2023, August 12: Morning Crescent Moon, Star Cluster, Sirius Heliacal Rising in Chicago


August 12, 2023: A thin crescent moon appears near the foot of Gemini’s Castor foot and a star cluster.  This morning, Sirius makes its first appearance for sky watchers at Chicago’s latitude.

Chart Caption – 2023: Sirius first appears above the horizon to the unaided eye on August 12th in Chicago.


by Jeffrey L. Hunt Chicago, Illinois: 

Sunrise, 5:56 a.m. CDT; Sunset, 7:55 p.m. CDT.  Check local sources for sunrise and sunset times.

2020, August 14: Sirius clears the horizon minutes before sunrise. The star is visible through binoculars and a short time exposure, but not with the unaided eye.

Sirius makes its first appearance this morning at Chicago’s latitude based on Jean Meeus’ equations.  The star is low in the east-southeast about forty minutes before sunrise. While today is the theoretical first appearance, the star may be hidden on the horizon by clouds, trees, or other terrestrial obstructions. A view across Lake Michigan, especially from a high-rise building, provides an ideal natural horizon. First attempt to locate Sirius with a binocular and find it without the optical help.

Photo Caption – A Perseid meteor, photographed with a camera that views the entire sky. (NASA photo)

The Perseid meteor shower peaks before twilight begins tomorrow morning.  The shower’s origin is the dust and debris from Comet 109P/Swift-Tuttle.  The sun’s light vaporizes the comet’s ices, releasing dust particles that are widely distributed along the orbital path.  Each year, Earth passes through the debris, the dust enters the atmosphere, and vaporizes around 50 miles above the ground.

In this 30 second exposure, a meteor streaks across the sky during the annual Perseid meteor shower Friday, Aug. 12, 2016 in Spruce Knob, West Virginia. Photo Credit: (NASA/Bill Ingalls)

The predicted maximum visible rate before sunrise on the morning of the 13th is ninety meteors per hour.  What is seen depends on the sky darkness and how much of the sky is visible to any single meteor watcher. Urban and suburban sky watchers may see approximately ten meteors each hour, while those in the countryside might see twenty to thirty per hour.

The shower’s center or radiant is in Perseus.  It rises high in the sky from Earth’s rotation after midnight when we view the meteor shower head-on.

Photo Caption – A meteor watch party (By Open AI)

To maximize the meteor count recruit four other friends for a Saturday night through Sunday morning meteor watch.  One watcher looks overhead, where more meteors appear.  The others look toward each cardinal direction, because the meteors can be seen anywhere in the sky.

Summaries of Current Sky Events

Here is today’s planet forecast:

Morning Sky

Chart Caption – 2023, August 12: The moon is near Castor’s foot during morning twilight.

An hour before sunrise, a thin crescent moon, 14% illuminated, is over 30° above the east-northeast horizon.  It is near Castor’s foot, 5.7° to the left of Propus, the toe, and 5.1° to the upper left of Tejat Posterior, the heel.

Photo Caption – 2020, December 11: About an hour before sunrise, the crescent moon that is 14% illuminated is in the southeastern sky.

The moon is showing a beautiful display of earthshine between the lunar cusps or horns.  The effect is from sunlight reflecting from Earth’s oceans, clouds, and land.  It gently illuminates the lunar night.

Chart Caption – 2023, August 12: Through a binocular, the moon is visible with the star cluster Messier 35 (M35) and Castor’s foot.

The moon appears in the same binocular field of view with the star cluster Messier 35 (M 35 on the chart.)  The cluster has over 100 stars, shining from a distance of 2,800 light years.  From the countryside, it can be seen without optical assistance as a blurry patch of light.

Chart Caption – 2023, August 12: Jupiter is high in the southeast before sunrise.

At this hour, bright Jupiter is high in the southeast, 13.2° to the lower left of Hamal, Aries’ brightest star, and 11.3° to the upper left of Menkar, in Cetus.  The Pleiades star cluster is to the left. Jupiter is slowly moving eastward against Aries.  It is 8.3° to the west of Uranus.  The Jovian Giant begins to retrograde on September 4th, short of the two planets fitting into the same binocular field of view.

Chart Caption – 2023, August 12: During morning twilight, Saturn is in the southwest.

At this hour Saturn is low in the southwest.  While not as bright as Jupiter, it is brighter than most stars in the sky this morning. The planet is retrograding in front of Aquarius, 7.6° to the right of Skat and 7.1° to the lower right of Lambda Aquarii (λ Aqr).  Use a binocular to see the dim stars, especially from urban and suburban areas.

Evening Sky

Photo Caption – This picture of Venus was taken by the Galileo spacecraft (NASA)

Tomorrow Venus passes between Earth and the sun, known as inferior conjunction.  The brilliant planet then jumps into the morning sky, rising nearly two hours before the sun at month’s end.

Photo Caption – Mercury as Never Seen Before. (NASA photo)

Mercury is retreating back into sunlight and fading in brightness.  It sets only fifty-four minutes after sundown.

The Red Planet from the Mars Global Surveyor shows the effects of a global dust storm (NASA)

Mars is washed out by evening twilight.  This evening it is the dimmest of the five bright planets. If it were visible it would rank about 35th on a stellar brightness list.

Chart Caption – 2023, August 12: Two hours after sunset, Saturn is in the east-southeast.

Nearing its opposition, Saturn rises in the east-southeast, less than forty minutes after sundown.  At opposition, when Earth is between the Ringed Wonder and the sun, Saturn rises at sunset.  It rises about three minutes earlier each evening.

By two hours after sunset, Saturn is nearly 15° above the east-southeast horizon.  Find it in the south four hours later, and in the southwest tomorrow morning.

Jupiter rises in the east, less than three hours after Saturn.



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