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Super Autumn Moon Show Spectacular

September 24, 2010

Rheanna Sand

Science in Seconds Blog by Rheanna Sand

 

Did you know that every full moon has a name? The June full moon is often called the Rose Moon or Strawberry Moon, depending on what's blooming in the area. The October full moon is named the Hunter's Moon. The one in December, paradoxically, is called the Cold Moon.

 

September's is of course the Harvest Moon, which happened yesterday in a particularly unusual combination of celestial circumstances.

 

First, in an event that happens only once during the moon's 19-year metonic cycle, the Harvest Moon and the autumnal equinox coincided. At least, the difference between them was small, only five and a half hours apart.

 

The equinox is one of two points in Earth's orbit around the Sun where we have no apparent tilt in our axis, and thus day and night are approximately equal length. If you live in the northern hemisphere, it is also the official end of summer (sorry, undergrads still clinging to shorts).

 



The second coincidence is that right now Jupiter and Uranus are very visibly lined up with the moon. Jupiter can be spotted without a telescope as the bright star just below it. Uranus is smaller and just to the upper left of Jupiter.


So why does a Harvest Moon only happen once a year? According to the Royal Astronomical Society of Canada, there are a mulitude of reasons. For one, the moon and earth's orbits are both ellipses, and tilted with respect to each other, meaning the distance and relative speed between them is always changing.

 

Plus, the apparent rise time of the moon depends on where you are on the globe. Add to that the fact that the moon's orbit is not exactly one month, and you have enough complexity to create once-in-a-year, and once-in-every-19-years phenomena like that rare sight witnessed last night.

 

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