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Eclipsing Independence

What's Up? by Adam England

On July 4 we celebrate the Declaration of Independence of the United States from the monarchy of Britain. Traditional ceremonies include community parades, neighborhood barbecues, fireworks, and here in Prescott, we rodeo. After all those festivities, beginning at 8:07 MST, a penumbral lunar eclipse will grace our skies.

A lunar eclipse occurs when the Earth passes directly between the moon and sun. As this puts the two on directly opposite sides of the planet, it also creates 100% illumination of the moon’s visible surface, or the lunar phase we call a full moon. 


Just after 8pm the moon will begin to slide into the outermost edge of the Earth’s shadow, called the penumbra. At 9:29 MST the moon will be at its dimmest and furthest into the shadow as we can see from Northern Arizona. The darkest eclipses pass through the center of the Earth’s shadow cone, called the umbra. This eclipse will not reach the umbra, and only about a third of the moon’s surface will cross the penumbral edge. The astute lunar observer will notice a darkening of the moon’s surface, should the weather permit us to see it at all. The first week of July traditionally signals the influx of the monsoon season and daily thunderstorms, with a 34% chance of cloudy skies over the last 20 years. If you still have a little energy remaining after a long Arizona summer day, and the heavens permit us to see it, look to the moon as it gives a nod to the terrestrial fireworks celebrating American independence.


To learn more about the sky, telescopes, or socialize with other amateur astronomers, visit us at prescottastronomyclub.org or Facebook @PrescottAstronomyClub to find the next star party, Star Talk, or event. Adam England is a local insurance broker who moonlights as an amateur astronomer, writer, and interplanetary conquest consultant. Follow his rants and exploits on Twitter @AZSalesman or at Facebook.com/AdamEfromAZ.

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