Uranus-Jan2021
Uranus, January 2021 (Chris Vaughan, Starry Night Education)

January 2021: Planets at a glance

This month, Uranus completes its retrograde loop and resumes its eastward motion in the skies, and Mercury returns to view. Here’s more on the planetary events this month.

Listen to the story

For those of you who like to listen to your stories, click below to hear Susan Trishel Monsøn reading Chris Vaughan’s summary of the planets for January.

Mercury

Mercury, January 2021 (Chris Vaughan, Starry Night Education)

Following its December, 2020 solar conjunction, Mercury will return to view in the southwestern evening sky after the first week of January. This apparition will be a very good one for observers located at mid-Northern latitudes. From January 9 to 12, Mercury will climb past bright Jupiter and rather faint Saturn. The best viewing times for that planet grouping will be a short period after 5:30 p.m. local time, but you’ll need an unobstructed horizon to see them. On January 14, the crescent Moon will be positioned a fist’s diameter to the upper left (or 10 degrees to the celestial southeast) of Jupiter, with dimmer Mercury midway between them, setting up a lovely photo opportunity. On the evening of January 23 in the Americas, Mercury will reach its widest separation, 19 degrees east of the Sun, and maximum visibility, particularly between 5:30 and 6:30 p.m. local time. Viewed in a telescope during the month, Mercury’s illuminated phase will wane from nearly full to a thin crescent as it moves between Earth and the Sun, and its apparent disk size will swell from 5 to 9 arc-seconds. Over the same time period, Mercury will decrease in brightness.

Venus

Venus, January 2021 (Chris Vaughan, Starry Night Education)

During January, Venus will remain visible as a very bright, magnitude -3.9 object sitting low over the southeastern horizon before sunrise. Because Venus will be swinging sunward, that viewing window will decrease from 90 minutes on January 1 to only half an hour at month-end. On January 11, the old crescent Moon will sit a few finger widths to the right (or 3-4 degrees to the celestial southwest) of Venus, making a nice photo opportunity when composed with some interesting scenery.

Mars

Mars, January 2021 (Chris Vaughan, Starry Night Education)

Mars will continue to be conveniently positioned for observing from dusk until an hour after midnight during January, but it will be far fainter and smaller than it was during October’s opposition. Mars will be at its maximum elevation, more than halfway up the southern sky, right after dusk, and then it will descend as it’s carried west by Earth’s rotation. Because Earth will continue to increasing our distance from Mars, the Red Planet will diminish in brilliance by almost half this month, fading from magnitude –0.22 on January 1 to magnitude +0.44 on January 31. Telescope views of the planet will show Mars’ apparent disk diameter shrinking from 10 to 8 arc-seconds. On January 5, Mars’ eastward motion will carry it from Pisces to western Aries, which it will traverse for the rest of the month. On January 20, Mars will pass only 1.6 degrees to the north of magnitude 5.76 Uranus, outshining the blue-green planet by a factor of 164. That same evening, the waxing, half-illuminated Moon will be positioned 7 degrees to the southwest of the two planets.

Jupiter

Jupiter, January 2021 (Chris Vaughan, Starry Night Education)

A terrific season of Jupiter viewing will end in January. During the first half of the month the bright, magnitude -1.95 planet will appear above the southwestern horizon for a short time after sunset, but it will become more entrenched within the evening twilight with each passing day. One-tenth as bright Saturn will sit only 2 degrees below (or to the celestial west) of Jupiter all month long. Mercury will climb past Jupiter on January 10-12, and the young crescent Moon will join those planets on January 14. Jupiter will disappear by month end and then reach solar conjunction on January 29.

Saturn

Saturn, January 2021 (Chris Vaughan, Starry Night Education)

Being 11 times fainter than Jupiter, Saturn will be lost to view in the southwestern twilight after the opening week of January. If you can find Jupiter, binoculars might show you the ringed planet sitting less than 2 degrees to Jupiter’s lower right. Saturn will reach solar conjunction on January 24, five days before Jupiter.

Uranus

Uranus, January 2021 (Chris Vaughan, Starry Night Education)

On January 14, magnitude 5.75 Uranus will complete a retrograde loop that began in mid-August. On that date it will temporarily cease its westward motion through the distant stars of southwestern Aries before resuming its regular eastward motion. During January, the blue-green planet will be conveniently positioned for observing after dusk, when it will be at its maximum elevation more than halfway up the southern sky until an hour after midnight. Telescope views of the planet will show its tiny 3.6 arc-seconds wide disk. You can use Mars to find Uranus in the same binoculars field of view from January 10 to 25. On January 20, Mars will sit only 1.6 degrees to the north of Uranus, outshining the blue-green planet by a factor of 164. That same evening, the waxing, half-illuminated Moon will pass the two planets. The Moon will remain close to them on January 21. Use the moonless first half of January to try seeing the magnitude 5.7 planet with unaided eyes or binoculars.

Neptune

Neptune, January 2021 (Chris Vaughan, Starry Night Education)

Neptune will be available for observing in the early evening sky during January. From dark sky locations the magnitude 7.9 planet can be observed in good binoculars and backyard telescopes. Look in eastern Aquarius, about 1 degree to the east of the medium-bright star Phi Aquarii, or φ Aqr. Both the planet and that star will appear together in the field of view of a telescope at low magnification. The best time to view the distant planet will be as soon as the sky darkens fully, when the planet will be about one-third of the way up the southwestern sky. By month-end, Neptune will be rather low in the west by the time the sky darkens enough to see it.

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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