Northern winter solstice on December 21, 2021 | SkyNews
Northern winter solstice on December 21, 2021 (Chris Vaughan, Starry Night Education)

This Week’s Sky: December 20 to 26, 2021

This week, we’ll mark the December solstice, the longest night of the year in the Northern Hemisphere. Also look for Ursid meteors and a meetup between Mars and Antares.

Tuesday, December 21 – Northern winter solstice (at 15:59 GMT)

Northern winter solstice on December 21, 2021 | SkyNews
Northern winter solstice on December 21, 2021 (Chris Vaughan, Starry Night Education)

Winter in the Northern Hemisphere will officially commence on Tuesday, December 21 at 15:59 GMT (or 10:59 a.m. EST and 7:59 a.m. PST). At that time, the Sun will reach the solstice — its southernmost declination for the year — resulting in the lowest noonday Sun, the shortest amount of daylight of the year for the Northern Hemisphere, and the longest amount for the Southern Hemisphere. After the December solstice, the daylight hours will begin to increase for the Northern Hemisphere.

Wednesday, December 22 – Ursid Meteor Shower peak (pre-dawn)

Ursid Meteor Shower peak on December 22, 2021 | SkyNews
Ursid Meteor Shower peak on December 22, 2021 (Chris Vaughan, Starry Night Education)

The annual Ursids meteor shower, produced by debris dropped by periodic comet 8P/Tuttle, runs from December 13 to 24. The short shower will peak during the early hours of Wednesday, December 22, when seeing 5-10 meteors per hour is possible under dark skies. The best time to watch will be the hours before dawn. Unfortunately, a waning gibbous Moon will shine in the post-midnight sky, spoiling the show for this year. True Ursids will appear to radiate from a position in the sky above the Little Dipper (Ursa Minor) near Polaris, but the meteors can appear anywhere in the sky. 

Saturday, December 25 – A Christmas star (late evening)

A Christmas star on December 25, 2021 | SkyNews
A Christmas star on December 25, 2021 (Chris Vaughan, Starry Night Education)

Sirius — the brightest star in Canis Major and the brightest star in the sky (after the Sun) — rises in the southeast by 7 p.m. local time. It’s hard to miss. The star will climb to its highest point, about a third of the way up the southern sky shortly after midnight. If you are walking through your darkened house in the middle of the night, Sirius will probably catch your eye out a window because it never climbs very high. Sirius is a hot, blue-white, A-class star located only 8.6 light-years from the Sun. Its extreme brightness and its low position in the sky combine to produce spectacular flashes of colour as it twinkles. A very large telescope may allow you to see Sirius B, a faint white dwarf companion located 10 arc-seconds east from Sirius.

Sunday, December 26 – Mars passes its rival (pre-dawn)

Mars passes its rival on December 26, 2021 | SkyNews
Mars passes its rival on December 26, 2021 (Chris Vaughan, Starry Night Education)

Low in the southeastern pre-dawn sky on the mornings surrounding Sunday, December 26, the motion of the red planet Mars (red path with date:time) will carry it past its “rival,” the bright star Antares in Scorpius. At its closest approach on December 27, Mars will shine several finger widths to the upper right (or 4.5 degrees to the celestial north) of the star, but they’ll be binoculars-close (green circle) from December 23 to 31, with Antares shifting higher each morning. Antares will appear slightly brighter than the planet, but it will exhibit a similar reddish — hence their rivalry! The optimal viewing time at mid-northern latitudes will be around 6:30 a.m. local time. Observers at southerly latitudes will see the duo shining higher, in a darker sky.

Monday, December 27 – Third quarter Moon (at 02:23 GMT)

Third quarter Moon on December 26/27, 2021 | SkyNews
Third quarter Moon on December 26/27, 2021 (Chris Vaughan, Starry Night Education)

When it reaches its last quarter phase at 02:23 GMT on Monday, December 27 (or 9:23 p.m. EST on Sunday), the Moon will rise at about midnight, and then remain visible in the southern sky all morning. At last quarter, the Moon is illuminated on its western side, towards the pre-dawn Sun. Last quarter Moons are positioned ahead of the Earth in our trip around the Sun. About 3.5 hours later, Earth will occupy that same location in space. The week of moonless evening skies that follow last quarter will be ideal for observing deep-sky targets.

Chris Vaughan is a science writer, geophysicist, astronomer, planetary scientist and an “outreach RASCal.” He writes Astronomy Skylights, and you can follow him on Twitter at @astrogeoguy. He can also bring his Digital Starlab portable inflatable planetarium to your school or other daytime or evening event. Contact him through AstroGeo.ca to tour the Universe together.

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