Closest Mars-Pleiades conjunction until 2038

This year – on March 3, 2021 – the red planet Mars and the Pleiades star cluster – also known as the Seven Sisters – stage their closest conjunction on the sky’s dome until February 4, 2038. Mars swings 2.6 degrees south of the Pleiades. That’s the closest Mars-Pleiades conjunction since January 20, 1991, when Mars passed 1.7 degrees south of the Pleiades. Looking ahead – after March 3, 2021 – a closer conjunction of Mars and the Pleiades won’t happen again until February 4, 2038, when Mars will swing 2.0 degrees south of the Pleiades.

No matter where you live worldwide, look for Mars and the Pleiades at nightfall and early evening, for that’s when the dynamic twosome is highest up for the night. Mars and the Pleiades sink westward as evening deepens into late night, so it might be best to spot the close encounter at early evening. The celestial couple stays out until around midnight at mid-northern latitudes, or mid-evening at temperate latitudes in the Southern Hemisphere.

Using Orion's Belt to find the star Aldebaran and the Pleiades cluster.

Use Orion’s Belt to star-hop to the constellation Taurus the Bull. During the first week of March 2021, look for the red planet Mars and the Pleiades cluster to snuggle up quite close together on the sky’s dome. Have binoculars? For a big treat, enjoy an eyeful of the Pleiades cluster!

If you’re familiar with the constellation of Orion the Hunter, use this bright and beautiful constellation to star-hop to Mars and the Pleiades. Find the three moderately-bright stars of Orion’s Belt, and extend Orion’s Belt westward to the constellation Taurus the Bull. Taurus’ two most notable signposts consist of the red star Aldebaran and the Pleiades star cluster, and – in March 2021 – the red planet Mars.

Chart showing constellations Orion and Taurus.

The 3 stars at the midsection of Orion – called the Belt of Orion – always point to the bright red star Aldebaran, in the V-shaped head of Taurus the Bull. Chart via Wikipedia.

At present, there are two bright ruddy “stars” in the constellation Taurus the Bull: the star Aldebaran and the planet Mars. It is fairly easy to distinguish Mars from Aldebaran, despite their similarity in color and brightness, because the red “star” appearing much closer to the Pleiades star cluster is none other than Mars.

Aldebaran shines by its own light whereas Mars shines by reflecting the light of the sun. Aldebaran and the stars of the Pleiades cluster represent “fixed” points of light in the constellation Taurus the Bull. Mars, on the other hand, is a temporary visitor, passing 2.6 degrees south of the Pleiades cluster on March 3, at 23:26 UTC. This presents Mars’ closest pass to the Pleiades cluster until February 4, 2038.

Do you have binoculars? A typical binocular field spans some 5 degrees of sky, so Mars and the Pleiades cluster should readily fit within a single binocular field for at least several days, if not close to a week. If you’ve never viewed the Pleiades cluster through binoculars, you’re missing out on one of the sky’s most magnificent treasures. Most people can see six Pleiades stars with the eye alone, but binoculars dramatically increase the number of Pleiades stars that you can see.

A red starlike point, Mars, next to a bluish dipper-shaped star cluster, the Pleiades.

View at EarthSky Community Photos. | Abhijit Patil caught red Mars and the dipper-shaped Pleiades star cluster – aka the Seven Sisters – on April 1, 2019. Thank you, Abhijit! The previous Mars-Pleiades conjunction happened on March 31, 2019.

In early March 2021, Aldebaran might appear a touch brighter than Mars to the eye. Mars is dimming somewhat by the day, and will probably be obviously fainter than Aldebaran by the time Mars passes 7 degrees north of Aldebaran on March 20, 2021. By April 24, 2021, Mars will be fainter yet when it passes out of the constellation Taurus and into the constellation Gemini the Twins.

Mars, the 4th planet form the sun, takes nearly two Earth-years to travel full circle through the constellations of the zodiac. Mars normally laps the Pleiades cluster every other year. However, as an exception, Mars’ next conjunction with the Pleiades will happen next year (instead of the year after): August 20, 2022. That’s because this year’s conjunction happens fairly early in the year, and, in addition, no intervening Martian retrograde takes place between the 2021 and 2022 Mars-Pleiades conjunctions. After 2022, Mars-Pleiades conjunctions will happen every other year until March 14, 2036.

Mars-Pleiades conjunctions

Mar 03, 2021 (Mars 2.6 degrees south of the Pleiades)
Aug 20, 2022 (Mars 5.4 degrees south of the Pleiades)
Jul 20, 2024 (Mars 4.7 degrees south of the Pleiades)
Jun 28, 2026 (Mars 4.4 degrees south of the Pleiades)
Jun 07, 2028 (Mars 4.1 degrees south of the Pleiades)
May 19, 2030 (Mars 3.7 degrees south of the Pleiades)
Apr 28, 2032 (Mars 3.6 degrees south of the Pleiades)
Apr 08, 2034 (Mars 3.3 degrees south of the Pleiades)
Mar 14, 2036 (Mars 2.9 degrees south of the Pleiades)

Source: Sky Event Almanacs

In rare instances, Mars can have three conjunctions with the Pleiades cluster in period of about 4.7 months. But for this to happen, Mars must reach opposition at a critical time, so that Mars can swing by the Pleiades going in prograde (eastward in front of the background stars of the zodiac), then in retrograde (westward in front of the backdrop stars), and then in prograde (eastward) again. This last happened 1990-91 and will next happen in in 2037-38.

1990-91:
First conjunction: August 31, 1990 (5.8 degrees, going eastward)
Second conjunction: December 14, 1990 (2.0 degrees, going westward)
Third conjunction: January 20, 1991 (1.7 degrees, going eastward)
Martian opposition: November 27, 1990

2037-38:
First conjunction: September 12, 2037 (6.0 degrees, going eastward)
Second conjunction: November 13, 2037 (3.7 degrees, going westward)
Third conjunction: February 4, 2038 (2.0 degrees, going eastward)
Martian opposition:November 19, 2037

This year – on March 3, 2021 – gives us the closest Mars-Pleiades conjunction since January 20, 1991. Enjoy an eyeful of the glorious encounter while the time is still at hand, because a closer Mars-Pleiades conjunction won’t be in the works again until February 4, 2038.

Bruce McClure