Dec 20

Sky Report: December 20 – December 26

Spend a few minutes to understand why the night side of the earth faces different constellations at different times of the year. In one month the earth moves 1/12 of the way around the sun, so in that same month the stars move 30° (1/12 of 360) eastward (counterclockwise) around the sun and at night the night side of the earth faces the next constellation to the east. Consequently the constellations shift 30° westward. The stars are fixed in space and the earth returns to face the same constellations after one year, but in that year Jupiter moves roughly 30° eastward (counterclockwise) and Saturn 12° eastward against the background of stars. Jupiter moves to the next constellation to the east each year while Saturn takes 2½ years to move to the next constellation, and Jupiter quickly leaves Saturn behind.
Credit: NASA/JPL-Caltech.

Venus continues its rapid descent out of the evening sky, setting 3 minutes earlier each night as it moves between the earth and sun. This was explained in detail in earlier Sky Reports which are archived at Say good-by to the Evening Star.

Jupiter and Saturn are low in the west, to the left of Venus, and they too set earlier each night, but for a different reason. We’re not seeing their motion around the sun but the consequence of the earth’s motion. As we orbit the sun the night side of the earth faces a slightly different direction in space each day. In a month we’ve moved 1/12 of the way around the sun and the part of the universe we face has shifted 1/12 to the left. In that time Jupiter, Saturn, and the stars beyond move 1/12 of the way around the sky to the right, and set 1/12 of a day, or 2 hours, earlier. We’ll lose Saturn next month and Jupiter in February – and then the evening sky will be devoid of bright planets and will look quite bare.

Uranus and Neptune are in the evening sky too, and if you have binoculars you can see Uranus and any small telescope will show Neptune, but the trick is to know where to look. In olden days one would get their coordinates from an almanac and plot their positions on a star chart; nowadays one uses an app like SkySafari (my favorite) which does everything except point your telescope, and if you have a computerized telescope it will even do that. Neptune is as far to the left of Jupiter as Saturn is to Jupiter’s right, in Aquarius, and Uranus is much farther to the left, in Aries.

December 21 marks the winter solstice, the shortest day of the year (in the northern hemisphere!) and the day when the sun rises and sets as far south as it will during the year and its noontime elevation is at its lowest. For stargazers, it’s the longest night! The precise time of the solstice is 8:58 a.m. MST and that’s the first day of winter. Seasons happen because the earth is tilted on its axis; Google “winter solstice” for a complete explanation.

The Ursid Meteor Shower also peaks on the night of the 21st. This is a minor shower of interest only to specialists; don’t bother.

Thanks to a grant from the Utah Governor’s Office of Economic Development and the Kane County Office of Tourism, Stellar Vista Observatory offers portable telescopes and tripod mounted binocular kits on loan for free to all residents of Kane County. Nothing beats a quality binocular or astronomical telescope to enhance enjoyment of the night sky! Visit or Kanab City Library for full details.

The Sky Report is presented as a public service by the Stellar Vista Observatory, a nonprofit organization based in Kanab, Utah, which provides opportunities for people to observe, appreciate, and comprehend our starry night sky. Additional information is at Send questions and comments to

About the Author:

John Mosley was Program Supervisor of the Griffith Observatory in Los Angeles for 27 years and is the author of “Stargazing for Beginners” and “Stargazing with Binoculars and Telescopes”. He and his wife live in St. George where he continues to stargaze from his retirement home while serving on the advisory committee for Stellar Vista Observatory.

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