September 22, 2023: Mercury is at its best morning view of the year. After sundown, the moon appears above the Teapot’s spout.
by Jeffrey L. Hunt
Chicago, Illinois: Sunrise, 6:38 a.m. CDT; Sunset, 6:48 p.m. CDT. Check local sources for sunrise and sunset times. Times are calculated by the US Naval Observatory’s MICA computer program.
Today, the sun is in the sky for twelve hours, ten minutes.
The Autumnal Equinox occurs at 1:50 a.m. CDT tomorrow morning. At this moment, the sun is at longitude 180° along the ecliptic; that is, 180° from the origin of the coordinate system that is the Vernal Equinox, the sun’s location on the first day of spring in the northern hemisphere. At the moment of the equinox, the sun appears to be on the celestial equator, a circle in the sky directly above Earth’s equator.
Because of the definition of sunrise and sunset and the bending of light when the sun is near the horizon, daylight and nighttime are not equal tomorrow. September 25th and 26th are the days when the twenty-four-hour day is almost – within a minute – equal between sunlight and nighttime.
The moon is at its First Quarter phase at 2:32 p.m. CDT. From Chicago, the moon rises nearly ten minutes later.
Summaries of Current Sky Events
Summary for Venus as a Morning Star, 2023-24
Here is today’s planet forecast:
Morning Sky
Mercury is at its largest separation from the sun today, known as greatest elongation. Geometrically, Earth is at the vertex of an angle that extends from the sun to Mercury. The angle measures 17.9°. This value is about 10° smaller than the planet’s largest value. Mercury’s orbit is highly elliptical and this morning the planet is near perihelion, the closest point to the sun.
The planet’s location in the sky is highly favorable because of the high angle the plane of the solar system makes with the horizon. The planet’s best morning views occur during the autumn season from this favorable angle.
While Mercury is at its best, it is low in the eastern sky. An hour before sunrise, the speedy planet is over 5° above the horizon and 11.2° to the lower left of Regulus.
Mercury is fairly bright, although dimmer than Venus, Sirius, and Jupiter. Find a clear eastern horizon and locate the planet. As Mercury begins to retreat back into the sun’s glare, it continues to brighten.
At this hour, brilliant Venus is over 25° above the eastern horizon and 13.1° to the upper right of Regulus. The Morning Star is stepping eastward, passing the star October 9th. Watch this gap close on each clear morning.
Notice Sirius in the southeast, at about the same altitude – height above the horizon – as Venus and about 40° to the right of the planet.
Procyon, the Little Dog Star, is above an imaginary line from Venus to Sirius.
At this hour, bright Jupiter is high in the southwest. It is retrograding in front of Aries, approaching an imaginary line from Hamal, the Ram’s brightest star, and Menkar, the Sea Monster’s nostril.
The Jovian Giant appears to move westward compared to the starfield. This is an illusion as our world approaches and passes between a distant solar system body and the sun.
Look again for Mercury to see it slightly higher in the sky as twilight continues.
Evening Sky
Dim Mars is slowly sliding into bright evening twilight heading toward its solar conjunction during November. The planet sets about forty minutes after night fall.
An hour after sundown, the slightly gibbous moon, 52% illuminated, is about 20° up in the south-southwest. It is above the spout of the Teapot, a modern moniker for Sagittarius. The lunar orb is 1.5° to the upper left of Alnasl, the point of the Sagittarian’s arrow. Use a binocular to see the starfield with the moon.
Farther eastward, Saturn is nearly 20° above the southeast horizon, 9.7° to the upper right of Skat, meaning “the leg,” and 10.1° to the upper right of Lambda Aquarii (λ Aqr on the chart). The planet continues to retrograde.
The Ringed Wonder is south before midnight and sets in the west-southwest nearly three hours before sunrise tomorrow morning.
Bright Jupiter rises less than two hours after sundown. By midnight it is over 30° up in the east-southeast. Tomorrow morning it is again high in the southwestern sky.
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