Astronomy Essentials

Mercury – up before sunrise – start watching now

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December 27, 2023

Circles showing Earth and Mercury orbits around the sun and 2 red lines from Earth to Mercury and the sun. — At greatest elongation, Mercury appears on one side of the sun as seen from Earth. It’s at its greatest distance from the sun on our sky’s dome. Mercury reaches greatest morning elongation from the sun on January 12, 2024. At that time, it’s 24 degrees from the sunrise. Chart via John Jardine Goss/ EarthSky.

The innermost planet Mercury orbits the sun every 88 days. And Earth is moving, too. So Mercury goes between us and the sun pretty often, about every 116 days. It did this last on December 22, 2023, reaching the point astronomers call inferior conjunction. Since then, Mercury has been speeding ahead of Earth in orbit. And it is now re-emerging in our dawn sky, near the sunrise, below brilliant Venus. Look for it soon! Mercury will reach its greatest morning elongation – its greatest apparent distance from the rising sun – on January 12, 2024.

Due to angle of the ecliptic – path of the sun, moon and planets – this time of the year, this January 2024 Mercury elongation is slightly better viewed from the Southern Hemisphere because Mercury will reach a higher altitude on the sky dome.

The innermost planet – named for the fleet-footed messenger god of the ancient Romans – will be visible into February.

Mercury greatest elongation January 2024

When to watch: Mercury will become visible towards the end of December 2023 in the morning sky. Greatest elongation is – when Mercury will be farthest from the sunrise on our sky’s dome – on January 12. And the planet will remain bright after that. Then, in early February, when it’ll be edging back toward the sunrise, it’ll brighten a little bit making Mercury easier to spot – although low – in the morning twilight.
Where to look: Look in the sunrise direction, as the sky is getting lighter.
Greatest elongation is on January 12 at 15:00 UTC (10:00 a.m. CDT). Mercury is shining at a 0.5 magnitude that morning. And it is 24 degrees from the sun.
Through a telescope on and around January 12, Mercury appears 64% illuminated, in a gibbous phase, and 6.8 arcseconds across.
Note: Once you spot it, notice that Mercury brightens quickly in January, reaching a magnitude of around -0.5 before slipping away in the morning glare in February.

January charts Northern Hemisphere

Mercury in January for viewers in the Northern Hemisphere. — For viewers in the Northern Hemisphere, Mercury lies just above the horizon in the bright twilight shortly before sunrise in January. It’ll reach its greatest evening elongation – farthest from the sun in our morning sky – on January 12, 2024. At best, Mercury reaches 24 degrees from the sun on that day. It’ll brighten slightly after then finally disappearing from the morning sky in February. Also, higher in the morning sky will be the brilliant light of the planet Venus. Chart via EarthSky.

Moon on the mornings of January 8 and 9, 2024, near Antares, Venus and Mercury. — On the mornings of January 8 and 9, the thin waning crescent moon can help guide you to the planet Mercury. Also nearby will be the brilliant planet Venus and the bright star Antares in Scorpius the Scorpion. Chart via EarthSky.

January charts Southern Hemisphere

White dots for Mercury and Venus in January for viewers in Southern Hemisphere. — For viewers in the Southern Hemisphere, Mercury will low in the southeast below Venus shortly before sunrise. Chart via John Jardine Goss/ EarthSky.

For precise sun and Mercury rising times at your location:

Old Farmer’s Almanac (U.S. and Canada)
timeanddate.com (worldwide)
Stellarium (online planetarium program)

Mercury events in 2023 and 2024

Note: Dates are listed based on UTC times

December 4, 2023: Greatest elongation (evening)
December 22, 2023: Inferior conjunction (races between Earth and sun)
Jan 12, 2024: Greatest elongation (morning)
Feb 28, 2024: Superior conjunction (passes behind sun from Earth)
Mar 24, 2024: Greatest elongation (evening)
Apr 11, 2024: Inferior conjunction (races between Earth and sun)
May 9, 2024: Greatest elongation (morning)
Jun 14, 2024: Superior conjunction (passes behind sun from Earth)
Jul 22, 2024: Greatest elongation (evening)
Aug 19, 2024: Inferior conjunction (races between Earth and sun)
Sep 5, 2024: Greatest elongation (morning)
Sep 30, 2024: Superior conjunction (passes behind sun from Earth)
Nov 16, 2024: Greatest elongation (evening)
Dec 5, 2024: Inferior conjunction (races between Earth and sun)
Dec 25, 2024: Greatest elongation (morning)

Mercury charts from Guy Ottewell

Sky chart with labeled constellations and objects, and positions of Mercury at elongations marked. — Mercury’s greatest morning elongations in 2024 – from the Northern Hemisphere – as viewed through a powerful telescope. The planet images are at the 1st, 11th and 21st of each month. Here, dots show the actual positions of the planet for every day. Chart via Guy Ottewell’s 2024 Astronomical Calendar. Used with permission.

Heliocentric solar system, December 2023 and January 2024

Circle with sun at center, planets around, and zodiac names on outer edge. — Heliocentric view of solar system, December 2023. Chart via Guy Ottewell’s 2024 Astronomical Calendar. Used with permission.

A comparison of elongations

Mercury’s greatest elongations are not created equal. Some are “greater” than others. For one thing, the distance of Mercury from the sun on our sky’s dome varies from about 28 degrees (maximum) to 18 degrees (minimum).

Also, Mercury elongations are better or worse depending on the time of the year they occur and your location on Earth. For both hemispheres, spring evenings and autumn mornings are best.

The chart below – from a Northern Hemisphere perspective – might help you visualize these differences.

Chart with row of steep, alternating light blue and gray arcs, each with a date and height in degrees. — Mercury elongations compared. Here, gray areas represent evening apparitions (eastward elongation). Blue areas represent morning apparitions (westward elongation). The top figures are the maximum elongations, reached at the top dates shown beneath. Curves show the altitude of the planet above the horizon at sunrise or sunset, for latitude 40 degrees north (thick line) and 35 degrees south (thin line). Maxima are reached at the parenthesized dates below (40 degrees north bold). Chart via Guy Ottewell’s 2024 Astronomical Calendar. Used with permission.

Seasons make a difference

So, in the autumn for either hemisphere, the ecliptic – or path of the sun, moon and planets – makes a narrow angle to the horizon in the evening. Conversely, it makes a steep slant, nearly perpendicular, in the morning. So – in autumn from either hemisphere – morning elongations of Mercury are best. Then, Mercury appears higher above the horizon and farther from the glow of the sun. Evening elongations in autumn are, however, harder to see.

On the other hand, in the spring for either hemisphere, the situation reverses. The ecliptic and the horizon meet at a sharper angle on spring evenings and at a narrower angle on spring mornings. So, in springtime for either hemisphere, evening elongations of Mercury are best. Meanwhile, morning elongations in springtime are harder to see.

Bottom line: Mercury reaches its greatest elongation – greatest distance from the sunrise – on January 12, 2024. Look east at dawn. It’ll brighten through early February before disappearing from the morning sky.

Posted

December 27, 2023

Astronomy Essentials

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