2021, May 18: Planet Quintet, Waxing Moon

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May 18, 2021: Bright morning planets Jupiter and Saturn are in the southeast before sunrise.  After sunset, Evening Star Venus, Mercury, and Mars are lined up in the western sky.  The thick crescent moon is higher near Regulus.

Chart Caption – 2021, May 18: Bright morning planet Jupiter, in Aquarius, is above the southeastern horizon before sunrise. Saturn is 16.9° to the upper right of the Jovian Giant.

by Jeffrey L. Hunt

Chicago, Illinois:  Sunrise, 5:28 a.m. CDT; Sunset, 8:07 p.m. CDT.  Check local sources for sunrise and sunset times for your location.

Morning Sky

Bright morning planet Jupiter and Saturn are in the southeast before sunrise.  The gap between the planet duo continues to grow after their great conjunction on the day of the winter solstice.

One hour before sunrise, Jupiter – brighter than all the stars in the morning sky – is about 20° up in the southeastern sky.  It is slowly moving eastward compared to the dim stars of Aquarius.

Use a binocular to see Jupiter’s place compared to Iota Aquarii (ι Aqr on the chart) and Theta Aquarii (θ Aqr).  The Jovian Giant is 1.9° to the upper left of Iota and 4.6° to the lower right of Theta.

Saturn – brighter than nearly all the stars this morning except for Jupiter, Vega, and Arcturus – is 16.9° to the upper right of Jupiter.  The Ringed Wonder is 0.6° to the right of Theta Capricorni (θ Cap).

In less than a week, Saturn seems to reverse its eastward motion compared to Theta.  The planet appears to move westward and away from the star.  This backwards or retrograde motion is an illusion as our planet begins to pass between Saturn and the sun.

Jupiter and Saturn lead the sun and evening planets across the sky.  The two large planets set during the daytime.  The evening planets, Venus, Mercury, and Mars appear in the west after sunset.  They rise during the daytime and follow our central star across the sky.

Evening Sky

Chart Caption – 2021, May 18: Thirty minutes after sunset, brilliant Venus is low in the west-northwest. Mercury is 8.0° to the upper left of Venus.

After sunset, brilliant Evening Star Venus appears low in the west-northwest at 30 minutes after sunset when it is 6° above the horizon.  It passed on the far side of the sun, superior conjunction, on March 26.  It continues to make its slow appearance in the evening sky.

Mercury, after its greatest separation from the sun, is a little lower and slightly dimmer in the sky each night.  This evening, use a binocular to find this speedy planet 8.0° to the upper left of Venus.  It is just out of the same field of view that has Venus in it.  First find Venus then move the binocular slightly until Venus disappears at the lower right edge of the field of view.  Mercury will then appear in the upper left edge.

Venus as an evening star article.

Read more about Venus in our summary document.

Chart Caption – 2021, May 18: Forty-five minutes after sunset, Venus, Mercury, and Mars are in the western sky. The moon is outside this view.

By 45 minutes after sunset, Mercury is bright enough to be seen without the binocular’s optical assist, when it is nearly 9° above the horizon.  If the observing spot has a clear horizon to the west-northwest, Venus is still in the sky to the lower right of Mercury.

The star Elnath – “the one butting with horns” – is 4.2° to the upper right of Mercury.  This star is the northern horn of Taurus.

Mars, dimmer than Mercury, is 25° to the upper left of the speedy planet.  The thick crescent moon is 33° to the upper left of Mars, making Mars about halfway from Mercury to the moon.

Here’s more about Mercury during May 2021.

Chart Caption – 2021, May 18: An hour after sunset, Mars is about one-third of the way up in the west, 3.3° to the upper right of Zeta Geminorum (ζ Gem) and 3.5° to the lower right of Delta Geminorum (δ Gem).

An hour after sunset, Mars is about one-third of the way up in the west in front of Gemini’s starry backdrop.  The planet is marching eastward through the constellation.

The Red Planet is under Castor and Pollux.  In the dimmer starfield, it is 3.3° to the upper right of Mekbuda, “the folded paw of the lion,” (ζ Gem on the chart) and 3.5° to the lower right of Wasat (δ Gem), “the middle of the sky.”

Here’s more about Mars during 2021.

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

Chart Caption – 2021, May 18: The thick crescent moon is in the west-southwest, 11.4° to the lower right of Regulus.

The waxing crescent moon is higher in the sky in the west-southwest.  The lunar orb is 11.4° to the lower right of Regulus, “the prince.”

Regulus is the brightest star in Leo.  The westward facing Lion is tipping toward the western horizon.  The backwards question mark, that includes Regulus, is the head of the celestial big cat.  The small triangle to the east (left) of Regulus make the haunches and includes the tail, Denebola.

Regulus is the closest bright star to the ecliptic, less than one-half degree above the plane of the solar system.

Venus is closing the gap on Mars.  Venus passes the Red Planet on July 12.  This occurs when these planets are near Regulus, but the constellation is much lower in the sky.

Tonight, Venus sets 69 minutes after sunset and this grows about one minute each evening,  Mercury follows Venus to the horizon nearly 50 minutes later.  Mars sets nearly four hours after sunset, about 85 minutes before Saturn rises in the southeastern sky to open tomorrow’s planet exhibition.

Detailed Note: One hour before sunrise, Jupiter is over 23° up in the southeast.  Use a binocular to spot Jupiter with the stars, 1.9° to the upper left of ι Aqr and 4.6° to the lower right of θ Aqr.  Saturn is 16.9° to the upper right of bright Jupiter.  The Ringed Wonder is 0.6° to the right of θ Cap.  Saturn appears to be slowing down before it reverses its direction to retrograde. Three planets are visible after sunset.  Thirty minutes after sunset, brilliant Venus is over 6° above the west-northwest horizon.  Use a binocular to find Mercury (m = 0.6), 8.0° to the upper left of Venus.  The moon (7.3d, 42%) is nearly 60° up in the west-southwest. Fifteen minutes later, Venus is about 4° above the horizon, while Mercury is nearly 9° up. This speedy planet is a few days after its greatest elongation and sets 116 minutes after sunset. Mercury is 4.2° to the lower left of Elnath.  Mars is nearly one-third of the way up in the west, over 25° to the upper left of Mercury. The moon is 11.4° to the lower right of Regulus (α Leo, m = 1.3).  By one hour after sunset, Venus is just above the horizon and Mercury is about 9° in altitude.  Use a binocular to see the starfield with Mars.  The Red Planet is 3.3° to the upper right of ζ Gem and 3.5° to the lower right of δ Gem. 

Read more about the planets during May 2021.

Venus from Galileo (NASA photo)

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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