2021, August 14: Waxing Moon, Stellar Double


August 14, 2021: This evening the waxing moon is near Zubenelgenubi, the southern claw, that is a stellar double.  Use a binocular to see both stars that are in a gravitation dance.

Chart Caption – 2021, August 14: Use a binocular to spot Zubenelgenubi with the moon. The star is a binary star. The dimmer second star is immediately to the upper right of the brighter primary.

by Jeffrey L. Hunt

Chicago, Illinois:  Sunrise, 5:58 a.m. CDT; Sunset, 7:52 p.m. CDT.  Check local sources for sunrise and sunset times for your location.

Depending on local observing conditions, Sirius might be visible from low in the east-southeast about 45 minutes before sunrise?  Mid-August is the time of the first appearance of the night’s brightest star from mid-northern latitudes.

Additionally, the variable star Mira is reaching its brightest light. Not one of the brightest stars, it is visible to the unaided eye in the morning sky.

This evening the crescent moon, nearing its first quarter phase, is less than one-third of the way up in the southwestern sky.  Note that the waxing moon is 0.9° to the upper right of Zubenelgenubi – “the southern claw.”  Use a binocular to see the star with the thick crescent moon.

Notice through the binocular that Zubenelgenubi is two stars, a binary star.  Two stars are locked together in a mutual gravitational ballet. The companion is dimmer than the brighter star that is visible to the unaided eye.  In the binocular field, the secondary star is immediately to the upper right of the brighter primary star.

The stellar pair’s distance has been measured at 65 light years.  The two stars are separated by a distance of at least 4,500 times the Earth-Sun distance.

Zubenelgenubi and Zubeneschamali, “the northern claw,” are part of the classic Scorpion.  Today, they are part of Libra, the Scales, the only non-living entity that fashions the background where the sun, moon, and planets appear, the zodiac.

Early in the evening, note the location of brilliant Venus to the lower right of the moon in the western sky.  Bright Jupiter is low in the east-southeast, while Saturn is higher in the southeast.

Detailed Daily Note:Have you spotted Mira?  Look for it before the beginning of morning twilight. One hour before sunrise. During morning twilight, have you seen Sirius gleaming low in the east-southeast? One hour before sunrise, bright Jupiter is 16.0° up in the southwest.  Retrograding in Aquarius and nearing the border with Capricornus, the Jovian Giant is 1.4° to the lower right of ι Aqr, 1.8° to the lower left of Mu Capricorni (μ Cap, m = 5.1), and 4.3° to the upper left of Deneb Algedi.  Forty-five minutes after sunset brilliant Venus (m = −4.0) is about 8° up in the west, 1.0° to the upper left of Zavijava.  This evening’s gap with Spica is 25.6°, as Venus continues to move nearly 1.2° eastward in ecliptic longitude from evening to evening.  Spica is nearly 15° above the west-southwest horizon.  The moon (6.5d, 43%) is nearly 24° above the southwest horizon, 0.9° to the upper right of Zubenelgenubi (β Lib, m = 2.8).  As the sky darkens further, try to spot the star and the moon without optical aid.  Because of the moon’s growing brightness, a binocular assist may be necessary to see them separately.  Farther eastward, Saturn is nearly 13° up in the southeast.  Jupiter is over 5° above the southeast horizon.  Two hours after sunset, Saturn – retrograding in Capricornus and over 22° above the southeast horizon – is 4.9° to the upper right of θ Cap and 1.6° to the lower left of υ Cap. Jupiter, to the lower left of Saturn, is over 17° up in the southeast.

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