2023, January 12: Mars’ Retrograde Ends, Western Planets in Line


January 12, 2023: Mars resumes its eastward march in Taurus tonight.  With Mars in the east, Venus, Saturn, and Jupiter are in a line in the western sky.

Photo Caption – 2022, February 26: Venus, Mars, and the moon before sunrise in the southeast.


by Jeffrey L. Hunt

Chicago, Illinois:  Sunrise, 7:17 a.m. CST; Sunset, 4:41 p.m. CST.  Check local sources for sunrise and sunset times for your location.  Times are calculated from the U.S. Naval Observatory’s MICA computer program.

The sunrise time is moving earlier every few days.  By month’s end the sun rises at 7:04 a.m. CST in Chicago.

Jupiter’s Great Red Spot’s transit times, when it is in the center of the planet in the southern hemisphere: 4:27 UT, 14:23 UT; Jan. 13, 0:19. Convert the time to your time zone. In the US, subtract five hours for EST, six hours for CST, and so on.  Use a telescope to see the spot.  Times are from Sky & Telescope magazine.

The window to see the Red Spot is narrowing.  Jupiter starts the evening in the south-southwest and sets nearly six hours after sundown.  When the planet’s altitude – height above the horizon – is below about 30°, the planet’s image is blurred by Earth’s atmosphere.  The planet’s light travels through a thicker atmospheric layer when it is lower in the sky.  We see this great distortion in the reddening of the misshaped sun near the horizon. The window for a clear view at Jupiter is about four hours long.  With the planet spinning about every ten hours, the occurrences of viewing the long-lived storm during this appearance are lessening. Later in the spring, Jupiter disappears into bright evening twilight, reappearing in the eastern sky before sunrise later in the year.  Red Spot observing begins again at that time.

Chart Caption – From north of the solar system, Earth and Mars relative orbits are shown. The line of sight from Earth to Mars indicates the Red Planet’s appearance against the distance stars.

Mars’ retrograde ends for this opposition season tonight.  Retrograde motion is an illusion as Earth passes an outer planet.  On the annotated orbit above, the line of sight from Earth to Mars moves eastward or counterclockwise on the chart as Earth approaches the planet.  The planet appears to move eastward against the starfield.  On October 30, 2022, the line of sight began to shift clockwise on the chart. While Mars does not stop moving eastward in its orbit, it seems to move westward as that line of sight shifts westward.  Tonight, that line of sight begins to move eastward again and Mars resumes its eastward march through the stars.

Chart Caption – This chart shows the apparent motion of Mars against Taurus. Retrograde motion ends tonight.

On the annotated star chart, the Red Planet’s apparent motion is shown against the starry background.  Unlike a terrestrial map, east is to the left on the chart and west is to the right.  Earlier in the year Mars seemed to move eastward as Earth began to catch Mars.  On October 30th, when the line of sight shifts westward, the planet appears to stop moving eastward and it appeared to move westward or retrograde.  This evening the planet stops retrograding and resumes its eastward trek.

Here is today’s planet forecast:

Morning Sky

Chart Caption – 2023, January 12: The moon is below Leo’s brightest stars, near the Virgo border.

One hour before sunrise, the waning gibbous moon, 75% illuminated, is about halfway up in the southwest, 9.2° to the lower left of Denebola, meaning “the lion’s tail.”

This is the third morning that the moon appears in front of Leo’s stars.  The constellation is a westward-facing lion that we see in silhouette.  To the west is a backwards question mark or a sickle with bright Regulus at the bottom.  To the east is a small triangle.  The eastern bright star is the tail.

The lunar orb is near the Leo-Virgo constellation border.  The star Zavijava – meaning “the corner of the barking dog” – is 5.6° to the moon’s left and part of Virgo. Tomorrow morning, the moon is in front of Virgo, between Zavijava and Porrima.

Mercury is racing into the morning sky, rising at least eight minutes earlier each morning.  This morning it rises 56 minutes before the sun.  It will be visible, but a challenge to see, in about three mornings, getting easier to see through the remainder of the month.

Evening Sky

Chart Caption – 2023, January 12: Venus, Saturn, and Jupiter are in the western sky after sunset.

Three of the four bright planets are lined up in the southwestern sky after sundown.  At forty-five minutes after the sun sets, brilliant Venus is less than 10° up in the west-southwest.  It appears farther north along the horizon each evening. 

The Evening Star sets later each night and is heading toward Saturn for a January 22nd conjunction.  This evening, Venus is 11.3° to the lower right of the Ringed Wonder.

Saturn is slowly moving eastward in eastern Capricornus. At Saturn’s slow plod, it moves only one-tenth Venus’ change from night to night.

Venus’ meeting with Jupiter is the second bright conjunction of 2023.  Venus catches and passes the Jovian Giant on March 1st.

Chart Caption – 2023, January 12: Mars is visible in the east, to the upper left of Aldebaran.

Farther eastward, Mars ends its retrograde in front of Taurus, 8.5° to the upper left of Aldebaran.  At this hour find the Red Planet halfway up in the eastern sky.

Chart Caption – 2023, January 12: At an hour after sundown, Taurus is seen behind Mars.

As the sky darkens further, Taurus’ stars are visible behind Mars.  Aldebaran and the Hyades star cluster form the Bull’s head.  A binocular may be necessary to see the “V” pattern.  The horns are dotted by Elnath and Zeta Tauri. Resembling a tiny dipper, the Pleiades star cluster rides on the Bull’s back.  This is an impressive stellar bundle of mostly blue stars through a binocular.

Chart Caption – 2023, January 12: Through a binocular, Saturn is in front of stars of eastern Capricornus.

Farther westward through the binocular, Saturn is 1.3° to the right of Deneb Algedi.  Notice that the Ringed Wonder is passing dim 45 Capricorni (45 Cap on the chart).  The separation is only 0.2°.

Jupiter (NASA Photo)

At 6:19 p.m. CST, the Great Red Spot is visible through a telescope.  The planet is about 45° up in the southwest, a favorable place for a good view from the central US.  At this time, Jupiter’s large satellite Europa is visible against the cloud tops. As Jupiter spins and the satellite revolves, Europa moves from in front of the planet at 6:35 p.m. At about that time, the satellite’s shadow is cast on the cloud tops.  This continues until nearly 9 p.m. CST.



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