2021, August 31: Morning Moon, Evening Planet Spectacular

August 31, 2021:  The morning moon is caught between the Bull’s Horns.  During the evening three bright planets – Venus, Jupiter, and Saturn – sparkle in the sky.

2021, August 31: The moon is caught between the Bull’s horns – Elnath and Zeta Tauri.
Chart Caption 2021, August 31: The moon is caught between the Bull’s horns – Elnath and Zeta Tauri.

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by Jeffrey L. Hunt

Chicago, Illinois:  Sunrise, 6:16 a.m. CDT; Sunset, 7:25 p.m. CDT.  Check local sources for sunrise and sunset times for your location.

Morning Sky

An hour before sunup the thick waning crescent moon is over halfway up in the east-southeastern sky.  The moon seems to be caught between the Bull’s horns, Elnath and Zeta Tauri.  This is the second time this month the moon has been between the horns.

The horn stars are too far apart to capture the moon in the same field of view with both of them.  The lunar orb fits into the field with one star at a time.

A fascinating “deep sky object” is in the direction of the moon and Zeta Tauri this morning.  This is the Crab Nebula, visible through a small telescope. Through an eyepiece, the nebula is a mere smudge of light.  Through a large telescope the Crab is a tangle of filaments and expanding gasses, resembling a crab.  At the center is a rotating neutron star with a strong magnetic field.  Its rapid rotation sends out pulses of radio waves and visible light – a pulsar.

This view of the Crab Nebula in visible light comes from the Hubble Space Telescope and spans 12 light-years. The supernova remnant, located 6,500 light-years away in the constellation Taurus, is among the best-studied objects in the sky. Credits: NASA/ESA/ASU/J. Hester
Photo Caption: This view of the Crab Nebula in visible light comes from the Hubble Space Telescope and spans 12 light-years. The supernova remnant, located 6,500 light-years away in the constellation Taurus, is among the best-studied objects in the sky. Credits: NASA/ESA/ASU/J. Hester

The nebula is the left-overs of an exploded star that was visible in 1054 and for nearly two years afterward. It was the brightest star in the sky and the crescent moon was nearby on July 4, 1054.  The brilliant exploding star that was recorded by Chinese, Japanese, and Islamic astronomers.  Native American sky watchers may have painted or carved the brilliant star and a crescent moon on walls and over hangs in the American Southwest.  While it makes a colorful explanation, this idea has been disputed by Griffith Observatory’s Ed Krupp.  The association with the supernova is likely a fanciful story.

With the moon in the vicinity this morning, the nebula is somewhat overwhelmed by the lunar reflection.  Note the place of the nebula compared to Zeta Tauri and the moon this morning and stop back with a telescope when the moon is a much thinner crescent or when it moves to the evening sky.  The nebula is in the sky each morning and then moves into the evening sky in a few months.  If you’re a fair-weather sky watcher with a telescope, the next few months are your opportunity to see the Crab Nebula before it moves into the cold season’s sky.

Evening Sky

 Four bright planets – Venus, Saturn, and Jupiter – are easily visible at about an hour after sunset.

2021, August 31: Difficult-to-see Mercury is low in the western sky at 25 minutes after sunset.
Chart Caption – 2021, August 31: Difficult-to-see Mercury is low in the western sky at 25 minutes after sunset.

The evening begins with a challenging view of Mercury.  It is making a poorly-visible apparition in the western sky.  About 25 minutes after sunset, the speedy planet is about 4° up in the west, 16.0° to the lower right of Venus.  Find a clear horizon and use a binocular.

2021, August 31: Forty-five minutes after sunset, Venus is low in the southwest – 5.8° to the right of Spica.
Chart Caption – 2021, August 31: Forty-five minutes after sunset, Venus is low in the southwest – 5.8° to the right of Spica.

At about 45 minutes after sundown, when the sky is darker, Evening Star Venus – 5.8° to the right of Spica – is about 8° above the west-southwest horizon.  On September 5, Venus passes above the star.

Venus appears to be struggling to climb higher in the sky each evening as it is farther southward.  After mid-September, Venus begins setting after the end of evening twilight and it begins a higher climb into the western evening sky.

At this hour, Saturn is over 18° above the southeast horizon.  Bright Jupiter is 17.6° to the lower left of the Ringed Wonder.

Each evening, Saturn and Jupiter are closer to Venus.  The gap continues to close through the end of the year, but there are no conjunctions of this planet pair with it in the evening sky.  This evening Saturn is 110° east of Venus.  During early July, Saturn was first visible with Venus, when they were about 180° apart.

Venus sets 89 minutes after sundown.

2021, August 31: Two hours after sunset, bright Jupiter and Saturn are set against the stars of Capricornus.
Chart Caption – 2021, August 31: Two hours after sunset, bright Jupiter and Saturn are set against the stars of Capricornus.

By two hours after sunset. Jupiter and Saturn are higher in the southeastern sky.  They are retrograding in Capricornus.  This apparent westward motion compared to the distant stars is an illusion from our faster moving planet moving between the sun and the planet.  Jupiter appears at opposition every 399 days, while the slower moving Saturn is opposite the sun in the sky every 378 days.

This evening, use a binocular to spot the dimmer stars with the giant planets.  Saturn is 1.0° to the lower right of Upsilon Capricorni (υ Cap on the chart).  Jupiter is 3.4° to the upper right of Iota Aquarii (ι Aqr), 0.7° to the lower right of Mu Capricorni (μ Cap) and 2.3° to the upper left of Deneb Algedi.

Follow them westward during the night.  The moon rises around midnight.  Jupiter and Saturn set long before sunrise tomorrow morning.

Detailed Daily Note:The moon (22.8d, 39%) is over 56° above the east-southeast horizon. For the second time this month, the thick crescent is caught between the horns of the Bull.  It is 4.9° to the lower right of Elnath and 5.3° to the upper right of ζ Tau. Twenty-five minutes after sunset, Mercury is about 4° up in the west, 16.0° to the lower right of Venus. Use a binocular.  Twenty minutes later, Venus is about 8° up in the west-southwest, 5.8° to the right of Spica. Through a telescope, Venus is an evening gibbous, 73% illuminated and 15.1” across. The planet sets 89 minutes after sunset, 10 minutes before the end of evening twilight. Saturn is farther eastward along the ecliptic.  It is over 18° above the southeast horizon.  Jupiter is 17.6° of ecliptic longitude to the east of Saturn and 127.1° of ecliptic longitude east of Venus.  The Jovian Giant is over 12° up in the east-southeast.  Two hours after sunset, Saturn, nearly 26° up in the south-southeast, is 1.0° to the lower left of υ Cap.  Jupiter – over 23° above the east-southeast horizon – is 3.4° to the upper right of ι Aqr, 0.7° to the lower right of μ Cap, and 2.3° to the upper left of Deneb Algedi.

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