The Night Sky This Month: December 2021

Winter Solstice

This year, the Winter Solstice occurs at 5:50 UTC on the 21st of December. At this time, the Sun will be directly over the Tropic of Capricorn, which marks the first day of winter in the Northern Hemisphere, and the first day of summer in the Southern Hemisphere.

A partial solar eclipse will occur on the 4th of December, but this event will not be visible for northern observers. The path of visibility will be restricted to Antarctica and large parts of Southern Africa.

The Moon Phases in 2021

New Moon First Quarter Full Moon Third Quarter
December 3rd December 10th December 18th December 26th

The Planets in December 2021

Planetary viewing is still poor, but for those observers that are up for the challenge of looking for planets low on the horizon or close to the Sun, here are some details of what to expect:

Mercury becomes visible shortly after sunset on the last few days of December, but will remain within a few degrees of the southwestern horizon. Nonetheless, during the few minutes that the planet will be visible, it will be seen shining at about magnitude -0.73 just below Venus.

Venus starts the month shining at magnitude -4.87 and with an angular diameter of about 39 seconds of arc, but will remain below around 8 degrees above the south-southwestern horizon. Since the ecliptic is now at a very shallow angle relative to the horizon, Venus will not rise above about 10 degrees during the month.

Mars is now visible as a pre-dawn object, shining at magnitude 1.64 at the start of the month. It will be visible from about 06:41 GMT at the start of the month, and from about 07:00 GMT during the last half of the month. This does not leave much time for observing the planet before the Sun rises, so be sure not to use binoculars to observe Mars after the Sun has risen.

Jupiter rises just after darkness falls at the start of December, and it will shine at magnitude -2.29 when it crosses the meridian at 17:15 GMT. Note though, that the ‘King of the Planets’ has now risen somewhat from the southern part of the ecliptic, and it will reach an elevation of about 24 degrees at its culmination. Sadly, though, by month’s end, its brightness will have reduced somewhat to magnitude -2.13, and its angular diameter will have shrunk from 38.3 seconds of arc to 35.36 seconds of arc.

Saturn rises a few minutes before Jupiter, and although it will shine relatively brightly at magnitude +0.7 when darkness falls, the planet will remain below about 17 degrees above the southern horizon. As a result, it may be difficult to obtain clear views of the planet through the atmospheric murk and haze.

-Uranus is easy to spot with binoculars throughout the month, and from a very dark site, it might even be possible to spot the planet without optical aid. If, however, you have access to a medium-sized telescope, you might even be able to discern its turquoise color. Look for the planet in Aries close to the border with Cetus where it will shine at magnitude 5.7 for most of December.

Meteor Showers in December 2021

December sees two meteor showers, these being:

The Geminids Meteor Shower, which is expected to peak on the night of the 13th / 14th of December this year, is considered by most observers to be the most productive shower in the entire sky. In fact, at its peak, it typically produces around 120 large, multi-colored meteors that are fragments left behind by the asteroid 3200 Phaethon. Sadly, though, the waxing gibbous Moon will extinguish most of the fainter meteors, but this shower is so productive that a few dozen bright meteors will still be visible per hour during the peak hours. Note while the radiant of the shower is in the constellation Gemini, Geminids can appear from almost any point in the sky.

– The Ursids Meteor Shower will peak on the night of 21st / 22nd December, but it rarely produces more than about 10 or so meteors per hour at its peak- even in its most productive years. Moreover, this year, the Moon will be nearly full during the peak, meaning that you can expect to see no more than about three or four bright meteors per hour, which is about equal to the normal background meteor activity at this time of the year.

Deep Sky Objects to Look for in December 2021

Some of the prominent constellations at this time of the year include Perseus, Taurus, Orion, Gemini, Cygnus, Cassiopeia, and Andromeda, which contains the Andromeda Galaxy, our nearest and biggest neighbor in the Local Group of Galaxies. Collectively, these constellations contain a large number of objects that are easy targets for modest amateur observing equipment, so provided seeing conditions allow, you might want to see if you can spot the few objects we have listed here-

The Hyades and Pleiades

Both are located in the constellation Taurus, with the Hyades cluster seen to the lower left, and the Pleiades to the upper right. The Pleiades cluster contains more than 3,000 stars that are both similar in composition and share a similar motion across the sky, which suggests a common origin for all the stars in the cluster.

Double Cluster

Both clusters, designated NGC 869 and NGC 884, are located in the constellation Perseus, and are surrounded by a single, but extensive outer halo of stars. Both clusters and the halo weigh in at an estimated combined mass of about 20,000 solar masses, and are approaching Earth at speeds of 39 km/s and 38 km/s, respectively.

The two clusters are visible as a patch of light without optical aid, which likely explains their very long observational history. For instance, the ancient Greek astronomer first listed the pair of clusters in about 130 BCE, while the ancient Arabian astronomer Abd al-Rahman al-Sufi listed them in his Book of Fixed Stars in about the year 964 AD.

Orion Nebula

The Orion Nebula is a large star-forming region in Orion. Most optical images will show it as a shade of reddish-brown, which is about the closest possible approximation of the nebula’s true color. However, to most observers, the Orion Nebula has a greenish-tint, since human vision is more sensitive to the green light emitted by ionized oxygen in the nebula than to the reddish light emitted by hydrogen atoms.

Related Articles