key for understanding how the solar wind sometimes enters Earth’s magnetosphere, where it can interfere with satellites and GPS communications.

Inside the magnetosphere, the density of the space plasma — charged particles, like electrons and ions — is much lower than the plasma outside, where the solar wind prevails. The boundary, called the

magnetopause, becomes unstable when the two different density regions move at different rates. Giant swirls, called Kelvin Helmholtz waves, form along the edge like crashing ocean waves. The once-smooth boundary becomes tangled and squeezed, forming plasma tornadoes, which act as portholes for the transportation of charged particles from the solar wind into the magnetosphere.
clouds exhibiting Kelvin-Helmholtz waves
Kelvin-Helmholtz waves, with their classic surfer's wave shape, are found in nature wherever two fluids meet, such as in these clouds.
Credits: Danny Ratcliffe

Kelvin Helmholtz waves are found across the universe wherever two materials of different density move past one another. They can be seen in cloud formations around Earth and have even been observed in other planetary atmospheres in our solar system.

Using large-scale computer simulations of this mixing, performed at the Oak Ridge National Laboratory in Oak Ridge, Tennessee, on the Titan supercomputer, and comparing them to observations MMS took while passing through such a region in space, scientists were able to show that the tornadoes were extremely efficient at transporting charged particles — much more so than previously thought. The comparisons between the simulations and observations allowed the scientists to measure the exact dimensions of the tornadoes. They found these tornadoes to be both large and small — ones reaching 9,300 miles spawned smaller tornadoes 60 to 90 miles wide and over 125 miles long.

MMS recently moved into a new orbit, flying on the far side of Earth, away from the Sun. Here too, it will continue to study magnetic reconnection, but focus instead on how energy and particles interact within Earth’s magnetosphere, in the long trailing magnetotail. Understanding such fundamental processes in Earth’s neighborhood helps improve our situational awareness of the space that surrounds us — crucial information as it becomes ever more filled with satellites and communications systems we depend on.

Related Links

Learn more about the Magnetospheric Multiscale Mission
Learn more about NASA’s research on the Sun-Earth environment

By Mara Johnson-Groh
NASA's Goddard Space Flight Center, Greenbelt, Md.
Last Updated: Nov. 17, 2017
Editor: Rob Garner
Tags: Goddard Space Flight Center, MMS (Magnetospheric Multiscale), Solar System, Sun

RAPPORT DU
CITOYEN TIGNARD YANIS
ALIAS
TAY
La chouette effraie
Revenir en haut Aller en bas
Voir le profil de l'utilisateur http://www.atelier-yannistignard.com
yanis la chouette



Nombre de messages : 7780
Localisation : http://yanis.tignard.free.fr/
Date d'inscription : 09/11/2005

MessageSujet: Re: The Search for Life and Exoplanets, Solar System and Beyond.   Ven 17 Nov à 10:23

How to See the Atmosphere

https://www.nasa.gov/image-feature/how-to-see-the-atmosphere
https://www.nasa.gov/subject/3165/space-weather/

Image Credit: NASA's Goddard Space Flight Center
Last Updated: Nov. 15, 2017
Editor: Yvette Smith
Tags: Earth, Image of the Day

NASA Launch of NOAA Weather Satellite Rescheduled for Nov. 18

The launch of the Joint Polar Satellite System-1 (JPSS-1) satellite, the first in a new series of four highly advanced National Oceanic and Atmospheric Administration (NOAA) polar-orbiting satellites, now is scheduled for Saturday, Nov. 18, from Vandenberg Air Force Base, California. Launch coverage will be carried live on NASA Television and the agency’s website.


Nov. 16, 2017
NASA Detects Solar Flare Pulses at Sun and Earth

When our Sun erupts with giant explosions — such as bursts of radiation called solar flares — we know they can affect space throughout the solar system as well as near Earth. But monitoring their effects requires having observatories in many places with many perspectives, much the way weather sensors all over Earth can help us monitor what’s happening with a terrestrial storm.

By using multiple observatories, two recent studies show how solar flares exhibit pulses or oscillations in the amount of energy being sent out. Such research provides new insights on the origins of these massive solar flares as well as the space weather they produce, which is key information as humans and robotic missions venture out into the solar system, farther and farther from home.

The first study spotted oscillations during a flare — unexpectedly — in measurements of the Sun’s total output of extreme ultraviolet energy, a type of light invisible to human eyes. On Feb. 15, 2011, the Sun emitted an X-class solar flare, the most powerful kind of these intense bursts of radiation. Because scientists had multiple instruments observing the event, they were able to track oscillations in the flare’s radiation, happening simultaneously in several different sets of observations.

“Any type of oscillation on the Sun can tell us a lot about the environment the oscillations are taking place in, or about the physical mechanism responsible for driving changes in emission,” said Ryan Milligan, lead author of this first study and solar physicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and the University of Glasgow in Scotland. In this case, the regular pulses of extreme ultraviolet light indicated disturbances — akin to earthquakes — were rippling through the chromosphere, the base of the Sun’s outer atmosphere, during the flare.

What surprised Milligan about the oscillations was the fact that they were first observed in extreme ultraviolet data from NOAA’s GOES — short for Geostationary Operation Environmental Satellite, which resides in near-Earth space. The mission studies the Sun from Earth’s perspective, collecting X-ray and extreme ultraviolet irradiance data — the total amount of the Sun’s energy that reaches Earth’s atmosphere over time.

This wasn’t a typical data set for Milligan. While GOES helps monitor the effects of solar eruptions in Earth’s space environment — known collectively as space weather — the satellite wasn’t initially designed to detect fine details like these oscillations.

When studying solar flares, Milligan more commonly uses high-resolution data on a specific active region in the Sun’s atmosphere to study the physical processes underlying flares. This is often necessary in order to zoom in on events in a particular area — otherwise they can easily be lost against the backdrop of the Sun’s constant, intense radiation.

“Flares themselves are very localized, so for the oscillations to be detected above the background noise of the Sun’s regular emissions and show up in the irradiance data was very striking,” Milligan said.

There have been previous reports of oscillations in GOES X-ray data coming from the Sun’s upper atmosphere, called the corona, during solar flares. What’s unique in this case is that the pulses were observed in extreme ultraviolet emission at frequencies that show they originated lower, in the chromosphere, providing more information about how a flare’s energy travels throughout through the Sun’s atmosphere.

To be sure the oscillations were real, Milligan and his colleagues checked corresponding data from other Sun-observing instruments on board NASA’s Solar Dynamics Observatory or SDO, for short: one that also collects extreme ultraviolet irradiance data and another that images the corona in different wavelengths of light. They found the exact same pulses in those data sets, confirming they were a phenomenon with its source at the Sun. Their findings are summarized in a paper published in The Astrophysical Journal Letters on Oct. 9, 2017.

These oscillations interest the scientists because they may be the result of a mechanism by which flares emit energy into space — a process we don’t yet fully understand. Additionally, the fact that the oscillations appeared in data sets typically used to monitor larger space patterns suggests they could play a role in driving space weather effects.

In the second study, scientists investigated a connection between solar flares and activity in Earth’s atmosphere. The team discovered that pulses in the electrified layer of the atmosphere — called the ionosphere — mirrored X-ray oscillations during a July 24, 2016, C-class flare. C-class flares are of mid-to-low intensity, and about 100 times weaker than X-flares.

Stretching from roughly 30 to 600 miles above Earth’s surface, the ionosphere is an ever-changing region of the atmosphere that reacts to changes from both Earth below and space above. It swells in response to incoming solar radiation, which ionizes atmospheric gases, and relaxes at night as the charged particles gradually recombine.

In particular, the team of scientists — led by Laura Hayes, a solar physicist who splits her time between NASA Goddard and Trinity College in Dublin, Ireland, and her thesis adviser Peter Gallagher — looked at how the lowest layer of the ionosphere, called the D-region, responded to pulsations in a solar flare.

“This is the region of the ionosphere that affects high-frequency communications and navigation signals,” Hayes said. “Signals travel through the D-region, and changes in the electron density affect whether the signal is absorbed, or degraded.”

The scientists used data from very low frequency, or VLF, radio signals to probe the flare’s effects on the D-region. These were standard communication signals transmitted from Maine and received in Ireland. The denser the ionosphere, the more likely these signals are to run into charged particles along their way from a signal transmitter to its receiver. By monitoring how the VLF signals propagate from one end to the other, scientists can map out changes in electron density.

Pooling together the VLF data and X-ray and extreme ultraviolet observations from GOES and SDO, the team found the D-region’s electron density was pulsing in concert with X-ray pulses on the Sun. They published their results in the Journal of Geophysical Research on Oct. 17, 2017.

“X-rays impinge on the ionosphere and because the amount of X-ray radiation coming in is changing, the amount of ionization in the ionosphere changes too,” said Jack Ireland, a co-author on both studies and Goddard solar physicist. “We’ve seen X-ray oscillations before, but the oscillating ionosphere response hasn’t been detected in the past.”

Hayes and her colleagues used a model to determine just how much the electron density changed during the flare. In response to incoming radiation, they found the density increased as much as 100 times in just 20 minutes during the pulses — an exciting observation for the scientists who didn’t expect oscillating signals in a flare would have such a noticeable effect in the ionosphere. With further study, the team hopes to understand how the ionosphere responds to X-ray oscillations at different timescales, and whether other solar flares induce this response.

“This is an exciting result, showing Earth’s atmosphere is more closely linked to solar X-ray variability than previously thought,” Hayes said. “Now we plan to further explore this dynamic relationship between the Sun and Earth’s atmosphere.”

Both of these studies took advantage of the fact that we are increasingly able to track solar activity and space weather from a number of vantage points. Understanding the space weather that affects us at Earth requires understanding a dynamic system that stretches from the Sun all the way to our upper atmosphere — a system that can only be understood by tapping into a wide range of missions scattered throughout space.

Related:

September 2017’s Intense Solar Activity Viewed from Space
NASA’s ICON Explores the Boundary Between Earth and Space

By Lina Tran
NASA’s Goddard Space Flight Center, Greenbelt, Md.
Last Updated: Nov. 16, 2017
Editor: Rob Garner
Tags: Goddard Space Flight Center, GOES-R, RHESSI (Reuven Ramaty High Energy Solar Spectroscopic Imager), SDO (Solar Dynamics Observatory), Solar System, Space Weather, Sun

https://www.nasa.gov/feature/goddard/2017/nasa-detects-solar-flare-pulses-at-sun-and-earth

La santé est la qualité la plus méritoire du corps.

RAPPORT DU
CITOYEN TIGNARD YANIS
ALIAS
TAY
La chouette effraie
Revenir en haut Aller en bas
Voir le profil de l'utilisateur http://www.atelier-yannistignard.com
yanis la chouette



Nombre de messages : 7780
Localisation : http://yanis.tignard.free.fr/
Date d'inscription : 09/11/2005

MessageSujet: Re: The Search for Life and Exoplanets, Solar System and Beyond.   Ven 17 Nov à 10:32

Nébuleuse obscure
Naissance des étoiles
Description de l'image LH_95.jpg.
Types d'objets Milieu interstellaire
Nuage moléculaire
Globule de Bok
Nébuleuse obscure
Proto-étoile
Étoile variable de type T Tauri
Étoile de la pré-séquence principale
Étoile de Herbig Ae/Be
Objet Herbig-Haro
Concepts théoriques Fonction de masse initiale
Instabilité gravitationnelle
Mécanisme de Kelvin-Helmholtz
Hypothèse de la nébuleuse
Migration planétaire

modifier Consultez la documentation du modèle
Gros plan de la nébuleuse de la Tête de Cheval

En astronomie, les nébuleuses sombres, nébuleuses obscures ou encore nébuleuses d'absorption sont des régions où les poussières du milieu interstellaire semblent se concentrer en grands nuages qui apparaissent en régions pauvres en étoiles.

Les nébuleuses sombres peuvent être vues si elles obscurcissent une partie d'une nébuleuse en émission ou de réflexion, comme la nébuleuse de la Tête de Cheval ou la nébuleuse du Cône dans la constellation de Orion et de la licorne, ou si elles bloquent la lumière des étoiles en arrière-plan, comme le sac de charbon dans la constellation de la Croix du Sud.

La forme de tels nuages est très irrégulière : ils n'ont aucune frontière externe clairement définie et prennent parfois des formes contorsionnées. Les plus grandes nébuleuses sombres sont visibles à l'œil nu, apparaissant comme des zones sombres sur le fond plus lumineux de la Voie lactée.

L'hydrogène de ces nuages sombres et opaques existe sous forme moléculaire (H2). Les plus grandes nébuleuses de ce type, les nuages moléculaires géants, sont plusieurs millions de fois plus massifs que le soleil. Ils contiennent une grande partie de la masse du milieu interstellaire, ont une taille d'environ 150 années-lumière, une densité de matière moyenne de 100 à 300 molécules par centimètre cube et une température interne de seulement de 7 à 15 K. Les nuages moléculaires sont constitués principalement de gaz et de poussières mais peuvent aussi contenir beaucoup d'étoiles. Leurs cœurs sont complètement cachés à la vue et seraient indétectables si leurs molécules constitutives n'émettaient pas dans le domaine des micro-ondes. Ce rayonnement n'est pas absorbé par la poussière et peut donc traverser aisément ces nuages. La matière dans ces nuages est groupée en masses compactes de toutes tailles; les plus petites ayant à peine la taille typique d'une étoile et d'autres s'étendant sur une année-lumière. Ces nuages possèdent un champ magnétique interne qui les empêche de s'effondrer sous l'effet de leur propre gravitation.

Les nuages moléculaires géants jouent un rôle important dans la dynamique des galaxies : quand une étoile passe près d'un nuage géant, l'attraction gravitationnelle considérable de celui-ci perturbera significativement l'orbite de l'étoile. Après de multiples rencontres similaires, une étoile d'un certain âge aura des composantes de vitesse significatives dans toutes les directions, au contraire de l'orbite presque circulaire que les étoiles jeunes héritent du nuage qui les a engendrées. Ceci donne à l'astronome un autre outil pour estimer l'âge des étoiles et contribue à expliquer l'épaisseur du disque galactique.

Les régions internes des nébuleuses sombres sont le siège d'événements importants: la formation des étoiles.


Nov. 16, 2017
Lava or Not, Exoplanet 55 Cancri e Likely to Have Atmosphere

Twice as big as Earth, the super-Earth 55 Cancri e was thought to have lava flows on its surface. The planet is so close to its star, the same side of the planet always faces the star, such that the planet has permanent day and night sides. Based on a 2016 study using data from NASA's Spitzer Space Telescope, scientists speculated that lava would flow freely in lakes on the starlit side and become hardened on the face of perpetual darkness. The lava on the dayside would reflect radiation from the star, contributing to the overall observed temperature of the planet.

Now, a deeper analysis of the same Spitzer data finds this planet likely has an atmosphere whose ingredients could be similar to those of Earth's atmosphere, but thicker. Lava lakes directly exposed to space without an atmosphere would create local hot spots of high temperatures, so they are not the best explanation for the Spitzer observations, scientists said.

"If there is lava on this planet, it would need to cover the entire surface," said Renyu Hu, astronomer at NASA's Jet Propulsion Laboratory, Pasadena, California, and co-author of a study published in The Astronomical Journal. "But the lava would be hidden from our view by the thick atmosphere."

Using an improved model of how energy would flow throughout the planet and radiate back into space, researchers find that the night side of the planet is not as cool as previously thought. The "cold" side is still quite toasty by Earthly standards, with an average of 2,400 to 2,600 degrees Fahrenheit (1,300 to 1,400 Celsius), and the hot side averages 4,200 degrees Fahrenheit (2,300 Celsius). The difference between the hot and cold sides would need to be more extreme if there were no atmosphere.

"Scientists have been debating whether this planet has an atmosphere like Earth and Venus, or just a rocky core and no atmosphere, like Mercury. The case for an atmosphere is now stronger than ever," Hu said.

Researchers say the atmosphere of this mysterious planet could contain nitrogen, water and even oxygen -- molecules found in our atmosphere, too -- but with much higher temperatures throughout. The density of the planet is also similar to Earth, suggesting that it, too, is rocky. The intense heat from the host star would be far too great to support life, however, and could not maintain liquid water.

Hu developed a method of studying exoplanet atmospheres and surfaces, and had previously only applied it to sizzling, giant gaseous planets called hot Jupiters. Isabel Angelo, first author of the study and a senior at the University of California, Berkeley, worked on the study as part of her internship at JPL and adapted Hu's model to 55 Cancri e.

In a seminar, she heard about 55 Cancri e as a potentially carbon-rich planet, so high in temperature and pressure that its interior could contain a large amount of diamond.

"It's an exoplanet whose nature is pretty contested, which I thought was exciting," Angelo said.

Spitzer observed 55 Cancri e between June 15 and July 15, 2013, using a camera specially designed for viewing infrared light, which is invisible to human eyes. Infrared light is an indicator of heat energy. By comparing changes in brightness Spitzer observed to the energy flow models, researchers realized an atmosphere with volatile materials could best explain the temperatures.

There are many open questions about 55 Cancri e, especially: Why has the atmosphere not been stripped away from the planet, given the perilous radiation environment of the star?

"Understanding this planet will help us address larger questions about the evolution of rocky planets," Hu said.

NASA's Jet Propulsion Laboratory, Pasadena, California, manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at Caltech in Pasadena. Spacecraft operations are based at Lockheed Martin Space Systems Company, Littleton, Colorado. Data are archived at the Infrared Science Archive housed at IPAC at Caltech. Caltech manages JPL for NASA. For more information about Spitzer, visit:

http://spitzer.caltech.edu

https://www.nasa.gov/spitzer

Elizabeth Landau
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6425
elizabeth.landau@jpl.nasa.gov

2017-296
Last Updated: Nov. 16, 2017
Editor: Tony Greicius

https://www.nasa.gov/feature/jpl/lava-or-not-exoplanet-55-cancri-e-likely-to-have-atmosphere

"Les passions sont dans la vie des espèces de gîtes, où les voyageurs, comme dans les autres gîtes, entrent avec joie et d'où ils sortent en querellant."
Citation de Joseph Michel Antoine Servan ; Extrait d'un portefeuille (1807)

"L'histoire de la race humaine a été une suite de guerres, de massacres, de pillages, de divisions interminables, d'oppositions mutuelles à un état de paix et de bonheur, une longue période dans laquelle chacun a été en lutte avec tous et tous avec chacun, principe de conduite admirablement calculé pour enfanter le moins de prospérité et le plus de misère possible !"
Citation de Robert Owen ; Pensées diverses (1852)

"Il y a des femmes qui sont nées pour tout brouiller."
Citation de Pedro Calderón de la Barca ; Bonheur et malheur du nom (1639)

"Terribles sont les querelles et les luttes entre frères, quand la discorde les divise."
Citation de Euripide ; Iphigénie à Aulis - Ve s. av. J.-C.


"Les dépits amoureux, les brouilles, les querelles, resserrent les liens des amants et des belles."
Citation de Publilius Syrus ; Sentences - Ier s. av. J.-C.

"Il ne suffit pas d'épouser la querelle de nos amis, il faut en faire sa maîtresse."
Citation de Jean Louis Auguste Commerson ; Petite encyclopédie bouffonne (1860)

"Gens fatigués sont querelleurs."
Citation de Sénèque ; De la colère - Vers 47 ap. J.-C.

"Tout être faible est naturellement querelleur."
Citation de Sénèque ; De la colère - Vers 47 ap. J.-C.

"L'incertitude des événements est toujours plus difficile à soutenir que l'événement même."
Citation de Jean-Baptiste Massillon ; Maximes et pensées (1742)

"La honte suit de près les courages timides."
Citation de Jean Racine ; Alexandre le Grand (1665)

"Le bonheur et le malheur finissent où l'indifférence commence."
Citation de Paul Thiébault ; Recueil de pensées (1805)

"Il n'est rien dont ne puissent triompher la persévérance, l'attention et les soins soutenus."
Citation de Sénèque ; Lettres à Lucilius - Vers 64 ap. J.-C.

RAPPORT DU
CITOYEN TIGNARD YANIS
ALIAS
TAY
La chouette effraie
Revenir en haut Aller en bas
Voir le profil de l'utilisateur http://www.atelier-yannistignard.com
yanis la chouette



Nombre de messages : 7780
Localisation : http://yanis.tignard.free.fr/
Date d'inscription : 09/11/2005

MessageSujet: Re: The Search for Life and Exoplanets, Solar System and Beyond.   Ven 17 Nov à 10:40

Dark and Diffuse Nebulae

April 28, 2014 by Brian Ventrudo

On a dark night, as you gaze along the arc of the Milky Way, you will see small patches of diffuse light and other patches where there appear to be few stars. These are diffuse nebulae and dark nebulae, respectively. These patches are made of gas and dust, and the are places where new stars form.

Dark Nebulae

Many of these patches are so-called dark nebulae where cool gas and interstellar dust block the view of the background stars. These nebulae are laced across the spiral arms of the Milky Way in irregular patches and rivulets without definite shape or boundaries.

Dark nebulae are part of cool, giant molecular clouds where dust and gas from old stars and gas from the earliest days of the universe slowly pull themselves together by gravity. The icy dust grains are less than 1/1,000 of a millimeter across, but they have an interesting chemistry, consisting of frozen nitrogen, carbon monoxide, ammonia, formaldehyde, and more complex organic molecules (even ethyl alcohol).

Because dark nebulae are the birthplace of stars and planets, astronomers find them intensely interesting. Computer modeling shows that although the nebulae are tenuous, with only a few particles per cubic centimeter, passing stars push and pull on the particles, causing them to coalesce into denser patches that begin to fall in on themselves and heat up. Hundreds of tiny globules in a dark nebula may eventually become hot enough to start the process of nuclear fusion, where hydrogen in the center of the globule begins to burn into helium, releasing huge amounts of energy. When this happens, dense globules of gas and dust turn into clusters of new stars which light up the remaining dust and gas into what astronomers call diffuse nebulae.
Diffuse Nebulae

After a dark cloud of gas and dust collapses into dense globules that ignite into stars, the leftover material is set aglow by the intense blue and ultraviolet light from newly formed stars. The glowing hydrogen gas surrounding the stars is called an “emission nebula”.

These nebulae usually glow a reddish-pink color. That’s because the new stars excite the atoms of hydrogen gas that remain in the cloud, and the atoms relax again by emitting red light at 656 nm, a wavelength set by the structure of the hydrogen atom. Emission nebulae also have traces of ionized oxygen which also emit light at a characteristic wavelength near 500 nm (blue-green). In a way, emission nebulae are much like the neon lights you see on buildings and billboards. The lights use electricity to make gases glow, while an emission nebula gets its energy from the light of new stars embedded within.

These nebulae also contain a fair bit of dust that reflects the blue light of the new stars. The reflective dust is called a “reflection nebula”; in many cases, the two nebulae occur in the same area of star formation (see the image of the Trifid Nebula, below).

Both emission nebulae and reflection nebulae are sometimes called diffuse nebulae.
The Trifid Nebula in the constellation Sagittarius. Red light comes from hydrogen gas atoms excited by the light from stars within the nebula; blue light from these stars is re-flected off fine dust particles back into our line of sight

The Trifid Nebula in the constellation Sagittarius. Red light comes from hydrogen gas atoms excited by the light from stars within the nebula; blue light from these stars is re-flected off fine dust particles back into our line of sight

The Trifid Nebula in the constellation Sagittarius. Red light comes from hydrogen gas atoms excited by the light from stars within the nebula; blue light from these stars is reflected off fine dust particles back into our line of sight.

Even a random search with a small telescope along the plane of the Milky Way reveals many diffuse nebulae which look like hazy patches of silver-white light. The sword of the constellation Orion contains one of the brightest and most famous such nebulae. It’s often just called the Orion Nebula. A telescope gives you an astoundingly beautiful view of the Orion Nebula; no amount of observation is enough to reveal all its detail. You can see many more such nebulae such as the Swan, Lagoon, Trifid, and eta Carina nebulae with a small telescope or pair of binoculars. Just remember, you won’t see color when you observe such nebulae visually; there isn’t enough light to stimulate the color-sensing cells in your eye. But in dark sky, these objects are still quite striking.

Diffuse nebulae don’t last long, at least on astronomical time scales. After a few million years, the hot young stars burn off the remaining gas and dust, leaving a small loose cluster of gravitationally-associated stars.

Filed Under: Guide To Star Gazing

Un globule de Bok est un amas sombre de poussières et de gaz du milieu interstellaire au sein duquel peut commencer la naissance des étoiles. Ils sont courants dans les régions HII et ont typiquement une masse d'environ 10 à 50 masses solaires contenue dans un volume d'environ une année-lumière1. Ils contiennent de l'hydrogène moléculaire (H2), des oxydes de carbone, de l'hélium et environ 1 % (en masse) de poussières de silicates. Les globules de Bok conduisent le plus souvent à la formation de systèmes d'étoiles doubles ou multiples2.

Observation

Les globules de Bok furent observés pour la première fois par l'astronome Bart Bok dans les années 1940. Dans un article publié en 1947, Bok et E.F. Reilly firent l'hypothèse que ces nuages étaient « similaires à des cocons d'insectes » en cours d'effondrement gravitationnel pour former des proto-étoiles à partir desquelles les étoiles et les amas d'étoiles naissent3. Cette hypothèse était difficile à vérifier à cause des difficultés d'observation pour comprendre ce qui se passait à l'intérieur d'un nuage dense et sombre qui absorbait toute la lumière visible émise à l'intérieur. Une analyse d'observations faites dans le proche infrarouge publiée en 1990 a confirmé que les étoiles naissaient bien à l'intérieur des globules de Bok4.

Des observations ultérieures ont montré que certains globules de Bok contenaient des objets chauds1, d'autres des objets Herbig-Haro5, et que certains expulsaient du gaz moléculaire6. Des études des raies d'émission en ondes millimétriques ont aussi montré l'existence de chute de matière sur une proto-étoile en accrétion7.

Les globules de Bok sont encore un sujet de recherche très actif. Connus pour être parmi les objets les plus froids de l'univers naturel (jusqu'à 3 kelvins), leur structure et leur densité demeurent assez mystérieuses. Les méthodes utilisées jusqu'à présent reposent sur la densité de colonne déduite de mesures d'extinction en infrarouge proche et même sur le comptage d'étoiles pour tenter de sonder ces objets plus profondément.
Notes et références

↑ a et b (en) Clemens D.P., Yun, J.L., Heyer M.H. (1991). Bok globules and small molecular clouds – Deep IRAS photometry and (C-12)O spectroscopy, Astrophysical Journal Supplement, v.75, p. 877
↑ (en) Launhardt R., Sargent A.I., Henning T., et al. (2002). Binary and multiple star formation in Bok globules, Proceedings of IAU Symposium No. 200 on The Formation of Binary Stars. Eds Reipurth & Zinnecker, p. 103
↑ (en) Bok, B. J., Reilly, E. F. (1947). Small Dark Nebulae, Astrophysical Journal, v.105, p. 255
↑ (en) Yun J.L., Clemens D.P. (1990). Star formation in small globules – Bart Bok was correct, Astrophysical Journal, v.365, p.L73
↑ (en) Reipurth, B., Heathcote, S., & Vrba, F. (1992), Star formation in Bok globules and low-mass clouds. IV - Herbig-Haro objects in B335, Astronomy & Astrophysics, v.256, p. 225
↑ (en) Yun, J. L., & Clemens, D. P. (1992). Discovery of outflows from young stellar objects in BOK globules, Astrophysical Journal, v.385, p.L21
↑ (en) Zhou, S., Evans, N. J., II, Kömpe, C., & Walmsley, C. M. (1993). Evidence for protostellar collapse in B335, Astrophysical Journal, v.404, p. 232

Voir également
Articles connexes

IC 2944
Nuage moléculaire géant

Types d'objets Milieu interstellaire
Nuage moléculaire
Globule de Bok
Nébuleuse obscure
Proto-étoile
Étoile variable de type T Tauri
Étoile de la pré-séquence principale
Étoile de Herbig Ae/Be
Objet Herbig-Haro
Concepts théoriques Fonction de masse initiale
Instabilité gravitationnelle
Mécanisme de Kelvin-Helmholtz
Hypothèse de la nébuleuse
Migration planétaire


Nov. 17, 2017
The Search for Life Beyond Earth: A Special Live NASA Event
We’ve discovered thousands of worlds orbiting around other stars, called exoplanets, including many that are similar in size to Earth. But how do we know if some of these worlds might support life?

NASA has formed a community of scientists to apply what we’ve learned from our home planet to better understand the habitability of worlds beyond our solar system. On Friday, Nov. 17 from 1-2 PM ET, they’ll provide an update and overview of their efforts during a livestream event, “Next Steps in the Search for Habitable Worlds,” from the Habitable Worlds workshop in Laramie, Wyoming.

The one-hour interactive discussion will cross traditional disciplinary boundaries, encompassing much of the broad research topics supported by NASA’s Science Mission Directorate. Five researchers will address topics that include:
• What makes a planet habitable? What does “habitability” mean when it comes to exoplanets?
• How does a star impact a planet’s habitability?
• Why do we focus on Earth-like planets? Could life appear on much stranger worlds than ours and, if so, could we recognize it?
• How can we confirm that a planet around another star is habitable? And how might we find life on such a world?
• How does our observations and understanding of Earth inform our search for life on planets around other stars?

The live event can be accessed at:

www.nasa.gov/nasatv

The public may submit questions before and during the live event on Twitter using #AskNASA.
Last Updated: Nov. 17, 2017
Editor: Tricia Talbert
Tags: Astrobiology, Exoplanets, Solar System

https://www.nasa.gov/image-feature/how-to-see-the-atmosphere
https://www.nasa.gov/content/the-search-for-life
https://fr.wikipedia.org/wiki/Globule_de_Bok
https://www.nasa.gov/subject/3165/space-weather/

RAPPORT DU
CITOYEN TIGNARD YANIS
ALIAS
TAY
La chouette effraie

National Aeronautics and Space Administration.
Page Last Updated: Aug. 4, 2017.
Page Editor: Brian Dunbar NASA Official: Brian Dunbar.

"L'incertitude des événements est toujours plus difficile à soutenir que l'événement même."
Citation de Jean-Baptiste Massillon ; Maximes et pensées (1742)

"La honte suit de près les courages timides."
Citation de Jean Racine ; Alexandre le Grand (1665)

"Le bonheur et le malheur finissent où l'indifférence commence."
Citation de Paul Thiébault ; Recueil de pensées (1805)

"Il n'est rien dont ne puissent triompher la persévérance, l'attention et les soins soutenus."
Citation de Sénèque ; Lettres à Lucilius - Vers 64 ap. J.-C.

RAPPORT DU
CITOYEN TIGNARD YANIS
ALIAS
TAY
La chouette effraie
Revenir en haut Aller en bas
Voir le profil de l'utilisateur http://www.atelier-yannistignard.com
yanis la chouette



Nombre de messages : 7780
Localisation : http://yanis.tignard.free.fr/
Date d'inscription : 09/11/2005

MessageSujet: Re: The Search for Life and Exoplanets, Solar System and Beyond.   Ven 17 Nov à 10:46

Processus de Paix des secouristes de la république de l'Olivier.

Je crois qu'à l'avenir, plus personne ne pourra recréer des bulles d'exclusions...
Pour cela, je ne peux me permettre de mettre à l'écart tout individu(e) et "État".

Je ne suis qu'une femme ou un homme humble qui en vous adressant ces ces vers,
espère qu'il puisse vous conduire vers l'expérience, le travail et la communauté...
La solitude augmente ou diminue le nervosité... Cela s'appelle le malheur...

Alors par décision, on recherche à se tranquilliser et remettre la balance sur le zéro;
alors par construction, on décèle la notion d'une fragile tolérance:
Celle d'insulter !

Par Yahvé, cela est une horreur et une erreur...

La République de l'Olivier dit :
"Oui à la gréve, Non à l'Esclavage..."
la constitution rajoute :
"Oui à la Bibliothèque et Non à la Faim."
et le peuple doit rajouter :
"Oui à l'écoute et Non aux viols physiques et moraux."

Alors le Novice du Secourisme prends en charge sa nouvelle fonction autre qu'un service
militaire mais basé aussi sur la protection du Bien et du Corps.

"Je suis Y'becca"

Ecrit de
TAY
La chouette effraie.

-----------------------------------------

Y'becca est soumis à toujours suivre un dossier médical, on ne peut se reposer sur des radios anciennes et toutes opérations auquel Lise Verdier ne peut être bâclé... Certains medecins oublient d'osculter la gorge quand un patien à une fiévre... Il est des gestes de précautions auquel la médecine n'a pas la droit de s'occulter... Y'becca doit répondre à ces faits là et son secouriste ne doit jamais dire jamais sur le fait que l'expérience ne donne jamais d'acquis et il est une chose auquel je voue une grande discipline et rigueur: Celle d'entendre la Prudence lorsque le temps le permet... quel que soit l'opération, on agit avec prudence du temps, de l'aspect et des allergies possibles auquel le patient ou la patiente peut être soumis en fonction de son age et de sa corpulence...

"La grâce est à la beauté ce que la souplesse est à la rose. Sans grâce, la beauté n'est qu'une fleur artificielle, qu'un colibri sans vie."
Citation de Jean-Napoléon Vernier ; Fables, pensées et poésies (1865). L'association pour Lise et pour vous, s'inspire de cette citation de Jean-Napoléon Vernier qui est si réelle sur l'aspect du courage d'être dans des situation auquel l'aspect humain se doit de se reconsidérer dans l'aspect de l'adversité dans l'être. Cette citation cherche à nous monter des aspects qui nous semblent enfoie par l'adversité et la douleur mais qui ne demande qu'à renaitre afin de permettre à la rose de devenir Rosier...


Aide pour le retour à domicile d’une personne lourdement handicapée.

L’Association Pour Lise et pour Vous, a but non lucratif, met à la disposition des personnes en situation de grand handicap et leurs familles, son expertise dans la prise en charge du retour au domicile.

Plus largement, l’association veut favoriser et permettre le développement des soins de qualité et le maintien à son domicile de tout enfant, adolescent ou jeune adulte, atteint d’une maladie grave ou d’un handicap lourd.

Nous sommes à votre écoute pour parler et construire ensemble de votre projet de vie, nous sommes à vos côtés pour le concrétiser.


Pour Lise Et Pour Vous
le Bourg Chevreau, 53600 SAINTE GEMMES LE ROBERT
Association humanitaire, d'entraide, sociale



"La grâce est à la beauté ce que la souplesse est à la rose. Sans grâce, la beauté n'est qu'une fleur artificielle, qu'un colibri sans vie."
Citation de Jean-Napoléon Vernier ; Fables, pensées et poésies (1865)

"La beauté sans grâce est un printemps sans verdure."
Citation de Mirabeau ; Lettres à Sophie Ruffei (1777-1780)

"La beauté sans grâce est un hameçon sans appâts."
Citation de Ninon de Lenclos ; Confessions (1700)

"On admire d'un coup d'œil la beauté, elle ne laisse plus rien à deviner ; la grâce se fait aimer peu à peu par des détails variés, imprévus, qui vous plaisent d'autant plus qu'ils vous surprennent, et ses petits défauts d'ensemble sont quelquefois des charmes qui nous attachent."
Citation de Louis-Philippe de Ségur ; L'ennui (1816)

"La grâce, ce charme suprême de la beauté, ne se développe que dans le repos du naturel."
Citation de Madame de Staël ; L'influence des passions (1796)

"La beauté ne déplaît jamais, mais sans la grâce, elle est dépourvue de ce charme secret qui invite à la regarder."
Citation de Voltaire ; Dictionnaire philosophique (1764)

"Les grâces préférables à la beauté, ornent la femme de tous ce qu'elles ont de séduisant."
Citation de Marie-Geneviève-Charlotte Darlus ; Traité des passions (1764)

"Il y a un art caché dans la simplicité qui donne une grâce à l'esprit et à la beauté."
Citation de Alexander Pope ; Maximes et réflexions morales (1739)

"Aucune grâce extérieure n'est complète si la beauté intérieure ne la vivifie."
Citation de Victor Hugo ; Post-scriptum de ma vie (1901)

"Brillante de beauté, de grâces, de jeunesse, pour vous plaire, on accourt, on s'empresse."
Citation de Charles-Guillaume Étienne ; L'Intrigante, I, 9, le 6 mars 1813.

"Sans le fard de l'amour, par qui tout s'apprécie, les grâces sont sans force, et la beauté sans vie."
Citation de Antoine Bret ; La double extravagance, VII, le 27 juillet 1750.

"La beauté est la clef des coeurs, la grâce le passe-partout."
Citation de Paul Masson ; Les pensées d'un Yoghi (1896)

"La beauté réside dans la forme ; la grâce dans les mouvements, le charme dans l'expression."
Citation de Lucien Arréat ; Réflexions et maximes (1911)

"La grâce, plus belle encore que la beauté."
Citation de Jean de La Fontaine ; Adonis (1658)

Compte rendu de
TAY
La chouette effraie

Tikkun Ha-Klali
https://www.youtube.com/watch?v=MPZhFy2c3Mc
TAY
Revenir en haut Aller en bas
Voir le profil de l'utilisateur http://www.atelier-yannistignard.com
Contenu sponsorisé




MessageSujet: Re: The Search for Life and Exoplanets, Solar System and Beyond.   

Revenir en haut Aller en bas
 
The Search for Life and Exoplanets, Solar System and Beyond.
Voir le sujet précédent Voir le sujet suivant Revenir en haut 
Page 1 sur 1
 Sujets similaires
-
» Pour un Conteur en recherche d'aide... (DK System)
» — bring me to life
» Life in UCLA
» 06. My life would suck without you (part II)
» 01. life is beautiful ? …Maybe ! Pv. Finn

Permission de ce forum:Vous ne pouvez pas répondre aux sujets dans ce forum
Le clans des mouettes :: Le clans des mouettes-
Sauter vers: