2023, July 10: Mars-Regulus Conjunction


July 10, 2023: Mars passes closely to Regulus in the western sky after nightfall in a biennial event.  Venus, Mars, and Regulus make a compact grouping.

Photo Caption – 2023, July 10: Mars-Regulus conjunction with Venus nearby.


by Jeffrey L. Hunt

Chicago, Illinois:  Sunrise, 5:25 a.m. CDT; Sunset, 8:27 p.m. CDT.  Check local sources for sunrise and sunset times for your location.  Times are calculated by the U.S. Naval Observatory’s MICA computer program.

Summaries of Current Sky Events

Here is today’s planet forecast:

Morning Sky

Chart Caption – 2023, July 10: Bright Jupiter and the thick crescent moon are in the eastern sky before daybreak.

The thick crescent moon, 46% illuminated, is less than halfway up in the southeast an hour before sunrise.  It rises after midnight and about seven hours before the sun.  Each morning the moon is farther eastward and the crescent is thinning or waning.

This morning, Jupiter is nearly one-third of the way up in the east-southeast and less than 20° to the lower left of the moon.  The Jovian Giant is slowly moving eastward in front of Aries, 11.4° to the lower right of Hamal, the constellation’s brightest star.  Notice the star Menkar, the sea monster’s nostril, about halfway from the planet to the horizon.

Photo Caption – Jupiter (NASA Photo)

At this hour, Jupiter’s Great Red Spot is about to disappear from the planet’s rapid rotation.  Through a telescope, it appears at the center of the planet in the southern hemisphere at 3:35 a.m. CDT.

During morning twilight, Saturn is nearly 40° up in the south.  The Ringed Wonder rises in the southeast before midnight.

Chart Caption – 2023, July 10: Saturn is in the south above Fomalhaut before sunrise.

Saturn is retrograding in front of dim Aquarius, washed out by the growing twilight and the perpetual glow of outdoor lighting in urban and suburban settings.  Retrograde is an illusion from the line of sight from Earth through Saturn and to the stars that shifts westward.  We see the planet farther west against the starry background.  Spot Deneb Algedi, in Capricornus, nearly 13° to Saturn’s lower right and Fomalhaut, part of the southern fish, is about halfway from the planet to the horizon.

Evening Sky

Chart Caption – 2023, July 10: Venus, Mars, Regulus, and Leo are low in the west after sundown.

After sundown, Mars passes Regulus, Leo’s brightest star, in the western sky.  Mars has a conjunction with the star nearly every two years (on average 20 days short of two years).

Last night Venus, Mars, and Regulus formed the most compact group until 2053.

Venus is “that bright star” in the western sky as night falls.  It is in its interval of greatest brightness. If you have been watching Venus in the evening sky, you have observed that it is noticeably brighter than it was six weeks ago.  The Evening Star is lower in the sky as well. It sets three to four minutes earlier each evening compared to sunset.  It passes between our world and the sun on August 13th.

Chart Caption – 2023, July 10: Venus, Mars, and Regulus appear in the same binocular field of view.

The Venus-Mars-Regulus trio fits into the same binocular field of view.  This helps identify dimmer Mars and Regulus compared to Venus’ location.  This evening Regulus is 4.3° to the upper left of Venus and 0.7° below Mars.

Regulus is the brightest star in a westward-facing Lion that we see in silhouette.  The star is at the bottom of a sickle or backwards question mark, outlining the animal’s head.  A triangle of stars makes the haunches and star dotted by Denebola.

During the next few days, Mars moves away from Venus and Regulus, while Venus closes in on the star.  In six evenings, Venus approaches to 3.5°, but no conjunction occurs.

Mercury is entering the scene.  This evening it sets nearly fifty minutes after sunset.  The evening crescent moon comes through the region on the 19th and 20th, making a celestial traffic jam in the western sky.

Watch the changing positions of Venus and Mars compared to Regulus each clear evening.



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