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Lunar Phases


 

Moon Phases (click to see large version)    The moon goes through phases because of the way it orbits the Earth and Sun.  When the moon is between the Earth and the Sun, we see a new moon -- there is no moon in the night sky.  In the next few days after a new moon, we start to see a tiny sliver of moon a few hours after sunrise in the morning.  These slivers of moon increase in size each day, and during this phase we have a waxing crescent moon .  The moon will rise about an hour later each day.  Around 7 days after a new moon, the moon will appear halfway illuminated and will rise when the Sun is highest in the sky for that day -- a first quarter moon .  The portion of the moon which is illuminated by the Sun continues to increase.  Next we have a waxing gibbous moon .

Image: U.S. Naval Observatory - Astronomical Applications Department.

 

    Halfway through the lunar cycle, at 14 days, the side of the moon we see is fully illuminated by the sun.  The Earth is between the Sun and the moon -- a full moon .  After a full moon, the portion illuminated decreases.  We see a waning gibbous moon .  At 21 days after the new moon, the moon is only halfway lit by the Sun -- a third quarter moon .  At this point the moon is again visible during the day (remember the moon rises about an hour later each day), it rises before the sun.  When the moon is again just a sliver, it is called a waning crescent moon .

 

Astronomical Society of the Pacific

 

 

For more information on moon phases, visit the Astronomical Society of the Pacific's web page at http://www.astrosociety.org/education/publications/tnl/12/12.html or the US Naval Observatory's web page at http://aa.usno.navy.mil/faq/docs/moon_phases.html.

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Website last updated March 16,  2006.  Hosted by Anthony Watts, KMXI Radio.  Webmasters Tiara Norris and Brendan Diamond.