How to see the planets in the night sky, January 2021

Find out what planets will be prominent in the night sky throughout January 2020, and which bodies of the Solar System you can see tonight.

At the start of January 2021 Mars is well placed, reaching its highest position due south around 19:00 UT. From the centre of the UK this positions it 48˚ up.

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Through a telescope the mag. –0.2 planet shows a 10.4 arcsecond disc on 1 January, still large enough to show detail through an amateur telescope.

Catch Mars close to the Moon on 20 and 21 January. Credit: Pete Lawrence
Catch Mars close to the Moon on 20 and 21 January. Credit: Pete Lawrence

At present the north polar hood (NPH) should be quite evident. This is an extensive cloud covering over the planet’s north polar cap (NPC).

The now rather depleted southern cap should also be visible as a small bright patch close to the planet’s southern limb.

During January Mars will be showing a phase, appearing slightly less than 90%-illuminated.

The Red Planet has an encounter with the first quarter Moon on the evening of the 20 January, the Moon appearing 7.3˚ from the planet just before they set at around 00:30 UT on 21 January.

Later, on the evening of 21 January the now 58%-lit waxing gibbous Moon will lie 6.4˚ from Mars as darkness falls. On the evening of 21 January mag. +0.2 Mars sits 1.7˚ north of mag. +5.8 Uranus.

A view of the Moon and Mars as they will appear from the southwest of England, 21 January 2021, 10pm UTC. Credit: Stellarium
A view of the Moon and Mars as they will appear from the southwest of England, 21 January 2021, 10pm UTC. Credit: Stellarium

As the month progresses, Mars moves east, slipping from the constellation of Pisces into Aries, reducing in brightness and apparent size as it goes.

By the end of the month Mars shines at mag. +0.4 and presents a telescopic disc which appears 7.9 arcseconds across.

Mars will move slightly further towards the north throughout the month, exceeding Uranus’s declination on 11 January to become the most northerly planet currently in our sky.

At the end of January, against a background of darkening twilight, mag. +0.4 Mars is 54˚ up when due south at 18:05 UT. Although smaller than of late, the higher altitude will assist in stabilising our view of this enigmatic planet.

See Jupiter, Saturn and Mercury

Following the Great Conjunction on 21 December, evening planets Jupiter and Saturn remain close during January but their visibility degrades as they slip ever closer towards the Sun, Saturn reaching solar conjunction on 24 January.

This date marks Saturn’s transition from the evening sky into the morning sky.

In 2020, Jupiter lay west of Saturn. After the Great Conjunction the planets swap sides and Saturn will be lying west of Jupiter.

Jupiter is the brighter of the pair at mag. –1.8 and is the first to appear after sunset, typically visible from around 30 minutes after the Sun has dropped below the horizon.

Mag. +0.9 Saturn is still pretty close at the start of January and should be fairly easy to pick out as the sky continues to darken.

Follow the ever-changing geometric patterns formed by the planets Mercury, Jupiter and Saturn after 9 January. They are joined by a waxing crescent Moon on 14 January 2021. Credit: Pete Lawrence
Follow the ever-changing geometric patterns formed by the planets Mercury, Jupiter and Saturn after 9 January. They are joined by a waxing crescent Moon on 14 January 2021. Credit: Pete Lawrence

From 7 January, the pair are joined by Mercury. Located closer to the Sun on 7 January, Mercury has the advantage of being relatively bright itself at mag. –0.9.

From 9 January until 13 January, Mercury, Jupiter and Saturn remain close, forming an ever-changing geometric pattern as the swifter inner planet appears to zip past the lumbering gas giants. By 13 January, Mercury will still be bright at mag. –0.8.

On 14 January, Saturn will become tricky to spot unless you have a flat southwest horizon. On this date, Mercury, Jupiter and Saturn will be joined by a slender 2%-lit waxing crescent Moon.

The Moon will be on par with the altitude of Mercury, the higher of the three planets, and located 4.5˚ further to the southeast.

As Jupiter and Saturn are lost in the Sun’s glare, Mercury continues to creep east towards a favourable eastern elongation on 24 January.

The phase and relative sizes of the planets, January 2021. Each planet is shown with south at the top, to show its orientation through a telescope. Credit: Pete Lawrence.
The phase and relative sizes of the planets, January 2021. Each planet is shown with south at the top, to show its orientation through a telescope. Credit: Pete Lawrence.

The best planets to see in January 2021

Mars

  • Best time to see 1 January, 19:00 UT
  • Altitude 48˚
  • Location Pisces
  • Direction South
  • Features Albedo markings, polar caps, weather
  • Recommended equipment 150mm telescope or larger

Mercury

  • Best time to see 24 January, 30 minutes after sunset
  • Altitude 9˚ (low)
  • Location Capricornus
  • Direction Southwest

Too close to the Sun in the evening sky, Mercury is difficult to see at January’s start. After 7 January it’s visible 30 minutes after sunset close to Jupiter and Saturn.

Greatest eastern elongation occurs on 24 January as mag. –0.5 Mercury sets 100 minutes after the Sun. By 31 January, although remaining above the horizon for 90 minutes after sunset, it will be mag. +1.1.

Venus

  • Best time to see 1 January, 30 minutes before sunrise
  • Altitude 6˚ (low)
  • Location Ophiuchus
  • Direction Southeast

Venus is a morning planet rising 1.5 hours before the Sun on 1 January, 55 minutes before on the 15 January and 26 minutes before on 31 January. A 4%-lit waning crescent Moon lies 6˚ west of mag. –3.9 Venus on 11 January.

Jupiter

  • Best time to see 10 January, 30 minutes after sunset
  • Altitude 5˚ (low)
  • Location Capricornus
  • Direction Southwest

Jupiter and Saturn remain close; they begin the month near the Sun, but are then lost in solar glare. Both are visible low above the southwest horizon 30 minutes after sunset at January’s start. As Jupiter and Saturn slip toward the Sun, Mercury joins them.

On 9 January mag. –0.8 Mercury appears 3.2˚ from Jupiter, while on 10 Janaury Mercury forms an equilateral triangle with Jupiter and Saturn.

On 11 January Mercury forms a right-angled triangle with Jupiter and Saturn, 1.4˚ from Jupiter. Solar conjunction for Jupiter occurs on 28 January.

Saturn

  • Best time to see 10 January, 30 minutes after sunset
  • Altitude 3˚ (very low)
  • Location Capricornus
  • Direction Southwest

Saturn is close to Jupiter at the month’s start, appearing 1.3˚ away on 1 January. As January progresses, this apparent separation increases. Mercury joins the pair between 8–13 January, but Saturn is the fainter of the three. On 24 January, Saturn is in conjunction with the Sun.

Uranus

  • Best time to see 1 January, 19:40 UT
  • Altitude 50˚
  • Location Aries
  • Direction South

Uranus is a mag. +5.7 evening planet in Aries. On 1 January Mars lies 9.2˚ to its west-southwest. The planets appear to converge so that by 19 January, they are 1.7˚ apart. A 58%-lit waxing gibbous Moon joins the scene on the evening of 21 January.

Neptune

  • Best time to see 1 January, 18:15 UT
  • Altitude 29˚
  • Location Aquarius
  • Direction South-southwest

At the start of 2021 we find Neptune compromised because of its position within Aquarius, unable to be seen at its highest point in the sky under truly dark conditions. The planet appears 27˚ above the west-southwest horizon when darkness falls on 1 January.

As we head toward the month’s end, we find that it can only achieve an altitude of 13˚ above the west-southwest horizon at true darkness.

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Pete Lawrence is an experienced astronomer and a co-host of The Sky at Night. This guide originally appeared in the January 2021 issue of BBC Sky at Night Magazine.