2021, August 16: Five Evening Planets, Moon

Astronomy, Sky Watching
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August 16, 2021:  Mercury and Mars are visible through a binocular during bright twilight.  As night falls, Venus, Saturn and Jupiter are visible.  The gibbous moon is near Antares.

Chart Caption – 2021, August 16: Through a binocular twenty minutes after sunset, Mercury is 2.2° to the lower right of Mars.

by Jeffrey L. Hunt

Chicago, Illinois:  Sunrise, 6:00 a.m. CDT; Sunset, 7:49 p.m. CDT.  Check local sources for sunrise and sunset times for your location.

This evening the five brightest planets are visible in the evening sky.  Two of them, Mercury and Mars, are a challenge to see during bright twilight, but they are in the same binocular field.  Brilliant Venus, Saturn, and Jupiter are easily seen, along with the bright moon.

With a binocular, start looking for Mercury about 25 minutes after sunset.  It is bright, but somewhat hiding in bright twilight.  Mars is in the same binocular field, 2.2° to the upper left of Mercury.

Mercury passes to about 0.1° of Mars in two evenings.  This is the closest conjunction of the two planets until 2032.  About 18 other conjunctions of the two planets occur during the interval, but none as close as the one this year.

Chart Caption – 2021, August 16: About 45 minutes after sunset, Venus is low in the west among the stars of Virgo.

Twenty minutes later (45 minutes after sundown), brilliant Venus is easily visible about 8° up in the west, shining through the colorful layers of evening twilight.  The planet is stepping eastward each evening toward Spica for a wide conjunction on September 5. Look each evening to watch Venus close in on Spica.

This evening the brilliant planet is 3.5° to the upper left of Zavijava, “the corner of the barking dog,” and 4.1° to the lower right of Zaniah, “the corner.”  Use a binocular to find the dimmer stars with the planet.  The trio does not fit into the same binocular at the same time.  The planet and one of the stars can be seen together with the optical assist of the binocular.

Porrima, also known as Gamma Virginis, is 9.6° to the upper left of Venus.

Chart Caption – 2021, August 16: The moon is to the upper left of Antares, “the rival of Mars.”

The bright waxing gibbous moon is over 20° up in the south. The lunar orb is over 65% illuminated this evening.  It is 4.4° to the upper left of Antares.

Antares is a very large star, summer’s complement to winter’s Betelgeuse.  It is about 600 light years away, shining with a brightness of over 20,000 suns.  It is very large and if it were empty, it would hold the solar system from the sun out to about Jupiter’s orbit.

According to astronomical theories, Antares is nearing the end of its life cycle.  When stars are at this stage they grow in size, brighten, and cool.  A star is not required to be blue hot to shine brightly.

The star’s name is translated as “the rival of Mars.”  The word is a combination of Ant and Ares.  Ares is the Greek god equivalent to Mars, as the translation indicates.  The prefix “Ant” is defined as “against.”  Perhaps we can extend this to “not.”  Maybe the name means “Not Mars.”  When I see the star in the sky, I think, “This star is not Mars.” 

Antares is somewhat near the plane of the solar system, where the planets track around the sun from our perspective in the sun’s family.  It is over 4° to the south of the ecliptic.

Mars is about the same color as Antares, although the planet’s hue is from sunlight reflected from its surface.  Depending on Earth’s distance from Mars when we see the Red Planet near the star, both can be about the same brightness.

Mars passes 4.5° to the upper left of Antares on December 27, in the southeastern sky before sunrise.  During the few days when Mars is near the star, Antares is about 60% brighter than the planet.

Chart Caption – 2021, August 16: Forty-five minutes after sunset, Saturn and Jupiter are low in the southeastern sky.

Saturn and Jupiter are farther eastward at this hour.  The Ringed Wonder is nearly 14° up in the southeastern sky.  Bright Jupiter is to Saturn’s lower left and near the horizon.  If the neighbor’s house or neighborhood trees block your view toward than direction, wait until later in the evening to see the two giant planets, higher in the southeast.

Both of the planets are retrograding.  Earth was between the Sun and Saturn earlier this month.  Jupiter’s opposition occurs in three evenings.

Retrograde motion is an illusion when our faster moving planet moves between the outer planets and the sun.

Detailed Daily Note:One hour before sunrise, Jupiter – retrograding in Aquarius – is over 14° up in the west-southwest.  It is 1.5° to the lower right of ι Aqr, 1.6° to the upper left of μ Cap, and 4.1° above Deneb Algedi.  Twenty-five minutes after sunset, attempt to spot Mercury, about 3° up in the west.  It is 2.2° to the lower right of Mars.  In two evenings, the Mercury – Mars conjunction occurs.  The impending planetary meeting is the 21st closest in a set of close conjunctions from 2013 through 2039.  While occurring during bright twilight, attempt to view it.  Forty-five minutes after sunset, Venus is about 8° up in the west.  Use a binocular to spot it 3.5° to the upper left of Zavijava and 4.1° to the lower right of Zaniah (η Vir, m = 3.9).  Venus is speeding toward Spica, over 14° above the west-southwest horizon.  The gap is 23.2° this evening.  Farther eastward along the ecliptic, the moon (8.5d, 66%) is about 24° up in the south, 4.4° to the upper left of Antares.  Saturn is nearly 14° above the southeast horizon.  Bright Jupiter is to the Ring Wonder’s lower left, about 6.5° up in the east-southeast.  By two hours after sunset, the bright moon and Antares are in the south-southwest.  Saturn is nearly 23° up in the south-southeast, 1.5° to the lower left of υ Cap.  At this hour, Jupiter is 18.0° above the southeastern horizon.

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One comment

  1. Good morning what a lucky day as with my camera got 19 great photos of the planet alignment. will post to fb later today. what a site to see. thank you brian walls

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