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Earth's Atmosphere

The atmosphere is a mixture of nitrogen (78%), oxygen (21%), and other gases (1%) that surrounds Earth. High above the planet, the atmosphere becomes thinner until it gradually reaches space. It is divided into five layers. Most of the weather and clouds are found in the first layer.

The atmosphere is an important part of what makes Earth livable. It blocks some of the Sun's dangerous rays from reaching Earth. It traps heat, making Earth a comfortable temperature. And the oxygen within our atmosphere is essential for life.

Over the past century, greenhouse gases and other air pollutants released into the atmosphere have been causing big changes like global warming, ozone holes, and acid rain.

<a href="/earth/Atmosphere/NLC.html">Noctilucent</a>
  clouds are the highest clouds in the sky, but they are not associated with
  weather like the <a
  href="/earth/Atmosphere/clouds/cloud_types.html">other
  clouds</a> we regularly see in the sky.  Noctilucent clouds form very high in
  the <a href="/earth/Atmosphere/overview.html">atmosphere</a>,
  in the <a
  href="/earth/Atmosphere/mesosphere.html">mesosphere</a>. 
  They are best seen from Earth at sunset. This image was taken on June 15,
  2007, in Budapest, Hungary.  Normally seen from locations near the <a
  href="/earth/polar/polar.html">poles</a> of
  the Earth, in recent years they have also been seen at much lower-latitude
  locations.<p><small><em> Image Courtesy of NASA/Veres Viktor</em></small></p><a
  href="/earth/Atmosphere/clouds/lenticular.html">Lenticular
  clouds</a> form on the downwind side of mountains. <a
  href="/earth/Atmosphere/wind.html">Wind</a>
  blows most types of clouds across the sky, but lenticular clouds seem to stay
  in one place. Air moves up and over a mountain, and at the point where the
  air goes past the mountaintop the lenticular cloud forms, and then the air <a
  href="/earth/Water/evaporation.html">evaporates</a>
  on the side farther away from the mountains.  This close up of lenticular
  clouds was taken at sunset on November 20, 2006 in Boulder, Colorado.<p><small><em>       Courtesy of Roberta Johnson</em></small></p>Anti-crepuscular rays are beams of sunlight that appear to converge on a point opposite the sun. They are similar to crepuscular rays, but are seen opposite the sun in the sky. Anti-crepuscular rays are most frequently visible near sunrise or sunset. This photo of anti-crepuscular rays was taken at sunset in Boulder, Colorado. Crepuscular rays are usually much brighter than anti-crepuscular rays.<p><small><em> Image Courtesy of Carlye Calvin</em></small></p>On November 7, 2013, Typhoon Haiyan (Yolanda in the Philippines) made landfall, with imated wind speeds of ~315 km/hr - the strongest <a href="/earth/Atmosphere/hurricane/intensity.html">tropical cyclone</a> to make landfall in recorded history.  As Haiyan moved across the Philippines before reaching Vietnam and China, its <a href="/earth/Atmosphere/wind.html">winds</a> and <a href="/earth/Atmosphere/hurricane/surge.html">storm surge</a> left devastation in its wake, leading to massive loss of life, destruction of homes, and hundreds of thousands of displaced inhabitants. <a href="http://www.cnn.com/2013/11/09/world/iyw-how-to-help-typhoon-haiyan/index.html">How to Help</a><p><small><em>Image courtesy of COMS-1, SSEC, University of Wisconsin-Madison</em></small></p>On May 20, 2013, a massive EF5 <a href="http://www.windows2universe.org/earth/Atmosphere/tornado.html">tornado</a> hit Moore, Oklahoma, devastating communities and lives.  The tornado, on the ground for 40 minutes, took a path through a subdivision of homes, destroying block after block of homes, and hitting two elementary schools just as school was ending as well as a hospital. Hundreds of people were injured, and 24 were killed.<p><small><em>Image courtesy of Ks0stm, Creative Commons Attribution-Share Alike 3.0 Unported license</em></small></p>Greenland’s <a href="http://www.windows2universe.org/earth/polar/cryosphere_glacier1.html">ice sheet</a> saw a record <a href="http://www.windows2universe.org/headline_universe/olpa/greenland_10dec07.html">melt</a> in July 2012.  Scientists studying this event have found that this melting event was triggered by an influx of unusually warm air and amplified by the presence of a blanket of thin low-level <a href="http://www.windows2universe.org/earth/Atmosphere/cloud.html">clouds</a> which pushed temperatures up above freezing.  For more information see the <a href="http://www.news.wisc.edu/21638">press release</a> from the University of Wisconsin Madison.<p><small><em>Image courtesy of University of Wisconsin-Madison</em></small></p>

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA