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Learn about planets outside our solar system through Exoplanets and Alien Solar Systems by Tahir Yaqoob, Ph.D., a book in our online store book collection.


Earth, our home planet, is a beautiful blue and white ball when seen from space. The third planet from the Sun, it is the largest of the inner planets. Earth is the only planet known to support life and to have liquid water at the surface. Earth has a substantial atmosphere and magnetic field, both of which are critical for sustaining life on Earth. Earth is the innermost planet in the solar system with a natural satellite – our Moon. Explore our beautiful home planet – unique in our solar system - through the links in this section.

This iconic image of Earth rising above the surface of the <a
  was taken on December 24, 1968 by astronauts on the <a
  href="/space_missions/apollo8.html&edu=high">Apollo 8
  mission</a>. Apollo 8 was the first <a
  mission</a> to the Moon, and entered into lunar orbit on Christmas Eve. That
  evening, the astronauts held a live broadcast from lunar orbit, in which they showed pictures of the Earth and moon as seen from their
  spacecraft.<p><small><em> Image courtesy of   NASA</em></small></p>How did life evolve on <a href="/earth/earth.html&edu=high">Earth</a> during the <a href="/earth/past/Archean.html&edu=high">Archean</a>, when the <a href="/sun/sun.html&edu=high">Sun</a> was about 25% weaker than today?  The Earth should have been <a href="/earth/polar/cryosphere_glacier1.html&edu=high">glaciated</a>, if <a href="/earth/climate/earth_greenhouse.html&edu=high">greenhouse</a> gas concentration was the same as today.  <a href="">Researchers</a> studying the <a href="/physical_science/physics/atom_particle/isotope.html&edu=high">isotopic</a> signatures of Earth's early atmosphere in <a href="/earth/geology/rocks_intro.html&edu=high">rocks</a> from Northern Australia have ruled out high levels of <a href="/physical_science/chemistry/nitrogen_molecular.html&edu=high">nitrogen</a> as a possible way to increase warming from <a href="/earth/Atmosphere/overview.html&edu=high">atmospheric</a> <a href="/physical_science/chemistry/carbon_dioxide.html&edu=high">carbon dioxide</a>.<p><small><em>Image courtesy of Manchester University</em></small></p>A view of the Earth as seen by the <a href="/space_missions/apollo17.html&edu=high">Apollo
17</a> crew
while traveling to the
<a href="/earth/moons_and_rings.html&edu=high">Moon</a> on
December 7, 1972.  Africa, Madagascar, and the Arabian Peninsula are
visible, and you can barely make out the
<a href="/earth/polar/antarctica.html&edu=high">Antarctic</a>,
shrouded in the heavy
<a href="/earth/Atmosphere/cloud.html&edu=high">cloud</a> cover
in the southern hemisphere.
Arching cloud patterns show the presence of <a href="/earth/Atmosphere/front.html&edu=high">weather
fronts</a>.<p><small><em>Image courtesy of NASA/Apollo 17.</em></small></p>Scientists are concerned that melting Arctic sea ice will increase the amount of fresh water in the <a href="/earth/polar/arctic_currents.html&edu=high">Beaufort Gyre</a>, which could spill out into the Atlantic and cause major climate shifts in North America and Western Europe. Watch the <a href="/earth/changing_planet/freshwater_arctic.html&edu=high">Changing Planet: Fresh Water in the Arctic video</a>.<p><small><em> Courtesy of Jack Cook, WHOI (<a href="">Woods Hole Oceanographic Institute</a>)</em></small></p>Coral animals build reefs in warm, tropical seawater. However, <a href="/earth/changing_planet/ocean_temperatures_intro.html&edu=high">seawater can be too warm</a> for their liking.  If waters get too warm, coral animals lose the algae that live within their little bodies, a process called coral bleaching. Without the algae, corals have less nutrition. Unless cooler temperatures return, allowing algae to
 return, the coral dies.<p><small><em>Credit: UNC</em></small></p>A sinuous glowing band of <a
  href="/earth/Magnetosphere/aurora.html&edu=high">aurora</a> (the Aurora Australis
  or Southern Lights) loops around the <a
  href="/earth/polar/polar_south.html&edu=high">southern polar</a>
region in the
  distance as viewed by astronauts onboard the space shuttle on <a
  href="/earth/Magnetosphere/aurora/aurora_colors.html&edu=high">Aurora are produced</a>
  when <a
  href="/physical_science/physics/atom_particle/particle_radiation.html&edu=high">energetic particles</a>
 entering the Earth's
  atmosphere from space interact with <a
  href="/physical_science/physics/atom_particle/atom.html&edu=high">atoms</a> and <a
  href="/earth/geology/molecule.html&edu=high">molecules</a> in the atmosphere and
  release energy, emitted as light.<p><small><em>Courtesy of NASA, Astronaut Overmeyer and Dr. Hallinan</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