2021, August 18: Challenging View, Five Planets, Moon

Astronomy, Sky Watching
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August 18, 2021: During bright twilight, five planets and the moon are in the sky simultaneously after sunset.  This is a challenging observation made with the assistance of a binocular or spotting scope.  Mercury and Mars are at their closest in the west, with brilliant Venus to the upper left.  The moon, Saturn, and Jupiter are in the southeastern sky. The Mercury – Mars conjunction is the closest until 2032.

Chart Caption – 2021, August 18: Venus, Mercury, Mars are in the western sky.

by Jeffrey L. Hunt

This evening there is a challenging observation of the five bright planets – Mercury, Venus, Mars, Jupiter, and Saturn – during bright twilight. The gibbous moon participates in this planet parade as well.

In many descriptions of events on these pages, observations of events are described as “stretches.”  This evening’s sighting of half a dozen planetary objects is beyond that in difficulty to see.  It’s exceeding our limits for viewing typical events.

Chart Caption – 2021, August 18: Mars is 0.1° to the upper left of Mercury. This is the closest conjunction of the two planets until 2032.

This evening, Mercury passes 0.1° to the lower right Mars! 

This evening’s conjunction ranks 25th closest on a list of 30 spanning 2013 – 2039, compiled by Jean Meeus.  Mercury passes closer to Mars on August 23, 2032, the third closest – according to Meeus.

The 2032 conjunction is much less than 0.1° apart. By the time the conjunction is visible in the Americas, Mercury has moved 0.3° away from the Red Planet.  Before the 2032 event, 18 other Mercury – Mars conjunctions occur; one-third of them are too close to the sun to be seen with conventional observing techniques.

This evening’s event has a very short window and you’ll need clear horizons to see the planets simultaneously.

Here’s what to look for:

At 25 minutes after sunset, bright Mercury and Mars are 3° up in the west, 7° north of the west cardinal direction.  Mercury is bright, but not quite naked eye at this time.  Search for it with a binocular.  Mars is 0.1° to the upper left of the speedy planet.

Brilliant Venus is in the sky, but not close enough to Mercury to easily use it as a guide.  Earth’s Twin planet is over 20° to the upper left of Mercury.  Venus is over 11° up in the west-southwest.

Chart Caption – 2021, August 18: Jupiter, Saturn, and the gibbous moon are in the eastern sky.

The moon, Saturn, and Jupiter are in the eastern sky.  The moon – 86% illuminated- is easy to locate, since it appeared in the sky nearly three hours ago.

Bright Jupiter is over 3° up in the east-southeast.  Use a binocular.

Saturn’s sighting is a little more challenging. It is less than halfway from Jupiter to the moon.

Estimate the distance and point your binocular in the region.  Use a grid pattern (move the binocular up and down and then to the left or right slightly and repeat) to find the Ringed Wonder.

If you found them congratulations!

Tomorrow evening, the planets are nearly in the same spot.  Mars is 0.9° to the lower right of Mercury.  Each evening Mars becomes more of a challenge – near impossibility to see at this time as it moves toward its solar conjunction.  The moon is 4.6° below the Ringed Wonder, making the attempt to find Saturn easier.  In many binoculars, the moon and Saturn fit into the same field of view.

The next attempt to see five planets simultaneously occurs during June 2022, when the five bright planets are in the morning sky.

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