2024, September 9: Mercury-Regulus Conjunction, See Nightly Planet Parade

September 9, 2024:  A Mercury-Regulus conjunction occurs in the eastern sky before sunrise.  Mercury, Venus, Mars, Jupiter, and Saturn are visible during the nightly planet parade.

Venus, Mercury, Regulus, September 11, 2023
Photo Caption – Venus, Mercury, Regulus, September 11, 2023

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by Jeffrey L. Hunt

Chicago, Illinois: Sunrise, 6:25 a.m. CDT; Sunset, 7:10 p.m. CDT.  Check local sources for sunrise and sunset times. Times are calculated by the US Naval Observatory’s MICA computer program.

Mercury-Regulus Conjunction

Mercury’s September Morning Appearance
Chart Caption – 2024, September 9: Mercury passes 0.5° to Regulus’ upper left, a Mercury-Regulus conjunction.

A Mercury-Regulus conjunction occurs in the eastern sky before sunrise.  As the speedy planet retreats into brighter twilight, it passes 0.5° to Regulus’ upper left, the brightest star in Leo.  While the pair appears close in the sky, Mercury is nearly 97 million miles away and Regulus is nearly 80 light years distant.

At 45 minutes before sunrise, find the conjunction about 8° up in the east-northeastern sky.  Find a clear view in that direction.  A hilltop or elevated structure helps to see over obstacles.

Mercury’s September Morning Appearance
Chart Caption – 2024, September 10-14: Mercury’s changing separation from Regulus, Leo’s brightest star, as the innermost planet disappears into twilight.

Regulus and the Lion are emerging from their solar conjunction.  They appear higher in the sky each morning while Mercury opens a wider gap to the star.

Mercury is the final bright planet to appear in the sky during the nightly planet parade that begins after sunset with Venus in the western sky.

This morning four bright planets and two dim worlds are lined up along the solar system’s plane – known as the ecliptic – from the east-northeast to the west-southwest.

Jupiter and Mars

Mercury-Regulus conjunction Nightly planet parade
Chart Caption – 2024, September 9: Jupiter and Mars are high in the southeast before sunrise.

Bright Jupiter gleams from high in the southeastern sky.  It is the brightest starlike body in the sky this morning.  To the unassisted eye, even the solar system’s largest planet appears as a star.  A binocular may reveal a few of its largest moons.

The Jovian Giant plods eastward between Elnath and Zeta Tauri, Taurus’ horns.  The planet is slowing to begin to retrograde next month.  This morning, Jupiter is 10.5° to the left of Aldebaran, the Bull’s brightest star.

Track Mars

Mars, resembling Aldebaran’s brightness and color, marches eastward near Castor’s foot, nearly 13° to Jupiter’s lower left.  It is 1.4° to the upper right of Propus.

Mars marches into Gemini
Chart Caption – 2024, September 5-15: Through a binocular, Mars passes the star cluster Messier 35 and some Gemini stars.

Use a binocular to track the planet’s changing place compared to the stars and explore a star cluster, cataloged as Messier 35 in the same starfield with the planet.

Uranus

Dim Uranus is in the same binocular field with the Pleiades star cluster, that appears to ride on Taurus back.  The planet is slowly retrograding and it moves little from night to night.  See this article for a chart that identifies the planet against the starfield.

Morning Saturn

At this hour, Saturn is about 10° up in the west-southwest.  It is in the sky nearly all night as it is now past opposition, rising a several minutes before sunset and setting before sunrise. 

The Ringed Wonder is in front of a distant dim Aquarius’ starfield.  While not as bright as Jupiter and slightly dimmer than Mars, it is the brightest star in the region.  It continues to retrograde until mid-November.

Neptune

The most difficult planet to see this morning is Neptune.  It is very faint and appears in front of a dim Pisces’ starfield about 12° to Saturn’s upper left.  A binocular is needed to locate the stars as well as the planet. During 2025, after Saturn reappears in the eastern sky from its solar conjunction, it appears in the same binocular field with Neptune, providing a bright reference point for locating the modern solar system model’s most-distant world. A chart to locate Neptune is in this article.

Venus Leads Nightly Planet Parade

Mercury-Regulus conjunction Nightly planet parade
Chart Caption – 2024, September 9: At 30 minutes after sunset, Venus is low in the western sky.

The planet parade begins with the appearance of Evening Star Venus after sundown.  Like Mercury, find a clear horizon looking westward after nightfall.  At 30 minutes after sunset, the planet is about 5° up in the west.

It is bright enough to shine through bright evening twilight.  The planet is approaching Spica, Virgo’s brightest star.  Tonight, the Venus-Spica gap is 10.5°.  In three nights, they appear in the same binocular field.

Waxing Moon with Scorpius

Mercury-Regulus conjunction Nightly planet parade
Chart Caption – 2024, September 9: The moon is with Scorpius after nightfall.

This evening the waxing crescent moon is part of the parade.  At 45 minutes after sundown, it is about 15° above the southwest horizon, 3.4° to Dschubba’s lower left, and 6.5° to Antares lower right. Both stars are part of Scorpius.

Look for Venus, Saturn Simultaneously

Mercury-Regulus conjunction Nightly planet parade
Chart Caption – 2024, September 9: At 45 minutes after sundown, Saturn is in the east-southeast.

At this hour attempt to see Venus and Saturn simultaneously, especially if the sky is exceptionally clear.  Venus is only a few degrees above its horizon, while Saturn is nearly 8° up in the east-southeast.

A Venus-Saturn opposition occurred on August 18th, when Venus set as Saturn rose.  Venus’ visibility suffers from the ecliptic’s low angle with the western horizon after nightfall at this season. While Saturn was in the sky with Venus, bright evening twilight overwhelmed its view.

Beginning tomorrow, Venus sets at Nautical Twilight. When at sea, the horizon is still distinguishable from the sky.  Geometrically, the sun is 12° below the horizon.  This occurs 61 minutes after the sun sets tomorrow.  By month’s end, Venus gains another 15 minutes of setting time compared to sunset, making the sky darker when the two planets are visible at the same time.

Find the Mercury-Regulus conjunction this morning and look for the nightly planet parade during the next week before Mercury disappears into brighter morning twilight.

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