Astronomy

Understanding the Phases of the Moon



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On a clear night, a person could look into the sky and see the moon. It is the Earth’s closest heavenly neighbor and has become a central part of our folklore, scientific research and literature. And, long before men walked on the moon, the moon’s phases have caused people to wonder about why and how they happen.

Celestial pair

The moon and the Earth co-exist in a special celestial relationship.  Every 365 days the Earth revolves around sun and every 27.3 days, the moon circles the Earth.  As the Earth and moon move along their paths sunlight reflects from each; however, depending on when and what angle the moon is in its monthly journey and people on Earth will see the light reflected differently and these changes are what we see as the phases of the moon.

What are the moon phases

The moon travels through a very specific cycle and the phases are a way of knowing where the moon is in its cycle around the earth.  If you think of the moon like a ball travel around a circular track the phases are easier to visualize.

 The different moon phases are typically called New Moon, Waxing Crescent Moon, Half Moon (First Quarter), Waxing Gibbous Moon, Full Moon, Waning Gibbous, Waning Crescent. A phase is considered to be a waning when lit is getting smaller or decreasing. And, a phase is considered waxing if the lit surface grows or increases.

The celestial dance - why moon phases occur

Phases of the moon are affected by the angle in which people see the reflected sunlight off the moon’s surface from the Earth’s perspective.  At the start of the moon cycle, known as the New Moon, the moon is between the Earth and the sun or in front of the Earth.  The side of the moon reflecting light cannot be seen.

As the moon moves around, the angles at which sunlight hits the lunar surface appear to change from our perspective.  By the time the waxing or waning Crescent phases occur, the moon is at a 45 degree angle.  If the movement were seen overhead, the moon would look slightly in front of the Earth.

When the Moon is in the First Half Moon phase, the sun, Earth and moon form a ninety degree or right angle with the Earth as the vertex of the angle. In simpler terms, the moon seems to be on the side of the Earth. When the Moon is in its Second Half Moon Phase, the right angle is a 270 degree angle. And, these phases appear to be the mirror images of the earlier phase.

The Gibbous Phase is the mirror opposite of the Crescent Phase.  During the Gibbous Phase, the moon is slightly behind the Earth at a either a 135 degree during the Waxing Gibbous Phase or 315 degree angle during the Waning Gibbous Phase. More of the moon’s face is lit as these are the phases that come before and after a full moon.

By the time the Full Moon phase occurs, the moon is in the 14th day of its 27-plus day cycle.  The Earth is between the moon and the sun and the reflecting surface will appear to be a perfect circle.

Phases v. Eclipses

Moon phases are not like lunar eclipses.  In the case of a lunar eclipse, the Earth’s shadow blocks the light on the moon’s surface.  Eclipses are not as common as phase changes.

With various Blue, Wolf, Hunter’s, Super and Rose Moons, our Mmon remains an interesting celestial neighbor.  Its phases continue to help us mark time as well as enjoy the beauty of the night sky.

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More about this author: Ramona Taylor

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ARTICLE SOURCES AND CITATIONS
  • InfoBoxCallToAction ActionArrowhttp://www.nytimes.com/learning/general/onthisday/big/0720.html
  • InfoBoxCallToAction ActionArrowhttp://www.moonconnection.com/moon_phases.phtml
  • InfoBoxCallToAction ActionArrowhttp://www.moonconnection.com/moon_cycle.phtml
  • InfoBoxCallToAction ActionArrowhttp://www.nasa.gov/mission_pages/LRO/news/eclipse-video.html
  • InfoBoxCallToAction ActionArrowhttp://www.universetoday.com/102763/what-is-a-super-moon/