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>How did life evolve on <a href="/earth/earth.html">Earth</a> during the <a href="/earth/past/Archean.html">Archean</a>, when the <a href="/sun/sun.html">Sun</a> was about 25% weaker than today?  The Earth should have been <a href="/earth/polar/cryosphere_glacier1.html">glaciated</a>, if <a href="/earth/climate/earth_greenhouse.html">greenhouse</a> gas concentration was the same as today.  <a href="">Researchers</a> studying the <a href="/physical_science/physics/atom_particle/isotope.html">isotopic</a> signatures of Earth's early atmosphere in <a href="/earth/geology/rocks_intro.html">rocks</a> from Northern Australia have ruled out high levels of <a href="/physical_science/chemistry/nitrogen_molecular.html">nitrogen</a> as a possible way to increase warming from <a href="/earth/Atmosphere/overview.html">atmospheric</a> <a href="/physical_science/chemistry/carbon_dioxide.html">carbon dioxide</a>.<p><small><em>Image courtesy of Manchester University</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">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">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>According to <a href="">NASA scientists</a>, the Voyager 1 spacecraft entered interstellar space in August 2012, becoming the first spacecraft to leave the <a href="/our_solar_system/solar_system.html">solar system</a>. The space probe is about 19 billion km from the <a href="/sun/sun.html">Sun</a>.  <a href="/space_missions/voyager.html">Voyager 1 and 2</a> were launched in 1977 on a <a href="/space_missions/voyager.html">mission</a> that flew them both by <a href="/jupiter/jupiter.html">Jupiter</a> and <a href="/saturn/saturn.html">Saturn</a>, with Voyager 2 continuing to <a href="/uranus/uranus.html">Uranus</a> and <a href="/neptune/neptune.html">Neptune</a>. Voyager 2 is the longest continuously operated spacecraft. It is about 15 billion km away from the <a href="/sun/sun.html">Sun</a>.<p><small><em>Image courtesy of NASA</em></small></p>The spinning vortex of <a href="">Saturn</a>'s north polar storm resembles a giant deep red rose surrounded by green foliage in this false-color <a href="">image</a> from NASA's <a href="">Cassini spacecraft</a>. The eye is 2,000 kilometers across with cloud speeds as fast as 150 meters per second.
It is not known how long this newly discovered north-polar <a href="">hurricane</a> has been active.
The view was acquired at a distance of approximately 419,000 kilometers from Saturn.<p><small><em>NASA/JPL-Caltech/SSI</em></small></p>