August 18, 2024: Mercury is at inferior conjunction today, between Earth and Sun at 8:58 p.m. Central Time.
by Jeffrey L. Hunt
Mercury at Inferior Conjunction
Mercury passes between Earth and Sun, known as inferior conjunction, at 8:58 p.m. Central Time. The planet is not precisely between the two bodies, otherwise sky watchers would see Mercury appear to pass across the face of the sun.
Mercury does not revolve around the sun in the same plane that is made by Earth and Sun, known as the ecliptic. Its orbit is tilted 7.0° compared to that plane. Two days ago, the planet reached its most-southerly point below the plane.
At this inferior conjunction, Mercury is 4.5° south of the line from our home planet and the central star.
Mercury retrogrades as it moves from the evening sky to a morning view, a west-to east-motion. This ends in 10 mornings when the planet is over 10° above the eastern horizon at sunrise, when it is 14° west of the sun.
See Mercury During September
Mercury reaches the largest separation from the sun, known as greatest elongation, on September 4th, 18.0° west of the central star.
The ecliptic makes a large angle with the horizon before sunrise at this season. While the Sun-Mercury separation is relatively small, the speedy planet rises over 92 minutes before daybreak, standing nearly 8° above the horizon about 45 minutes later.
On this morning, Regulus is emerging from its solar conjunction. It is over 5° to Mercury’s lower left. A binocular is needed to see the star.
Mercury-Regulus Conjunction
Mercury passes 0.5° to Regulus’ upper left five mornings later. While Mercury is bright, use a binocular to see the pair, less than 10° above the eastern horizon at 45 minutes before sunrise.
As the planet recedes into bright morning twilight, it brightens, but it is low in the sky. At midmonth, Mercury is less than 5° above the horizon during mid-twilight, over 10° to Regulus’ lower left.
Mercury continues to plunge into brighter morning twilight, passing on the far side of the sun on September 30th.
Mercury returns to the morning sky again during December, when it has an appearance that is slightly higher in the morning sky during the Christmas season.
Look for Mercury during its appearance during early September.
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