During May 2021, Mars marches across the starfields of Gemini. The planet is visible in the western sky after sunset. Early in the month, Mars is near the feet of Castor. Mars moves through the constellation diagonally from lower right to upper left. It ends the month passing Pollux.
By Jeffrey L. Hunt
After its close opposition to Earth during October 2020, Mars has been slowly moving eastward through the constellations. As Earth, moving faster on an inner orbit, moves away from Mars, the Red Planet continues to dim in our sky, yet it is brighter than most of the stars in the western sky.
Mars is slowly moving toward the sun from our view. The Red Planet is at its solar conjunction on October 7.
Meanwhile the planet starts the evening over one-third of the way up in the west below Castor and Pollux. The stellar pair is of nearly equal brightness and relatively close together. Mars is brighter than the Twins and lower in the sky.
Each night the planet is in a different place in the starfield. A binocular is not necessary, but it helps to locate the dimmer stellar background.
On the evening of May 15, the crescent moon is near Mars.
In the notes that follow, look for the planet in the western sky an hour after sunset.
- May 2: Nearly 35° up in the west, Mars passes 2.2° to the upper right of Tejat Posterior, “the heel,” (μ Gem on the chart above).
- May 9: Over one-third of the way up in the west, Mars passes 0.6° to the lower left of Mebsuta (ε Gem, m = 3.0).
- May 15: Less than 30° in altitude in the west, Mars is 2.2° to the upper left of the moon (4.3 days after the New moon phase, 16% illuminated).
- May 16: Nearly 29° up in the west, Mars is to right of a line from Castor to Alhena, “the brand-mark,” (γ Gem). The planet is 10.6° to the lower left of Castor and 9.5° to the upper right of Alhena.
- May 17: (1.7, 4.4”, 2.15AU, 226m) About 28° up in the west, Mars is to the left of a line that extends from Castor and Alhena. Mars is 10.3° to the lower left of Castor and 9.8° to the upper right of Alhena.
- May 22: Nearly 26° in altitude in the western sky, Mars is between Pollux and Alhena. Mars is 7.5° below Pollux and 11.8° above Alhena.
- May 23: About 25° up in the west, Mars passes 1.5° to the upper right of Wasat, “the middle of the sky,” (δ Gem).
- May 24: Mars is about 25° up in the west. It passes 4.3° below Iota Geminorum (ι Gem).
- May 28: Mars – less than 25° altitude in the west – passes 3.8° to the lower left of Upsilon Geminorum (υ Gem).
- May 31: Over 20° up in the west-northwest, Mars passes 5.3° to the lower left of Pollux.
Read more about the planets during May 2021.
Here’s more about Mars during 2021.
May 13, 2021: Venus, Mercury, the crescent moon, and Mars are in the western sky after sunset.
May 13, 2021: Bright Jupiter and Saturn are the morning planets in the southeast before sunrise.
May 12, 2021: Thirty minutes after sunset, the razor-thin moon is 1.2° to the left of brilliant Venus. This is the closest grouping of the moon and Venus during this evening appearance of the brilliant planet. Mercury is 9.1° to the upper left of Venus. Mars maintains its eastward march in Gemini. Sirius and Aldebaran are near their heliacal settings, their final appearances in the evening sky for the year.
May 12, 2021: Before sunrise bright Jupiter, in front of Aquarius, is in the southeast before sunrise. Saturn is to the upper right of Jupiter, in Capricornus. In a few mornings, Saturn begins to retrograde.
May 11, 2021: The planet parade continues today. Five planets are on display. Bright Jupiter and Saturn are in the southeastern sky before sunrise. After sundown, brilliant Venus, Mercury, and Mars are in the western sky. The moon is at its New phase and at apogee today.