2021, August 27: Morning Moon, Evening Inner Planets

August 27, 2021:  The bright moon is near Aries in the morning sky.  Look for Venus and Mercury shortly after sunset.

2021, August 27: Before sunrise, the gibbous moon is to the lower right of the brightest stars in Aries.
Chart Caption – 2021, August 27: Before sunrise, the gibbous moon is to the lower right of the brightest stars in Aries.

by Jeffrey L. Hunt

Chicago, Illinois:  Sunrise, 6:12 a.m. CDT; Sunset, 7:32 p.m. CDT.  Check local sources for sunrise and sunset times for your location.

Before sunrise, the bright gibbous moon is high in the south-southwestern sky.  It is among the stars of Pisces, to the lower right of the trio of stars that make Aries.  They are Hamal, Sheratan, and Mesartim. The stellar triad easily fits into the same binocular field of view.

The brightest star is Hamal – “the full-grown lamb.”  The star is nearly 10° north of the ecliptic, the plane of the solar system.  Its distance is about 70 light years, shining with a brightness of about 100 suns.

The star appears to have a planet revolving around it.  Known as Alpha Arietis b, the world is thought to be a gas planet like Jupiter, although the exoplanet has 1.8 times more matter and a diameter that is 1.2 times larger than our solar system’s largest planet.  It revolves around the star in a little over one Earth-year.

As of this writing Alpha Arietis b is one of more than 4,400 known exoplanets listed on NASA’s web site.

Hamal is a yellow-orange star, similar to that of brighter Aldebaran, visible to the lower left of the Pleiades star cluster this morning. Hamal’s color is easier to see in a binocular than to the unaided eye.

Sheratan – “the two signs” – is nearly 4° to the lower right of Hamal. The star is around 60 light years away.  It is about 50 times brighter than our sun.  Its color is different from Hamal.  Sheratan is a blue-white star.

The third star in the triangle is Mesartim – “the extremely fat ram.”  It is the farthest and hottest star of this triad, about 200 light years away.   It is over 100 times brighter than our sun.

Mesartim is a double star that was first observed through a telescope during the 17th century.

The moon is approaching the Pleiades and the constellation Taurus.  Notice the change during the next few mornings.

2021, August 27: After sunset, Mercury is over 17° to the lower right of Evening Star Venus.
Chart Caption – 2021, August 27: After sunset, Mercury is over 17° to the lower right of Evening Star Venus.

This evening brilliant Venus shines from the western sky after sunset.  Mercury is heading toward a greatest elongation from the sun next month, but this appearance of the speedy planet is dismal.  It is over 17° to the lower right of the brilliant Evening Star.

About 25 minutes after sunset, Mercury is about 4° up in the west.  At this level of twilight, a binocular is needed to see it.

As the sky darkens further, Venus, and Jupiter and Saturn – in the southeast – are visible at the same time.  This trio of bright planets is visible at the same time during the evening until early 2022.

Detailed Daily Note:One hour before sunrise, the moon (18.8d, 76%) is nearly two-thirds of the way up in the sky above the south-southwest horizon. The lunar orb is 14.1° to the lower right of Hamal.  Farther west, Jupiter is 4.0° up in the west-southwest.  Twenty-five minutes after sunset, Mercury (m = −0.1), over 4° up in the west, is 17.1° to the lower right of Venus.  Use a binocular to see them. Mercury’s brightness continues to dim as it reaches out to its greatest evening elongation next month. Forty-five minutes after sunset, brilliant Venus is about 8° up in the west-southwest, 4.4° to the lower left of Porrima and 10.3° to the lower right of Spica. The planet continues to move eastward about 1.2° of ecliptic longitude from evening to evening.  Farther eastward, Saturn, over 17° up in the southeast, is 17.8° to the upper right of Jupiter.  The Jovian Giant is nearly 11° above the east-southeast horizon.  As midnight approaches, the moon (19.6d, 69%) is 15.0° above the eastern horizon and 18.8° to the upper right of Alcyone, the brightest star in the Pleiades star cluster.  Farther westward, Jupiter, over one third of the way up in the south and east of the meridian, is 2.9° to the upper right of ι Aqr, 0.5° to the lower left of μ Cap and 2.7° to the upper left of Deneb Algedi.  Saturn, less than one-third of the way up in the south and west of the meridian, is 1.1° to the lower left of υ Cap.  Both giant planets continue to retrograde in front of the stars of Capricornus.

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