2021, May 17: Planets, Moon Line Up

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May 17, 2021: The five bright planets – Saturn, Jupiter, Venus, Mercury, and Mars – are visible in night sky.  Jupiter and Saturn are in the morning.  Evening Star Venus, Mercury and Mars are in the evening sky with the crescent moon.

Chart Caption – 2021, May 17: Morning planets, Jupiter and Saturn, are in the southeast before sunrise.

by Jeffrey L. Hunt

Chicago, Illinois:  Sunrise, 5:28 a.m. CDT; Sunset, 8:06 p.m. CDT.  Check local sources for sunrise and sunset times for your location.

The planet parade continues tonight.  The five planets are visible either before sunrise or after sunset.  Mercury is one evening past its greatest separation from the sun.  It is beginning to move back into the bright sunlight.  It dims considerably during the next week leading up to its close conjunction with Venus.  Look for Jupiter and Saturn before sunrise and Venus, Mercury, and the crescent moon after sunset.

Morning Sky

Morning planets, Jupiter and Saturn are in the southeastern sky before sunrise.  Saturn, brighter than most of the stars in the sky this morning, is less than one-third of the way up in the south-southeast at one hour before sunrise.

In less than a week, Saturn begins to retrograde, appear to move westward compared to the stars.

The planet has been near the star Theta Capricorni (θ Cap on the chart).  Use a binocular to spot the star 0.6° to the left of Saturn.

Jupiter, over 20° above the southeast horizon, is nearly 17° to the lower left of Saturn.  Jupiter is slowly moving eastward in Aquarius.

Use a binocular to make observations each clear morning of Jupiter’s place compared to Iota Aquarii (ι Aqr) and Theta Aquarii (θ Aqr).  The Jovian Giant is 1.8° to the upper left of Iota and 4.7° to the lower right of Theta.

The planet parade is interrupted by the sun.  Saturn and Jupiter set in the western sky during the daytime.  Venus, Mercury, Mars, and moon rise after the sun and follow the blazing sphere across the sky.  The final three and the lunar slice become visible in the western sky above where the sun disappeared below the horizon.

Evening Sky

Chart Caption – 2021, May 17: Thirty minutes after sunset, use a binocular to initially locate Venus. Mercury is 8.4° to the upper left of Venus.

Mercury reached its greatest elongation after midnight earlier today.  The planet begins its plunge back into bright sunlight.  This takes until the end of the month.  Each evening it dims, and it is closer to Venus.

Venus is over 6° above the west-northwest horizon.  Mercury is 8.4° to the upper left of Venus.

Use a binocular to see it.  The gap between the planets is too large for both of them to fit in the field of view of most binoculars.  First, find Venus. Then move the binocular so that the brilliant planet is at the lower right portion of the binocular field.  Finally, move the binocular to the upper left so that Venus seems to move from the field.  Mercury enters the field of view at the upper left.

Venus as an evening star article.

Read more about Venus in our summary document.

Chart Caption – 2021, May 17: Forty-five minutes after sunset, brilliant Venus, Mercury, Mars, and the crescent moon line up in the western sky.

By 45 minutes after sunset, Mercury is visible to the unaided eye over 10° above the horizon.  If the horizon is unobstructed, Venus is still there, about 4° up in the sky.

The crescent moon – over 30% illuminated – is over halfway up in the western sky.  As the sky darkens, Pollux is visible, 13° to the lower right of the lunar slice.

Mars, dimmer than Mercury, is over 25° to the upper left of that speedy planet.

The Northern Horn of Taurus, Elnath – “the one butting with horns” – is 4.7° to the upper right of Mercury.

Here’s more about Mercury during May 2021.

Chart Caption – 2021, May 17: Mars is marching eastward in Gemini below Castor and Pollux. The crescent moon is to the upper left of Pollux.

An hour after sunset, Mars is in Gemini, under Castor and Pollux.  The planet is marching eastward through the constellation. In the starfield, it is 4.8° to the upper left of Mebsuta (ε Gem on the chart, 3.3° to the upper right of Mekbuda (ζ Gem), and 4.1° to the lower right of Wasat (δ Gem).

Here’s more about Mars during 2021.

Find a detailed chart of the motion of Mars during the month here.

Detailed Note: Mercury reaches its greatest elongation (22.0°) at 12:54 a.m. CDT. The five naked-eye planets are visible today, two in the morning sky, three, evening.  One hour before sunrise, Saturn is nearly 26° up in the south-southeast, 0.6° to the right of θ Cap.  The planet is nearing when it reverses its eastward motion compared to the stars and begins to retrograde.  Bright Jupiter, over 22° above the southeast horizon, is 16.8° to the lower left of Saturn.  In the starfield, Jupiter is 1.8° to the upper left of ι Aqr and 4.7° to the lower right of θ Aqr.  Begin looking for the evening planets 30 minutes after sunset.  At this time, brilliant Venus is over 6° above the west-northwest horizon.  In this bright twilight, use a binocular to locate Mercury (m = 0.4), 8.4° to the upper left of Venus. The moon (6.3d, 32%) is 50.0° up in the west-southwest.  Fifteen minutes later, find Pollux, 13.0° to the lower right of the crescent moon. Venus is lower in the west-northwest, about 4° above the horizon.  Mercury is 4.7° to the lower left of Elnath.  Mars, in the middle of Gemini, is nearly 26° to the upper left of Mercury.  By one hour after sunset, Venus is just above the horizon, while Mercury is nearly 9° up.  Use a binocular to see Mars against the distant starfield.  The Red Planet is 4.8° to the upper left of ε Gem, 3.3° to the upper right of ζ Gem, and 4.1° to the lower right of δ Gem.  The setting time intervals after sunset: Venus, 69 minutes; Mercury, 117m; Mars, 226m; moon, over 5 hours.

Read more about the planets during May 2021.

2021 – 2022, Venus – Mars Triple Conjunction

During 2021 into 2022, Venus passes Mars three times for a triple conjunction.  The first occurs on July 12, 2021.  The others occur during early 2022, followed by a close approach of the two planets.

2021, July 6: Venus – Saturn Opposition

July 6, 2021:  This is the second bright planet – planet opposition this month.  Venus and Saturn are in opposite directions from Earth.  Venus sets about the time that Saturn rises.  After this date, Venus and Saturn together are in the evening sky until early 2022.

2021, June 26 – June 30: Bright Moon, Morning Planets

June 26 – June 30, 2021:  The bright gibbous moon passes Jupiter and Saturn in the morning sky before sunrise.  Observe that the moon is in a different spot each morning, farther east toward the impending sunrise.

2021, June 15: Moon, Sickle of Leo

June 15, 2021:  The moon is with the Sickle of Leo this evening.  Step outside about an hour after sunset to find the crescent moon that is about 30% illuminated over one-third of the way up in the west.



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