Skywatcher's Guide: December 2021 and January 2022

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Stars and Constellations

In December, the summer constellations are still visible for the first few hours of the night towards the west.  The Summer Triangle is still fairly high, with Vega heading to the west-northwest, Deneb closest to the zenith, and Altair in the west-southwest.  The center of the Milky Way is now below the horizon, but there is still a good portion of our galaxy we can see streaking high across the sky. The fall sky is now very prominent, getting high in the eastern sky.  The "W" of Cassiopeia is very high in the north-northeast. In the absence of the Big Dipper (part of our spring sky) Cassiopeia can be used to locate the north star: The top (open side) of the "W" faces to the north, so in that direction look for a star about the same brightness as the main stars in Casssiopeia, and that will most likely be Polaris.  Next, the Great Square of Pegasus is nearly in the middle of the sky.  Andromeda is nearby in the northeast, with Perseus just below.  There is also a fairly bright star called Fomalhaut in the south, though its constellation Piscis Austrinus is not easy to distinguish.  Finally, the winter sky is beginning to come up along the eastern horizon.  Taurus the bull is now up in the east with the bright star Aldebaran and the Pleiades (aka the seven sisters or Subaru) star cluster.  Auriga the charioteer is also up in the northeast, with the bright star Capella.

In January, the summer constellations are now very low in the west.  Deneb is the highest point of the Summer Triangle in the northwest, with Vega below near the horizon, and Altair more towards the west.  The Milky Way continues to streak across the sky, though the summer portion is now giving way to the winter portion.  The fall constellations are now right in the middle of the sky.  More of the winter constellations are now up, most notably Orion the hunter in the east below Taurus.  Gemini the twins are also up in the east-northeast just below Auriga.

Interesting Stars Visible in December and January (during observatory hours)

Name / Designation Apparent Magnitude
(lower = brighter)
Distance
(light-years)
Notes
Sirius -1.44 8.6  
Vega 0.03 25  
Capella 0.08 42  
Rigel 0.18 770  
Procyon 0.4 11  
Betelgeuse 0.45 427  
Altair 0.76 17  
Aldeberan 0.87 65  
Pollux 1.16 38  
Fomalhaut 1.16 25  
Markab 1.25 140  
Deneb 1.25 3230  
Regulus 1.36 77 means "Little King"
Castor 1.58 52  
Polaris 1.97 431  
Alpheratz or Sirrah 2.07 97  
Mirach 2.07 199  
Algol 2.09 93 variable star
Enif 2.38 670  
Almak 2.1 / 5.0 & 6.3 355  triple star system w/ 64 yr orbit
Albireo 3.2 / 5.8 & 5.1 390 / 380  possibly a triple star system
Eta Cassiopeiae 3.5 / 7.4 19 480 yr orbit

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Solar System

Mercury is emerging from behind the Sun and will be visible in the evening sky in late December and early January.  Then it will pass between us and the Sun in late January.

Venus will still be visible close to the western horizon in the early evening in early December, but will pass between us and the Sun in early January.  Then it may be visible in the morning sky by the end of the month.

Mars is visible low in the morning sky, moving from Libra, through Scorpius and Ophiuchus, into Sagittarius.

Jupiter is getting lower, but remains visible in the evening sky, moving from Capricornus into Aquarius.

Saturn is also getting lower, but will be lost in the glare of the Sun by mid-January.  It is in the constellation Capricornus.

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Jupiter Great Red Spot Transits in December and January (during observatory hours)

Note: The GRS is visible on the disk of Jupiter for 50 minutes before and after meridian transit time.

Date Meridian Transit Time
12/02/21 08:19 PM
12/04/21 09:58 PM
12/09/21 09:08 PM
12/31/21 07:28 PM
01/07/22 08:17 PM

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Calendar of Night Sky Events

Date Event
12/04/21 New Moon and total solar eclipse — Not visible from Tucson.
12/10/21 First Quarter Moon.
12/13/21 Peak of Geminids meteor shower.
12/14/21 Comet Leonard predicted brightest. — Read more here.
12/18/21 Full Moon
12/21/21 Southern Solstice. — Official beginning of our winter.
01/03/21 Peak of Ursids meteor shower.
12/26/21 Last Quarter Moon.
12/28/21 Appulse of Mercury and Venus. — Separated by 4.2°
01/02/22 New Moon.
01/03/22 Peak of Quadrantids meteor shower.
01/03/22 Earth at perihelion. — Our closest approach to the Sun for the year.
01/07/22 Mercury at greatest eastern elongation. — Visible in the west after sunset.
01/08/22 Venus at inferior conjunction. — Passing between us and the Sun.
01/09/22 First Quarter Moon.
01/16/22 Pluto at conjunction. — Passing behind the Sun.
01/17/22 Full Moon.
01/23/22 Mercury at inferior conjunction. — Passing between us and the Sun.
01/25/22 Last Quarter Moon.
01/31/22 New Moon.

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Deep Sky

The summer Milky Way is now partially below the horizon at the beginning of the night, but the winter Milky Way is getting more and more prominent.  There are many open star clusters that can be seen with only binoculars scanning this part of the sky.  For example we have the asterism of the Coathanger between Aquila and Cygnus in the fainter constellation of Vulpecula.  The Pleiades (M45) is visible naked-eye in the east just above the face of Taurus which itself is another cluster called the Hyades.  We also have the Double Cluster in Perseus high in the north-northeast.  Finally, the constellation of Auriga in the northeast contains M36, M37, and M38 in close proximity.

There aren't as many globular clusters we can see this time of year, but there are still a few.  M15 is visible near the head of Pegasus in the west-southwest.  The next brightest one is M2 in Aquarius to the southwest.

For nebulae, we have several in the plane of the galaxy, one of which is the North America Nebula (C20) to the west-northwest in Cygnus.  The spectacular Orion Nebula (M42) is now just rising at the beginning of the night in the east. For planetary nebulae we have the Ring Nebula (M57) in Lyra, the Dumbell Nebula (M27) in Vulpecula, and the Blue Snowball (C22) in Andromeda.

And now the galaxies:  Our neighbor the Andromeda Galaxy (M31) is now very high in the middle of the sky and is visible on dark nights with the naked eye.  Also nearby is the Triangulum Galaxy (M33), visible with binoculars.

Interesting Deep Sky Objects to Observe during December and January (during observatory hours)

Designation Name Apparent Magnitude Apparent Size Distance
(light-years)
Type
Messier 45 Pleiades 1.6 110' 440 open cluster
Messier 31 Andromeda Galaxy 3.4 3° x 1° 2,900,000 spiral galaxy
Messier 44 Beehive Cluster 3.7 95' 577 open cluster
Messier 42 Orion Nebula 4 85' x 60' 1400-1600 diffuse nebula
Messier 33 Triangulum Galaxy 5.7 67' x 42' 3,000,000 spiral galaxy
NGC 7293 Helix Nebula 7.3 16' 450 planetary nebula
Messier 27 Dumbbell Nebula 7.4 8' × 6' 1,250 planetary nebula
NGC 7009 Saturn Nebula 8 36" 2,400 planetary nebula
Messier 81 Bode's Galaxy 8.5 21' 1,200,000 spiral galaxy
Messier 57 Ring Nebula 8.8 1' 2,300 planetary nebula
Messier 82 Cigar Galaxy 9.5 14' 1,200,000 galaxy

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Frequently Asked Questions

Why are stars different colors?

This is one of those things that for whatever reason many people are surprised to learn: Not all stars are white!  They can fall anywhere along a spectrum from red to yellow to white to blue.  The reason is temperature.  Red stars are cooler and blue stars are hotter.  The color is produced by a phenomenon known as blackbody radiation.  The gist of this concept is that everything gives off light depending on its temperature.

Most things we are used to looking at every day are not hot enough to have their blackbody radiation be visible, but if you have an infrared camera, you can easily see that warm things are in fact glowing in that part of the spectrum.  For this to start creeping into the visible range, the temperature has to be around 1000 °F.  For example, if you have an electric stovetop, it will start to glow when it reaches that temperature.

When the temperature gets up to about 2500 °F you get an orangish glow, and it passes yellow at about 6000 °F.  It then gradually turns more white until about 10000 °F, and beyond that it gets bluer.  The only things we might be used to seeing in this range would be lightning or a hot flame such as from a welding torch.

You might wonder, why are there no green or violet stars?  The reason for that is that blackbody radiation is polychromatic; that is, it emits a range of colors rather than just one.  There may be green or violet light being emitted, but it is mixed with other colors.  For example, our Sun peaks in the green part of the spectrum, but it also emits every other color, making its color appear white.

It turns out that most of the stars we can see are blue or white, because the hotter stars also tend to be brighter.  But in reality most stars in our galaxy are red.  The bright red ones we see are either close to us or are very big (giants or supergiants).  So the next time you look up at the stars, take the time to notice if you can make out the colors.

If you have any questions you'd like me to answer in the next issue of SWG, please let me know.  I'm also happy to take suggestions or comments, and also pictures if you'd like to send them.  Happy viewing!

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Date of publication:
2021