2021, May 3: Evening Star Venus, Mercury, Mars

May 3, 2021: Three bright planets are visible after sunset. Brilliant Venus is low in the west-northwest, with Mercury to its upper left.  As the sky darkens further a binocular reveals that speedy Mercury is to the lower left of the Pleiades star cluster.  Mars is visible in a darker sky in Gemini, below Castor and Pollux.

by Jeffrey L. Hunt

Chicago, Illinois:  Sunrise, 5:44 a.m. CDT; Sunset, 7:52 p.m. CDT.  Check local sources for sunrise and sunset times for your location.

Five planets are visible during a 24-hour period.  This evening, Venus and Mercury are visible soon after sunset.  Mars is visible when the sky is darker in the western sky.  Jupiter and Saturn are morning planets that are visible in the southeast before sunrise.

Twenty minutes after sunset Venus is nearly 5° above the west-northwest horizon.  Use a binocular to initially locate it.  Mercury is 6.4° to the upper left of Venus.  It is bright, but likely outside the binocular field that includes Venus.

Read more about Venus in our summary document.

About 45 minutes after sunset, Mercury is nearly 7° above the west-northwest horizon.  Use a binocular to see the Pleiades star cluster to the upper right of the speedy planet.  This evening, the cluster’s brightest star, Alcyone (η Tau on the chart), is 2.1° to the upper right of Mercury.

Here’s more about Mercury during May 2021.

This might be the last evening to see Rigel, “Orion’s left knee,” before it disappears into bright sunlight.  This is known as the star’s heliacal setting.  It reappears in the eastern sky before sunrise later in the summer.

Sirius, Aldebaran, and Betelgeuse disappear into the sun’s brightness this month.

Look for Rigel very low near the west-southwest horizon about 40 minutes after sunset.

An hour after sunset, Mars, over 36° up in the west, is in front of the stars of Gemini, below Castor and Pollux.  It is 2.4° to the upper right of Tejat Posterior, “the heel,” (μ Gem on the chart) and 3.0° to the lower right of Mebsuta, “the outstretched paw of the lion,” (ε Gem).

Here’s more about Mars during 2021.

Detailed Note: One hour before sunrise, the moon (21.3d, 54%) is over 18° above the south-southeast horizon. The lunar slice is 6.8° to the lower right of Saturn.  Bright Jupiter is 15.5° to the lower left of Saturn.  In the starfield, Saturn is 0.9° to the right of θ Cap, while Jupiter is 1.3° above ι Aqr.  The moon is at its Last Quarter phase at 2:50 p.m. CDT.  Twenty minutes after sunset, Venus is nearly 5° above the west-northwest horizon.  Have you observed it without a binocular?  Mercury (m = −0.9) is 6.4° to the upper left of Venus. This might be the last evening to see Rigel, “Orion’s left knee,” (β Ori, m = 0.2), without optical assistance near the horizon about 40 minutes after sunset. Forty-five minutes after sunset, Mercury is nearly 7° up in the west-northwest, 2.1° to the lower left of η Tau. Fifteen minutes later, Mercury is only 4° above the horizon.  Mars is over 36° to the upper left of Mercury and below the Gemini Twins, Castor and Pollux.  In the starfield, Mars is 2.4° to the upper right of μ Gem and 3.0° to the lower right of ε Gem.

Read more about the planets during May 2021.