2023, September 16:  Planets on a String, Mars’ Last Hurrah

Photo Caption – Venus, Jupiter, Mars, Regulus, October 25, 2015


by Jeffrey L. Hunt

Chicago, Illinois:  Sunrise, 6:32 a.m. CDT; Sunset, 6:59 p.m. CDT.  Check local sources for sunrise and sunset times. Times are calculated by the US Naval Observatory’s MICA computer program.

Summaries of Current Sky Events
Summary for Venus as a Morning Star, 2023-24

Here is today’s planet forecast:

Morning Sky

Chart Caption – 2023, September 16: Saturn is in the west-southwest during early morning hours.

Two and one-half hours before sunrise, three planets lie along an imaginary arc, starting at the eastern horizon, passing high in the south, and reaching the horizon in the west-southwest.  Venus, Jupiter, and Saturn are along that arc. 

Time is running out to see Venus and Saturn in the sky at the same time until next year after the Ringed Wonder’s solar conjunction and reappearance in the morning sky before Venus leaves.

Begin with Saturn.  At this hour, it is less than 10° above the west-southwest horizon.  The stars that have been referenced in these articles, Skat and Lambda Aquarii (λ Aqr on the chart), are nearby. In another forty-five minutes, the planet is dimmed and blurred by the thick layers of atmosphere near the horizon and very difficult to see.

Chart Caption – 2023, September 16: Bright Jupiter is high in the south before twilight begins.

While looking for Saturn, locate Jupiter, high in the southern sky. The planet is the second brightest star in the sky this morning.

Jupiter is retrograding in front of Aries, 13.5° to the lower left of Hamal, the constellation’s brightest star, 11.2° to the upper right of Menkar, Cetus’ nostril, and 15.9° to the lower right of the Pleiades star cluster, part of Taurus.

As the planet appears to move westward, it crosses an imaginary line from Hamal to Menkar.  Watch the planet during the next several mornings, as it retrogrades.

At this hour, Venus is over 5° above the eastern horizon, completing the string of three planets that spans the sky.

Chart Caption – 2023, September 16: One hour before sunrise, brilliant Venus is in the east with Sirius, Procyon, and Regulus.

As Earth rotates, Saturn sets and Jupiter moves farther westward.  By one hour before sunrise, Venus stands over 20° above the eastern horizon, with Sirius, night’s brightest star, at the same altitude – height above the horizon – in the southeast.  The brightest planet and the brightest star stand in the eastern sky during morning twilight. This continues each morning until month’s end.

Procyon, the Little Dog Star, is above an imaginary line from Venus to Sirius.

Regulus, Leo’s brightest star, stands over 10° above the eastern horizon, 16.2° to the lower left of Venus.  The star generally marks the direction of Venus’ travel.  It is the brightest star that appears closest to the ecliptic – the plane of the solar system where the moon and planets appear to move. Venus passes by on October 9th.  Watch the gap close each morning.

Regulus is the fifteenth brightest star visible from the mid-northern latitudes, but Sirius is nearly fifteen times brighter. It shines from a distance of nearly 80 light years and is nearly 150 times brighter than the sun.

Chart Caption – 2023, September 16: Forty minutes before sunrise, Venus, Mercury and Regulus are in the east.

By forty minutes before daybreak, Mercury is over 5° above the eastern horizon and slightly less than 8° to the lower left of Regulus.  Depending on local weather conditions, the planet might be visible to the unassisted eye. 

Chart Caption – 2023, September 16: Through a binocular, in overlapping fields of view, find Mercury and Regulus.

Use a binocular to find Regulus and the planet.  They are too far apart to fit into the same field of view.  So, find one of them and then move the binocular slightly to see the other.

Evening Sky

Chart Caption – 2023, September 16: After sunset, find Mars and the crescent moon in the western sky through a binocular.

The crescent moon, 3% illuminated, celebrates Mars’ last hurrah in the western sky after sundown.  With a binocular find the razor-thin crescent and the very dim planet less than 5° up in the sky about 10° to the left (south) of the west cardinal direction.

The Red Planet is on a slow slide into bright sunlight.  Since about a month ago, no celestial landmark has been nearby to cue us where to look for the planet.

Mars reaches solar conjunction November 18th and begins a slow climb into the morning sky.  It has a conjunction with Mercury January 27, 2024, followed by a Venus conjunction February 22nd.

Chart Caption – 2023, September 16: Saturn is in the southeast during early evening hours.

Two hours after sundown, Saturn is over 25° up in the southeast.  This is the beginning of the planets-on-a-string display that ends with three planets spanning the sky as described in the morning section.

Saturn continues to retrograde in front of Aquarius, 9.4° to the upper right of Skat, the Aquarian’s leg, and 9.7° to the right of Lambda Aquarii (λ Aqr on the chart).  Retrograde continues until November 4th.

Jupiter rises about two hours after sunset and seems to follow Saturn westward.  By tomorrow morning, the three planets are again strung across the ecliptic’s arc from east to west-southwest.


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