Watch a video summary of the January 2021 guide to the bright planets:
Jupiter and Saturn come out at evening dusk in early January, yet lurk quite low in the sky. Moreover, they follow the sun beneath the horizon before nightfall. Day by day, the twosome appears a bit lower in the sky at dusk, and sets sooner after sundown. For the best view of these worlds, find an unobstructed horizon in the direction of sunset, and seek them out about 45 to 60 minutes after the sun goes down with either the eye alone or binoculars. Both of these worlds will disappear from the evening sky during the second half of January, as they transition out of the evening sky and into the morning sky.
Around the world, Jupiter and Saturn set about 1 1/2 hours after the sun in early January. That’ll taper to 1/2 hour or so by mid-month.
Have binoculars handy for this month’s planetary trio, or three planets congregating together on the sky’s dome! Day by day, as Jupiter and Saturn sink downward, toward the setting sun, Mercury will be climbing out of the afterglow of sunset. Mercury will meet up with Saturn for a conjunction on January 9, and then rendezvous with Jupiter for a slightly closer conjunction on January 11. These three planets will be out at evening dusk, but will set before nightfall, so you’ll need an unobstructed horizon to spot their furtive gathering in the evening twilight. Read more.
Look first for brilliant Jupiter; Saturn is the bright object immediately above Jupiter. Although Saturn is easily as bright as a 1st-magnitude star – as bright as the brightest stars in our sky – the ringed planet can’t compete with the the king planet Jupiter, which outshines Saturn by some 11 times. After all, Jupiter ranks as the fourth brightest celestial object, after the sun, the moon and the planet Venus, respectively. (But there’s no way to mistake Jupiter for Venus, or vice versa, because Jupiter is out at evening dusk, whereas Venus is out at morning dawn.)
Mars is the only bright planet that’s out at nightfall and the evening hours throughout January 2021. The three other evening planets – Mercury, Jupiter and Saturn – only appear at evening dusk (if at all) and exit the sky by nightfall. Mars is highest up for the night at nightfall and slowly descends westward during the evening hours, finally setting in the west at or around midnight. Its ruddy starlike presence still lights up our evening sky, although in the months ahead, Mars will slowly but surely dim.
Modestly-bright Mars remains an easy object to see with the eye alone throughout January. Let the moon help guide your eye to Mars for several nights centered on or near January 20.
Venus – the brightest planet – reached its greatest elongation from the sun in the morning sky on August 12 or 13 (depending upon your time zone). As January 2021 opens, however, Venus appears much closer to the sun than it did some months ago. Venus’ angular distance from the sun – its distance from the sun on our sky’s dome – shrinks throughout January. Day by day, watch for Venus to sink deeper and deeper into the morning twilight.
At mid-northern latitudes, Venus rises about 1 1/2 hours before the sun in early January, tapering down to about 35 minutes by the month’s end.
At and near the equator, Venus rises 1 1/2 hours before the sun in early January, decreasing to 55 minutes by the month’s end.
At temperate latitudes in the Southern Hemisphere, Venus rises 1 1/2 hours before the sun in early January, and around 1 hour by the month’s end.
Why is Venus getting so close to the sunrise now, as seen from Earth? The answer is that Venus – in its smaller and faster orbit around the sun – is about to “turn the corner” ahead of us in orbit. In other words, Venus is about to pass on the far side of the sun from Earth. Its faster motion around the sun relative to Earth will bring the sun between us and it. Venus will be gone from our sky from about late February to perhaps late April. It will be most nearly behind the sun, at superior conjunction as viewed from Earth, on March 26. It will return to the evening sky in earnest in May, appearing near the western horizon as a surprisingly bright evening “star.”
As viewed through the telescope in January 2021, Venus’ waxing gibbous phase will widen, yet its overall disk size will shrink. Venus’ disk is 94% illuminated in early January, and 97% illuminated near the month’s end; Venus’ angular diameter, on the other hand, will shrink to about 94% of its initial size by the end of January.
Watch for the waning crescent moon to shine with Venus in the morning sky for several days, centered around January 11.
Mercury is nominally an evening object all month long in January. However, this world sits quite close to the afterglow of sunset in early January, and probably won’t be visible in the evening twilight until after the first week of January.
Day by day, as Mercury climbs away from the setting sun, the planets Jupiter and Saturn sink sunward. All three planets – Mercury, Jupiter and Saturn – will appear in nearly the same spot on the great dome of sky for several days, centered on January 10. Dazzling Jupiter – the fourth-brightest celestial object in all the heavens – is your ticket to finding Mercury and Saturn. Bring along your binoculars, find an unobstructed western horizon and start your search no later than 45 minutes after sunset. Read more.
Mercury will have a conjunction with Saturn on January 9, and then a conjunction with Jupiter on January 11. Between these two dates – on January 10 – these three planets will snuggle up most closely on the sky’s dome for the month, fitting inside a circle measuring 2.4 degrees in diameter. (For reference, the width of a finger at arm’s length spans about 2 degrees of sky.) A grouping of three planets in a circle whose diameter spans 5 degrees or less is known as a planetary trio.
The most recent planetary trio last took place on October 26, 2015. Next month, we’ll have one in the morning sky on February 13, 2021. After that, the next planetary trio won’t occur until April 20, 2026.
Starting around mid-month, as Jupiter and Saturn fade into the sun’s glare, Mercury should become more easily visible to the eye alone in the evening sky. Use the moon to help you locate Mercury on January 14, 15 and 16.
Best yet, perhaps, watch for Mercury around the time of its greatest elongation from the setting sun on January 23. At mid-northern latitudes, Mercury stays out a whopping 90 minutes after sunset, providing you with a great opportunity to spot the solar system’s innermost planet!
What do we mean by bright planet? By bright planet, we mean any solar system planet that is easily visible without an optical aid and that has been watched by our ancestors since time immemorial. In their outward order from the sun, the five bright planets are Mercury, Venus, Mars, Jupiter and Saturn. These planets actually do appear bright in our sky. They are typically as bright as – or brighter than – the brightest stars. Plus, these relatively nearby worlds tend to shine with a steadier light than the distant, twinkling stars. You can spot them, and come to know them as faithful friends, if you try.
Bottom line: January starts out the month with two bright planets at dusk, Jupiter and Saturn, which then team up with Mercury to showcase a spectacularly-close threesome at dusk January 10. Mars is the only bright planet to light up the evening hours after nightfall. Dazzling Venus, the sole bright morning planet, rises in the east at dawn.
Bruce McClure has served as lead writer for EarthSky's popular Tonight pages since 2004. He's a sundial aficionado, whose love for the heavens has taken him to Lake Titicaca in Bolivia and sailing in the North Atlantic, where he earned his celestial navigation certificate through the School of Ocean Sailing and Navigation. He also writes and hosts public astronomy programs and planetarium programs in and around his home in upstate New York.