2021, March 31: PM Arcturus, Mars, Moon

2021, March 31: Arcturus rises in the east-northeast at sunset. It lies low in the east-northeast an hour after sunset.
2021, March 31: Arcturus rises in the east-northeast at sunset. It lies low in the east-northeast an hour after sunset.

March 31, 2021: Arcturus rises at sunset and can be found low in the east-northeast an hour later.  Mars marches eastward in front of the stars of Taurus.  The bright gibbous moon rises low in the east-southeast near midnight.

by Jeffrey L. Hunt

Chicago, Illinois:  Sunrise, 6:35 a.m. CDT; Sunset, 7:15 p.m. CDT.  Check local sources for sunrise and sunset times for your location.

The bright star Arcturus, “the bear guard,” rises at sunset.  An hour after sunset, find it about 10° up in the east-northeast.

Arcturus is the third brightest star visible in the skies of Earth, and it is the brightest in the northern half of the sky. The star is part of Boötes, the Herdsman.  In some artwork, Boötes is chasing after the Big Bear, Ursa Major.

The constellation’s pattern resembles a kite.  It is better seen when the star and the pattern are higher in the sky.  This evening it lies along the horizon to the left of Arcturus.

Unlike planets that rise at sunset, Arcturus is far north of the plane of the solar system. It appears in the sky for over 14.5 hours, compared to the 12.7 hours of daylight. 

The farther north a celestial object, the longer it stays in the sky. When the sun rises and sets north of the equator, the days are longer than it is south of the equator.

Arcturus is south a few hours after midnight.  As morning twilight begins, the star is over two-thirds of the way up in the sky in the southwest.

2021, March 31: After sunset find Mars above the “V” of Taurus and below the Bull’s horns.
2021, March 31: After sunset find Mars above the “V” of Taurus and below the Bull’s horns.

Mars is the lone bright evening planet.  It is over halfway up in the west, above the “V” of Taurus, made by Aldebaran and the Hyades star cluster.  The planet moved nearly 18° eastward during the month.

Mars is moving toward the Bull’s horns, marked by Elnath and Zeta Tauri (ζ Tau).  This evening the planet is 7.4° below Elnath.

2021, March 31: Through a binocular, Mars is 4.1° to the upper left of Tau Tauri (τ Tau) and 2.7° to the upper right of Iota Tauri (ι Tau).
2021, March 31: Through a binocular, Mars is 4.1° to the upper left of Tau Tauri (τ Tau) and 2.7° to the upper right of Iota Tauri (ι Tau).

Use a binocular to find the starry background with Mars.  This evening, the Red Planet is 4.1° to the upper left of Tau Tauri (τ Tau) and 2.7° to the upper right of Iota Tauri (ι Tau). 

2021, March 31: As midnight approaches the moon is low in the east-southeast, below the claws of the scorpion.
2021, March 31: As midnight approaches the moon is low in the east-southeast, below the claws of the scorpion.

As midnight approaches, the bright moon is about 5° above the east-southeast horizon, 13.0° below Zubeneschamali, “the northern claw” of the scorpion.

Here’s more about Mars during 2021.

Read about Mars during March.

Detailed Note: One hour before sunrise, the bright gibbous moon (18.0d, 90%) is nearly 25° up in the southwest, 2.6° to the upper left of Zubenelgenubi. Farther eastward, Saturn is over 12° above the southeastern horizon.  Jupiter – over 7° in altitude above the east-southeastern horizon – is 11.7° of ecliptic longitude east of Saturn. Use a binocular to see the planets against the starry background.  Saturn is 2.8° to the upper right of θ Cap, while Jupiter is 5.2° to the lower left of ι Cap. You may have already spotted Nashira (“the lucky star of the verdant fields at the end of summer,” γ Cap, m = 3.6) and Deneb Algiedi (“the kid’s tail, δ Cap, m = 2.8) below Jupiter.  The planet and the stars make a nice triangle.  Jupiter is 2.1° to the upper left of Nashira and 2.0° above Deneb Algedi.  Arcturus (“the bear-guard,” α Boo, m = −0.1) rises at sunset.  One hour after sunset, Mars is less than 50° up in the west, in Taurus above the “V” made by Aldebaran and the Hyades star cluster.  The planet moved eastward 17.7° during the month.  Use a binocular to spot it 4.1° to the upper left of τ Tau, 2.7° to the upper right of ι Tau, and 7.4° below Elnath.  As midnight approaches, the bright moon (18.8d, 83%) is less than 5° up in the east-southeast, 13.0° below Zubeneschamali (“the northern claw,” β Lib, m = 2.6).

Read more about the planets during March 2021.

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