The smallest and largest of the Sun’s major planets will stage a relatively rare encounter this month as they pass each other in the dawn twilight. Jupiter should be easy to see, but Mercury could take some work. The great Winter Circle climbs higher each night, and is in good view by 8 p.m. by month’s end. It consists of seven bright stars encircling orange Betelgeuse, the shoulder of Orion.
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In the Sky This Month
December 18: Zodiac
As twilight fades away, the zodiac arcs high across the southern sky. It is a trail of constellations with one thing in common: The Sun’s path across the sky traverses their borders, so the Sun passes through each of those constellations during the year.
December 19: Jupiter and Mercury
Jupiter and Mercury, the largest and smallest of the solar system’s major planets, are getting together in the dawn sky. For the next few days, they will be separated by less than the width of your finger held at arm’s length. Jupiter is the brighter of the two.
December 20: Moon and Aldebaran
The eye of the bull — the star Aldebaran — stares into the Moon tonight. The brightest star of Taurus is to the lower left of the Moon at nightfall. The Moon will move closer to Aldebaran during the night, to less than the width of a finger held at arm’s length.
December 21: Solstice
Today is the winter solstice. It is the shortest day of the year in the northern hemisphere. The Sun rises late, sets early, and scoots low across the sky during the day. The Moon is full, so it is in view longer than any other full Moon of the year.
December 22: Long-Night Moon
The Moon is full today at 11:49 a.m. CST. As the full Moon closest to the winter solstice, which was yesterday, it is the Long-Night Moon. It will be visible longer than any other full Moon of the year.
December 23: Wise Stars
Orion, the hunter, stands well up in the east and southeast by about 8 p.m. Its most prominent feature is a row of three stars known as Orion’s Belt. Early Christians associated those stars with the Three Magi, the wise men who brought gifts to baby Jesus.
December 24: Messier 34
The star cluster Messier 34 sits on the border between the constellations Perseus and Andromeda. It is high overhead during the evening, between two bright stars. Under a clear, dark sky, M34 is just visible to the unaided eye as a fuzzy patch of light.