Planet Watch: October-December 2023

Solar system showing relative size of (but not distance between) planets.

Keep tabs on our planets with Morrison Planetarium's quarterly guide to planetary activity.

Mercury

At the beginning of October, Mercury rises about an hour before sunrise and is already well past greatest western elongation, becoming gradually more difficult to see low in the east as it retreats into the morning twilight. Moving to the far side of the Sun and passing superior conjunction on October 19th, it moves to the eastern side of the Sun and becomes visible in the evening sky around late-November, reaching greatest eastern elongation on December 4, when its angular separation from the Sun is at a maximum of 21.3°. Returning to the Sun's glare, it swings between Earth and the Sun, reaching inferior conjunction on December 22.

The Moon passes near Mercury in the sky on October 14, but both are too close to the Sun to be observed in the glare. Their encounters on November 14 and December 13—both very low in the southwest soon after sunset—are slightly more separated from the Sun.

Venus

The brightest planet is a morning object all season, reaching greatest brilliancy on September 18 and appearing as a thick, waxing crescent through telescopes and binoculars.

The Moon appears about 5° from Venus, located in the east just before dawn on October 10, with the added bonus of the star Regulus—the heart of Leo the Lion—between them. Their next pairing on November 9 is even closer (less than 2°) against the stars of Virgo the Maiden, and the last meeting of the season on December 9 brings them about 3.5° from one another near the boundary between Virgo and Libra the Scales, located in the southeast before sunrise.

Mars

For most of the season, Mars is buried in the glow of the Sun. Barely visible very low in the west just after sunset at the beginning of October, it and the Sun both appear to slowly move eastward against the stars, with Mars obscured in the glare the whole time. Reaching conjunction on November 17, Mars moves to the west of the Sun and into the morning sky, but doesn't appear out of the glow until February.

The Moon's close passes near Mars on October 15, November 12-13, and December 11 are all washed from view by our star's glare.

Jupiter

On October 1, Jupiter rises about 2 hours after sunset against the stars of Aries the Ram. It is already quite bright as it approaches opposition, which occurs on November 3. This is when it rises at sunset and is visible all night at its largest and brightest as seen from Earth. Small telescopes and even tripod-mounted binoculars reveal the giant planet's disk and four largest moons, which were discovered by Galileo in 1610. Following opposition, Jupiter climbs gradually higher in the east at nightfall.

The Moon joins Jupiter on the nights of October 1, October 28, November 24, and December 21, all against the stars of Aries the Ram.

Saturn

Visible low in the southeast at nightfall, Saturn loiters against the stars of Aquarius the Water-Carrier for about the next year-and-a-half. In October, it is in retrograde motion, slowly creeping from east to west against the stars until the end of October, although this motion is hardly noticeable, amounting to less than 1° of arc (or twice the apparent diameter of a full Moon). Saturn stops (is stationary) on November 4 and resumes its normal prograde motion, plodding from west to east again and ending the year less than 2° from where it began the season. On November 1, it is located in the south-southeast at nightfall, and on December 1, it's due south an hour after sunset.

The Moon appears near Saturn on the nights of October 23, November 20, and December 17, against the stars of Aquarius the Water-Carrier.