2021, May 31: Goodbye, Mercury!

Astronomy, Sky Watching
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May 31, 2021: The planet parade is cut to four bright participants as Mercury departs the evening sky after tonight’s final appearance.  “Goodbye, Mercury!” until it appears in the morning sky during early summer.  This morning the moon is near Saturn and Jupiter in the southeastern sky. Brilliant Evening Star Venus, dim Mercury, and Mars are in the evening sky.

2021, May 31: The gibbous moon is to the lower left of Saturn during morning twilight.
Chart Caption – 2021, May 31: The gibbous moon is to the lower left of Saturn during morning twilight.

by Jeffrey L. Hunt

Chicago, Illinois:  Sunrise, 5:19 a.m. CDT; Sunset, 8:19 p.m. CDT.  Check local sources for sunrise and sunset times for your location.

At this latitude, daylight’s length is 15 hours.

Morning Sky

One hour before sunrise, the bright, gibbous moon is in the south-southeast before sunrise.  It is 6° to the lower left of Saturn.

The Ringed Wonder rises nearly five hours before sunup, followed by Jupiter less than an hour later.

This morning bright Jupiter is 18.1° to the east of Saturn.  Starlike Jupiter is brighter than all the stars this morning.  Only the Jovian Giant, Arcturus, and Vega are brighter than Saturn.

As the sun’s appearance interrupts the planet parade, the morning trio moves westward and sets during the day.

Evening Sky

Chart Caption – 2021, May 31: Forty-five minutes after sunset, three planets are in the evening sky.

After sunset, brilliant Venus shines from low in the sky, above where the sun set.

Chart Caption – 2021, May 31: Through a binocular, Mercury is 3.8° to the lower right of brilliant Venus.

Mercury is 3.8° to the lower right of Venus.  A binocular is needed to locate the elusive planet.

Speedy Mercury travels around the sun in 88 days.  From our view, the planet dances from morning sky to evening sky and back to the pre-sunrise sky.

During spring evening and autumn mornings, the plane of the solar system is oriented so that Mercury is visible higher in a darker sky.  From the mid-northern latitudes, it is rarely visible in a dark sky.  It sets before the end of evening twilight or rises before the opening of morning twilight.

During most apparitions, the planet sets during bright twilight.  Because the longer length of morning twilight, when Mercury waltzes into the morning sky, it rises 84 minutes before sunrise on July 9.  The planet is 5.5° up in the east-northeast at 45 minutes before sunrise.  Because morning twilight lasts, 128 minutes on this date, the planet is visible during bright twilight.

So, after its best evening appearance of the year and until it appears in the morning sky, we say, “Goodbye, Mercury!”

After this evening, the planet parade is reduced to four bright planets.

Chart Caption – 2021, May 31: Through a binocular, Mars is to the lower left of Pollux and Kappa Geminorum (κ Gem).

Mars is marching eastward in Gemini, 25.4° to the upper left of Venus.  While it is visible to the unaided eye, use the binocular notice that the Red Planet is 5.3° to the lower left of Pollux and 1.7° to the lower left of Kappa Geminorum (κ Gem on the chart).

Tomorrow evening Mars, Kappa Geminorum, and Pollux are in a line.  This evening Mars is below a line that starts at Pollux and extends through Kappa.

Venus moves eastward faster than Mars. During June, Venus cuts the separation down to about 7°.  During May, Venus cut 19° off the distance to Mars.

Mercury sets 62 minutes after sunset, followed by Venus about 20 minutes later.  Mars sets over 3 hours after sundown.

Articles and Summaries.

Detailed One hour before sunrise, the moon (19.6d, 70%) is nearly 25° up in the south-southeast, 6.0° to the lower left of Saturn.  In the starfield, use a binocular to see the Ringed Wonder, 0.6° to the right of the star θ Cap.  Saturn is slowly retrograding in Capricornus. Jupiter is 18.1° of ecliptic longitude east of Saturn.  The planet is brighter than all the stars in this pre-sunrise morning sky.  The Jovian Giant is over 15° to the upper left of the gibbous moon.  In the starfield, Jupiter is 2.4° to the upper left of ι Aqr, 4.1° to the lower left of θ Aqr, and 4.1° to the upper right of σ Aqr.  The month ends with 15 hours of daylight. Sunlit hours increase only several minutes until the solstice in 20 days. After sunset, Mercury (m = 3.0) is difficult to see.  After its best evening appearance and close conjunction with Venus, the speedy planet is racing toward inferior conjunction and difficult-to-see appearance in the morning sky during late spring and early autumn.  To find it first locate brilliant Venus, over 8° up in the west-northwest about 30 minutes after sunset.  Mercury is 3.8° to the lower right of Venus.  They are visible within a binocular’s single field of view.  We say “goodbye” to Mercury for this evening appearance.  Fifteen minutes later, Venus is 6.0° up in the sky and 6.9° to the upper left of Elnath. Mars, 25.4° of ecliptic longitude east of Venus, is nearly 25° up in the west among the stars of Gemini. During May, Venus has cut the gap to Mars by nearly 19°.  One hour after sunset, Venus is less than 4° above the horizon. Mars is 5.0° to the upper left of δ Gem, 1.7° to the lower left of κ Gem, and 5.3° to the lower left of Pollux.

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