Saturday, December 5, 2015

Tonight's Sky for December 5: The Earliest Sunsets, Moon at Apogee

While the shortest day of the year, the Winter Solstice, is about two weeks away, the earliest sunsets of the year will occur this week for us here on Earth, regardless of where you live, despite the fact that sunset times vary depending on latitude.
Right now, the Sun is setting at its earliest time and will continue to set at the same time for the next few days before gradually creeping later into the evening.
So, with the Sun down so early (and resulting in the longest nights of the year), why not head out and view the stars? After all, the December sky has a lot to offer. After all, at what point of the year can you see a year's worth of stars in a given night? Don't believe me? Head out just after dark tonight and look up for the Summer Triangle. Then, just before sunrise, go out again and look for a bright blue star in the Northeast just above the horizon. That's Vega, the same Summer Triangle Star you saw the previous night.

Additionally, the Moon is about as small as it will ever get thanks to the fact that the Moon is at apogee, a point in its orbit that is farthest from Earth.

What many people may not realize is the fact that the Moon (and all other celestial bodies) do not orbit their parent bodies in circles, but ellipses, which are slightly elongated circles. Result: any given day of an orbital period, any orbiting body will be at a slightly different distance from its parent body. As for the Moon, this variance in orbit amounts to about 20,000 miles.

As for tonight, the Moon will be about as far from Earth as it is going to get. When it comes to practical implications, the difference will be hard to notice with the naked eye to all but an experienced observer but, in a telescope, the difference will be obvious

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