Photograph by NASA/Goddard/Lunar Reconnaissance Orbiter
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A full moon will shine bright early Christmas morning. This rare event won’t happen again until 2034. That’s a long time to wait, so make sure to look up to the skies on Christmas Day.

Photograph by NASA/Goddard/Lunar Reconnaissance Orbiter

This Week’s Night Sky: Winter Solstice and a Christmas Moon

Celebrate the shortest (or longest) day of the year, and check out the holiday season’s best celestial events.

Winter solstice.  The sun reaches its lowest point in the sky at exactly 11:48 p.m. ET on Monday, making it the shortest day of the year north of the equator.

On the flip side, December 21 is the longest day in the Southern Hemisphere. At this time of year, Earth’s northern axis is slightly tilted away from the sun, so the Northern Hemisphere receives less sunlight and experiences winter, while the Southern Hemisphere enjoys summer.

The exact date and time of the winter solstice always fall around December 21, but shift slightly from year to year because of the difference between a calendar year of 365 days and the solar year of 365.26 days: the exact time it takes Earth to make one trip around the sun.

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At dawn on Tuesday, Mars will have a close encounter with Spica, the brightest star in the Virgo constellation. 

Mars and Spica.  Early risers who are up by dawn on Tuesday, December 22, can catch the Red Planet snuggling up with the blue-white diamond-like Spica, the brightest star in the constellation Virgo, the maiden.

It’s amazing to think that despite the two celestial orbs appearing so close in our skies, Mars sits nearly 15 light-minutes from Earth, while Spica is an astounding 250 light-years distant. That means the light by which we see this bright star left on its journey the same year that the British parliament passed the Stamp Act, the first direct tax imposed on American colonies.

Ursid Meteor Shower.  In your local pre-dawn hours of Tuesday, December 22, a minor meteor shower will peak in northern skies.

As with all meteor showers, the Ursids are named after the constellation that they appear to radiate out from in the sky—in this case, Ursa Minor. Meteors appear to shoot from a region of sky just above the bowl of the Little Dipper.

While the Ursids produce on average only about 10 to 15 shooting stars per hour, at rare times there are bursts of 30 or more per hour. The comet that produces the meteors is 8P/Tuttle; Earth plows through the debris shed from this icy visitor between December 17 and 23. Unfortunately, this year meteor watchers will have to contend with a nearly full moon, so expect to see the show nearly washed out with perhaps fewer than half a dozen meteors visible per hour.

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On Wednesday night, The Moon will appear to glide by Adlebaran – the red eye of Taurus, the bull.

Moon Hides Aldebaran.  As darkness fall on Wednesday, December 23, the nearly full moon appears to next to the bright orange star Aldebaran.

For lucky skywatchers in northern Asia and Europe, the 66 light-year-distant lead star in the constellation Taurus will actually be eclipsed or occulted by the moon. But this cosmic disappearing act will be visible virtually around the world thanks to the webcast by the Virtual Telescope Project beginning at 12:45 p.m. ET (17:45 UT).  

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The King Cobra open star cluster is bright enough to be seen with binoculars and is as wide as the full moon in the sky. It'll be visible late Sunday evening in the lower eastern sky.

Christmas Full Moon.  Waking up early on Christmas morning? Then check out the pretty full moon that officially reaches full phase at 6:11 a.m. ET.

This will be the first full moon timed with Christmas since 1977, and won’t happen again until 2034.  But if you aren’t an early bird then you can catch the silver orb rising around sunset in the east the night before and at its highest point in the southern sky around midnight. You can find it rising in the east around sunset and peaking high in the south close to midnight. So it looks like Santa will have a bright lunar glow this year to help him get around.

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On Sunday evening, the Moon will guide binocular and telescope users to two pretty star clusters in the constellation Cancer, the crab.

Cluster Sandwich.  By Sunday night the waning gibbous Moon will be visible in the lower eastern sky late in the evening wedged in between two beautiful winter star clusters.

Using binoculars or better yet, a telescope, scan about 5 degrees (equal to the width of your three middle fingers held at arm’s length) to the upper left of Luna to find the 600 light year distant Beehive open star cluster (M44) while to its lower right at 3 degrees away is another stunning King Cobra open cluster (M67) that sits at 2,600 light years away.  Both clusters will be competing with the glare of the moon tonight, but by the next night they will shine much brighter as the moon sinks closer to the horizon.  

Clear skies!

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