See Mars pass the Pleiades star cluster this month

Mars passes south of the Pleiades cluster, February - March 2021, making for a beautiful night-sky sight. Here's all you need to know to spot this conjunction.

Over February – March 2021, the planet Mars will be passing south of the beautiful, blue open cluster M45, also known as the Pleiades or Seven Sisters, making for a fantastic night-sky observing or astrophotography target.

Advertisement

The best time to see it will be 1-5 March, with closest approach on 3 March and the Moon nearby on 19 March, but you can start observing the two as we approach the end of February.

It would also make a good composite astrophoto showing the planet in motion across the night sky.

Mars appears next to the Pleiades, 30 March 2019. Photo by: Alan Dyer/VW PICS/Universal Images Group via Getty Images
Mars appears next to the Pleiades, 30 March 2019. Photo by Alan Dyer/VW PICS/Universal Images Group via Getty Images

In this guide we’ll reveal when this Mars-Pleiades conjunction is happening, what you can see in the night sky leading up to it, and dates for when it will look at its best.

Mars’s mag. +0.5 brightness at the start of February was a far cry from the brilliant mag. –2.6 it got to in October 2020, yet the Red Planet will still be interesting to watch with the naked eye over February to March because of this close encounter with the Pleiades cluster.

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

The Pleiades Stephen Tolley, Liskeard, Cornwall, 19 January 2020 Equipment: Nikon D600 DSLR, Tamron 150-600mm lens, Celestron AVX mount
The Pleiades photographed by Stephen Tolley, Liskeard, Cornwall, 19 January 2020. Equipment: Nikon D600 DSLR, Tamron 150-600mm lens, Celestron AVX mount

Observing Mars in February 2021

At the start of February 2021 Mars was in southern Aries, approximately mid-way between Hamal (Alpha (α) Arietis) and Menkar (Alpha (α) Ceti). As February slips by, Mars nudges further east.

On the evening of 16 February, mag. +0.7 Mars passed 27 arcminutes south of mag. +4.3 Delta (δ) Arietis. A 40%-lit waxing crescent Moon joined Mars on the evening of 18 February, the Moon’s disc being 5˚ below the planet early in the evening.

Mars moves from Aries into Taurus on 23/24 February but is unable to reach its highest position in the sky, due south in darkness. Despite this, it remains the most northerly planet, managing to appear 55˚ up as darkness falls.

As we approach the end of February, Mars appears near the Pleiades open cluster. Early evening on 28 February the mag. +0.9 Red Planet sits just 3.4˚ south of this beautiful cluster.

Mars will appear close to the Pleiades open cluster at the end of February 2021. Credit: Pete Lawrence.
Mars will appear close to the Pleiades open cluster at the end of February 2021. Credit: Pete Lawrence.

Observing Mars in March 2021

At the start of March, Mars is located 3˚ south of the Pleiades. As it tracks east, Mars also moves slightly north against the background stars. This apparent motion means the planet appears closest to the cluster on the evening of 3 March, the separation distance being around 2.5˚ on this date.

Mars will appear at mag. +1.0 on 3 March, and its proximity to the Pleiades will make for a wonderful target to observe in the night sky during the early part of the month.

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

How to observe the Mars Pleiades conjunction

Binoculars are perfect for watching this conjunction. Mars and the Pleiades will easily fit in the same field of view for typical amateur mid-power binoculars.

In addition, the large size of the Pleiades suits such an instrument. Where a telescope tends to look through the Pleiades, binoculars reveal many of the fainter stars associated with the star cluster while managing to contain it all in a single view.

The conjunction will also be attractive for astro imaging: both objects are bright enough to register on many devices ranging from some smartphones to DSLRs and MILCs. A lens of 200mm focal length combined with a non full-frame DSLR (eg APS-C) will record both objects well.

For more on this, read our guide on how to photograph a conjunction.

Enter the Hyades

Keep an eye on Mars and watch out for the Hyades cluster on 19 March 2021. Credit: Pete Lawrence
Keep an eye on Mars and watch out for the Hyades cluster on 19 March 2021. Credit: Pete Lawrence

As we head into the second week of March, Mars will have moved east far enough to sit between the Pleiades and the V-shaped Hyades.

The Hyades is an old cluster, the closest to Earth at a distance of 150 lightyears. Estimates put the age of the Hyades at 625 million years, and this explains why its stars appear less vibrant than the 100 million-year-old Pleiades.

The distance to the Pleiades is around 444 lightyears, making it appear far more compact than the spread-out Hyades.

A 50mm lens on a non-full frame DSLR will capture both clusters and Mars in the same frame. For an added bonus, on 19 March a 32%-lit waxing crescent Moon will sit 2.3˚ to the south of Mars, between the planet and the northmost star in the main Hyades pattern, Ain (Epsilon (ε) Tauri).

Did you manage to observe or photograph the Mars-Pleiades conjunction? Let us know by contacting us via contactus@skyatnightmagazine.com.

Advertisement

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