2023, September 17: Moon-Spica Conjunction, Morning Planet Lineup

September 17, 2023: The moon passes Spica after sunset.  Venus, Jupiter, and Saturn are in a lineup during early morning hours.

Venus, Jupiter, Mars, Regulus September 26, 2015
Photo Caption – Venus, Jupiter, Mars, Regulus September 26, 2015

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by Jeffrey L. Hunt

Chicago, Illinois:  Sunrise, 6:33 a.m. CDT; Sunset, 6:57 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

2023, September 17: Saturn is low in the west-southwest during early morning hours.
Chart Caption – 2023, September 17: Saturn is low in the west-southwest during early morning hours.

Two and one-half hours before sunrise, Venus, Jupiter and Saturn seem to be hanging on the arc of the ecliptic, the plane of the solar system, beginning at the eastern horizon, through high in the south, and ending in the west-southwest.  Saturn, the most difficult planet to see this morning is less than 10° above the west-southwest horizon. As during the evenings, Skat and Lambda Aquarii (λ Aqr on the chart) are nearby.

2023, September 17: Jupiter is high in the south before morning twilight begins.
Chart Caption – 2023, September 17: Jupiter is high in the south before morning twilight begins.

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

During the next few weeks, as Jupiter seems to move westward compared to the starfield, watch it cross and imaginary line from Hamal to Menkar.

At this hour, brilliant Venus is low in the eastern sky.  This planet is easy to locate, even when near the horizon.  It appears higher as morning progresses, but Saturn disappears into the haze near the horizon and then setting at the west-southwest horizon.  Bright Jupiter appears farther westward, but it is still relatively high in the sky.

On October 10th, Venus and Saturn are 180° apart in the sky.  Saturn sets as Venus rises.  While Saturn is dimmed by the haze near the horizon, it may not be visible when Venus rises for several mornings before the opposition date.  What is the last date you see them in the sky at the same time?

2023, September 17: Venus, Sirius, Procyon, and Regulus are in the eastern sky during morning twilight.
Chart Caption – 2023, September 17: Venus, Sirius, Procyon, and Regulus are in the eastern sky during morning twilight.

By an hour before sunrise, Venus is over 20° above the east horizon and 15.7° to the upper right of Regulus, Leo’s brightest star, meaning “the prince.”  Venus is moving in Regulus’ direction, passing the star October 9th.  Watch the gap between them shrink each morning.

The Venus-Sirius display continues.  Sirius, known as the Dog Star, is the brightest nighttime star.  It is too far away from the plane of the solar system, known as the ecliptic, to have a planetary or lunar conjunction.  We see Venus and Sirius at the same altitude – height above the horizon – and 40° apart.  Venus is in the east and Sirius in the southeast.  This continues through the month.

2023, September 17: Forty-five minutes before sunrise, Mercury is low in the east below Regulus.
Chart Caption – 2023, September 17: Forty-five minutes before sunrise, Mercury is low in the east below Regulus.

Mercury, beginning its best morning appearance of the year, is over 6° above the eastern horizon at forty-five minutes before daybreak.  It brightens each morning.  Find it first with a binocular, 8.1° to the lower left of Regulus.  Yesterday, Mercury was closer to the star.

Mercury reaches its largest separation from the sun, known as greatest elongation, on the 22nd.  The plane of the solar system is tipped very favorably to see the inner-most planet as it sprints out of bright sunlight.

Evening Sky

2023, September 17: Thirty minutes after sunset, the crescent moon is with Spica.
Chart Caption – 2023, September 17: Thirty minutes after sunset, the crescent moon is with Spica.

The crescent moon, 8% illuminated, is about 6° up in the west-southwest at thirty minutes after sundown.  It is 3.3° to the upper left of Spica.  Look for them with a binocular.

Unlike the morning sky, the seasonal presentation of the ecliptic is unfavorable during September evenings.  It makes a very shallow angle with the horizon.  Spica is 2° below the solar system plane and it is not so easy to see during September evenings.  Spica appears behind the sun in about a month, reappearing in the morning sky.  Venus passes the star November 29th.

2023, September 17: Two hours after sunset, Saturn is in the southeast with Skat and Lambda Aquarii.
Chart Caption – 2023, September 17: Two hours after sunset, Saturn is in the southeast with Skat and Lambda Aquarii.

This evening, Saturn leads the planet display that occurs each morning before twilight begins.  The Ringed Wonder rises before sunset and appears over 25° up in the southeast two hours after sundown. It 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.

Here’s another reminder to find a telescope night sponsored by a local science museum or astronomy club to see Saturn.  Search Sky & Telescope’s database for a source in your region. Or talk with your neighborhood sky watcher for a peek at Saturn through their telescope.

An hour after spotting Saturn, Jupiter is about 10° up in the east.  During the night they are farther westward reaching their places in the morning to have Venus join them from the eastern sky.

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