2021, April 25: Mercury-Venus Conjunction, Mars, Bright Moon


April 25, 2021: Mercury passes Evening Star Venus this evening after sunset.  Look low in the western sky about 20 minutes after sunset.  Mars is marching eastward in Gemini, near the star cluster Messier 35.  The bright moon is near Spica.

by Jeffrey L. Hunt

Chicago, Illinois:  Sunrise, 5:55 a.m. CDT; Sunset, 7:43 p.m. CDT.  Check local sources for sunrise and sunset times for your location.

Chart Caption – 2021, April 25: Brilliant Venus and Mercury are low in the west-northwest after sunset.

Three planets are visible in the evening sky along with the nearly full moon.  Brilliant Venus is entering the sky from bright twilight. 

Mercury is beginning its best evening appearance of the year.  The speedy planet passes Venus this evening for the first of two conjunctions during the next several weeks.

Twenty minutes after sunset use a binocular to find Venus about 3° up in the west-northwest. Mercury is 1.2° to the upper right of the planet. 

Mercury is brighter than the brightest star Sirius, but the planet fades in brightness throughout its appearance.  By the next conjunction during late May, the planet is considerably dimmer.

This evening, both planets are likely visible to the unaided eye, but the window to see them is quite small with or without a binocular’s assistance.  Venus sets 38 minutes after sunset, and Mercury sets only four minutes later.

Read more about Venus in our summary document.

Chart Caption – 2021, April 25: One hour after sunset, Mars is at the feet of Gemini, Castor and Pollux.

One hour after sunset, Mars is less than halfway up in the west at the feet of Gemini.  It is 3.1° to the lower right of Propus, “the projecting foot” (η Gem on the chart). 

Chart caption – 2021, April 25: In this binocular view, Mars is near the star cluster Messier 35 and Propus (η Gem).

The Red Planet is marching eastward in Gemini.  This evening it is 0.8° to the lower right of a star cluster known as Messier 35 (M35 on the chart).  With the bright moon in the southeast, finding the cluster with a binocular is a challenge.

Stars are theorized to form in bunches.  Some of the clusters are relatively nearby in the galactic neighborhood and easily seen with the unaided eye, such as the Pleiades star cluster and the Hyades star cluster in Taurus.  Others are farther away and appear as cloudy blotches of light to the unaided eye.  A binocular reveals individual stars.

Tomorrow evening, Mars is closest to the cluster, but the moon continues to fill the sky with bright light.

Mars sets in the west-northwest over 4 hours after sunset.

Here’s more about Mars during 2021.

Read about Mars during April.

Chart Caption – 2021, April 25: The bright moon is in the southeast, 6.1° to the upper left of Spica.

That bright moon, 98% illuminated, is 6.1° to the upper left of Spica, “the ear of corn,“ the brightest star in Virgo.

The constellation Corvus, the Crow, is to the lower right to the moon.

Block the moon’s glare, as you would to shield your eyes from the sun, to see the star and the tiny constellation near the moon this evening.

Detailed Note: One hour before sunrise, Jupiter is 15.0° above the east-southeast horizon. It is now in Aquarius. Among the stars, it is 4.1° to the upper left of Deneb Algiedi, 1.4° to the lower left of μ Cap, and 2.0° to the upper right of ι Aqr.  Saturn is 14.6° to the upper right of brighter Jupiter.  It is slowly approaching θ Cap.  This morning the gap is 1.2°. Twenty minutes after sunset, Venus is over 3° up in the west-northwest.  Mercury (m = −1.6) passes 1.2° to the upper right of the brilliant planet. Both planets might be visible to the unaided eye.  As the sky darkens further, Mars is less than 40° in altitude above the west horizon.  It is 1.6° to the upper right of 1 Gem and 3.1° to the lower right of Propus.  In this bright moonlight, use a binocular to spot the star cluster M35, 0.8° to the upper left of Mars. The moon (14.0d, 98%) – less than one-third of the way up in the sky above the east-southeast horizon – is 6.1° to the upper left of Spica.

Read more about the planets during April 2021.


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