Tonight

Mercury after sunset: Greatest elongation December 21

Constellations at twilight withi Mercury and Venus.
Sunset view on December 21, 2022, with Mercury and Venus visible near the horizon. By the way, you can start looking for Mercury and Venus after the sun sets below the horizon. Mercury reaches greatest elongation from the sun that day. Chart via stellarium.org. Used with permission.

Mercury is having its fourth evening apparition for 2022. Wow! In fact, start looking for Mercury in the evening sky the second week of December. It will reach greatest elongation on December 21, 2022. As a bonus, Mercury will be 5 degrees away from dazzling Venus that evening.

Where to look: Look for Mercury in the sunset direction, as soon as the sky begins to darken. Try sweeping for Mercury with binoculars. It might surprise you, and pop into view.
When to look: Mercury begins this evening apparition around December 7. It’ll disappear again at the end of the month.
Greatest elongation: Is at 15 UTC on December 21, 2022. At greatest elongation, Mercury is farthest from the sunset for this evening apparition, and 20 degrees from the sun in the evening sky.
Brightness at greatest elongation: Mercury shines at magnitude -0.6.
Through a telescope: Mercury appears about 60% illuminated, in a waxing gibbous phase, 6.8 arcseconds across.
Elongation constellation: Venus is in the constellation of Sagittarius the Archer.
Note: As the innermost planet, Mercury is tied to the sun in our sky. As a result, it never ventures very far above the horizon after sunset. So, as soon as the sun disappears below your horizon, the clock starts ticking. Will you see the glowing point of light that is Mercury before it follows the setting sun?

For precise views from your location, we recommend stellarium.org.

The view from the Northern Hemisphere

Mercury and Venus December 2022
Mercury and Venus from the Northern Hemisphere. Mercury is at greatest distance from the sun on December 21, 2022. Plus, brilliant Venus is 5 degrees from Mercury that day. Chart via John Jardine Goss / EarthSky.

The view from the Southern Hemisphere

Mercury and Venus, Southern Hemisphere, December 2022
Mercury and Venus from the Southern Hemisphere. Mercury is at greatest distance from the sun on December 21, 2022. And brilliant Venus is 5 degrees from Mercury that day. 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 2022 and 2023

Dec 21, 2022: Greatest elongation (evening)
Jan 7, 2023: Inferior conjunction (races between Earth and sun)
Jan 30, 2023: Greatest elongation (morning)
Mar 17, 2023: Superior conjunction (passes behind sun from Earth)
Apr 11, 2023: Greatest elongation (evening)
May 1, 2023: Inferior conjunction (races between Earth and sun)
May 29, 2023: Greatest elongation (morning)
Jul 1, 2023: Superior conjunction (passes behind sun from Earth)
Aug 10, 2023: Greatest elongation (evening)
Sep 6, 2023: Inferior conjunction (races between Earth and sun)
Sep 22, 2023: Greatest elongation (morning)
Oct 20, 2023: Superior conjunction (passes behind sun from Earth)
Dec 4, 2023: Greatest elongation (evening)
Dec 22, 2023: Inferior conjunction (races between Earth and sun)

Heliocentric view of Mercury December 2022

Circle with sun at center, planets around, and zodiac names on outer edge.
View larger. | Heliocentric view of solar system, December 2022. Chart via Guy Ottewell.

A comparison of elongations

As a matter of fact, not all of Mercury’s greatest elongations are created equal. Indeed, some are greater than others. Ultimately, the farthest from the sun that Mercury can ever appear on the sky’s dome is about 28 degrees. And the least distance, comparatively, is around 18 degrees.

Also, elongations are better or worse depending on the time of year they occur. In 2022, the Southern Hemisphere had the best evening elongation of Mercury in August. And the Northern Hemisphere had the best evening apparition in April.

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. But 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. However, evening elongations in autumn are harder to see.

But, in the spring for either hemisphere, the situation reverses. The ecliptic and horizon meet at a sharper angle on spring evenings and 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.

Chart with light blue and gray waves, black annotations, comparing Mercury elongations in 2022.
View larger. | Mercury elongations compared. 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). Maxima are reached at the parenthesized dates below (40 degrees north bold). Chart via Guy Ottewell’s 2022 Astronomical Calendar.

The December Mercury elongation is decent for both hemispheres

Yet for this December elongation of Mercury, neither hemisphere is really favored for viewing the elusive planet. Overall, it’s a decent apparition for both hemispheres.

2022 December Mercury Greatest Elongation
At greatest elongation, Mercury is on one side of the sun and is at its greatest distance from the sun on our sky’s dome. Mercury reaches greatest elongation from the sun on December 21, 2022, at 15 UTC. And is 20 degrees from the sun in the evening sky. Chart via John Jardine Goss / EarthSky.

Photos from our community

Crescent moon, 2 labeled dots in blue and orange sky over a lighted suspension bridge.
View at EarthSky Community Photos. | Alexander Krivenyshev of the website WorldTimeZone.com captured this photo of the moon together with Mercury and Venus on May 13, 2021, from Newport, Rhode Island. Thank you, Alexander!
Sunset with trees and label of Mercury on small dot.
View at EarthSky Community Photos. | Joel Weatherly in Edmonton, Alberta, Canada, took this image on April 23, 2022. Joel wrote: “While the early morning planetary alignment garners attention, lonely little Mercury is making an appearance in our evening skies. Despite being elusive, it was easy to see without optical aid once sighted. Mercury will remain a pleasant addition to our evening skies as it reaches its greatest eastern elongation on April 29.” Thank you, Joel!
Lifeguard tower in the foreground, crescent moon and Mercury in a twilight sky.
View at EarthSky Community Photos. | Chix RC captured this image on January 3, 2022, from Hermosa Beach, California. See Mercury to the upper right of the crescent? Chix wrote: “A faint young moon at 1% illumination and Mercury.” Thank you, Chix!
Mercury and Mars close together in dim sunset sky over wooded hills.
Peter Lowenstein of Mutare, Zimbabwe, caught Mercury and Mars in the evening twilight on August 18, 2021. Thank you, Peter!

Submit your photos to EarthSky here.

Some resources to enjoy

Read about greatest elongations, superior and inferior conjunctions: Definitions for stargazers

Bottom line: Mercury is currently visible during its evening apparition. So look in the sunset direction, as the sky is darkening. The planet reaches greatest elongation on December 21, 2022. By the way, bright Venus is visible as well.

Posted 
December 21, 2022
 in 
Tonight

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