How to see the planets: March 2021

Catch a last glimpse of Mars in March as our view of the Red Planet begins to deteriorate. Find out how to see it and other planets in the night sky this month.

Mars begins March 2021 located near the Pleiades open cluster. Credit: BBC Sky at Night Magazine.

As far as the UK is concerned, the planets are rather poorly-placed at present, all but Mars being hampered by their proximity to the Sun in the sky.

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However, despite currently being the most northerly planet, the appearance of Mars continues to deteriorate, it being unable to reach its highest position in the sky in darkness.

At the start of March, Mars shines at mag. +0.9 and presents a diminishing disc 6.4 arcseconds across through the eyepiece.

By the end of March, the Red Planet will have dimmed further to mag. +1.3 and through the eyepiece of a telescope shrinks to 5.3 arcseconds.

It tracks east throughout the month, passing across the northern part of the constellation of Taurus, the Bull.

At the beginning of March, Mars is located south of the Pleiades open cluster, M45, lying 2.5˚ from the cluster on 4 March.

For more events like this, read our regularly-updated guide to upcoming conjunctions or listen to our monthly Star Diary podcast

Mars makes its closest approach to the Pleiades on 3 March. Credit: Pete Lawrence
Mars makes its closest approach to the Pleiades on 3 March. Credit: Pete Lawrence

Mars sits 7˚ north of orange giant Aldebaran on the evening of 19 March, the date when the planet has its monthly visit from the Moon.

On this occasion, the Moon will be visible between Mars and Aldebaran, roughly one third of the way along the line joining both objects, starting from the planet.

The Moon will appear as a 33%-lit waxing crescent on this date.

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Mars between Pleiades and Aldebaran. 8 March 2021
Mars sits between the Pleiades and Aldebaran on 8 March 2021. Credit: Stellarium

The small appearance of Mars’s disc through the eyepiece is down to an increase in distance between Earth and the Red Planet.

Having enjoyed an excellent opposition last October, Mars is now entering a slow period where it’s too small for serious observation.

The next opposition occurs on 8 December 2022, when Mars reaches 17 arcseconds across and gets to a good declination for the UK in Taurus.

Although smaller in maximum diameter than the 2020 opposition, in 2022, Mars attains an altitude of over 60˚ when due south.

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

Planets to look out for in March 2021:

Mars

  • Best time to see 1 March, 19:20 UT
  • Altitude 50˚
  • Location Taurus
  • Direction Southwest
  • Features Albedo markings, polar ice caps, weather
  • Recommended equipment 150mm or larger

Mercury

  • Best time to see 6 March, from 30 minutes before sunrise
  • Altitude 1˚ (extremely low)
  • Location Capricornus
  • Direction East-southeast

Mercury is poorly placed in the morning sky all month, despite reaching greatest western elongation on 6 March. For more on what this means, read our guide to inferior and superior planets. Jupiter, Saturn and Mercury appear together this month. On 5 March, mag. +0.2 Mercury lies 19.5 arcminutes from mag. –1.8 Jupiter while mag. +0.9 Saturn lies 8.8˚ to the west.

On 10 March, Mercury lies 4.3˚ east of Jupiter with a 10%-lit waning crescent Moon sitting 11˚ to Mercury’s southwest. The Moon rises 30 minutes before the Sun on this date, Mercury appearing 10 minutes before the Moon, but you’ll find the bright morning twilight will make this a tricky observation.

Venus

Venus reaches superior conjunction on 26 March when it transitions from being a morning to an evening planet. Despite this and a favourable steep ecliptic angle in the west after sunset, Venus is unlikely to be seen throughout March.

Jupiter

  • Best time to see 31 March, 40 minutes before sunrise
  • Altitude 4˚ (very low)
  • Location Capricornus
  • Direction East-southeast

Jupiter rises approximately 45 minutes before the Sun at the start of March, but a shallow ecliptic angle with the eastern sunrise sky at this time of year keeps its location is poor.

During March in the morning sky at sunrise, Jupiter just doesn’t achieve sufficient altitude to be easily observable. It has a very close encounter with mag. +0.2 Mercury on 5 March, both planets separated by just 19 arcminutes as they pop up above the east-southeast horizon. 

10%-lit waning crescent Moon joins the scene on 10 March, but is more poorly placed than Jupiter! On 31 March, despite rising 70 minutes before the Sun, Jupiter doesn’t quite make 9˚ above the horizon before sunrise.

Saturn

  • Best time to see 31 March, 50 minutes before sunrise
  • Altitude 3˚ (very low)
  • Location Capricornus
  • Direction Southeast

During March, Saturn can be seen crawling further from the Sun in the morning sky, but despite this the planet remains low. It appears 8˚ to the west of Jupiter on 1 March, a separation that increases to 12˚ by the month’s end. 

17%-lit waning crescent Moon sits to the west-southwest of Saturn on the morning of 9 March. At the month’s end Saturn attains an altitude of 8˚ above the southeast horizon before the onset of morning twilight.

Uranus

  • Best time to see 1 March, 19:40 UT
  • Altitude 30˚
  • Location Aries
  • Direction West-southwest

The observing window for Uranus closes during March as the evening twilight expands to engulf this distant world. Located in southern Aries, Uranus appears 30˚ up as true darkness falls at March’s start. By the end of March it has an altitude of less than 5˚ by the time true darkness arrives.

Neptune

Not visible this month – solar conjunction on 10 March.

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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 March 2020 issue of BBC Sky at Night Magazine.