Mercury at greatest elongation, August 9-10, 2023

Bright Mercury and dim Mars are low in the west after sunset in August 2023. Can you pick them out in the bright twilight? It’s easier from Earth’s Southern Hemisphere. Look for them in the sunset direction, along the ecliptic – the path of the sun in our sky – shown as a green line on our chart. Look as soon as the sky begins to darken! Chart via John Jardine Goss/ EarthSky.

Mercury will reach its greatest elongation on August 9-10, 2023. It’ll be the best Mercury elongation of the year for the Southern Hemisphere.

Mercury in August 2023

Where to look: Look west, the sunset direction – shortly after sunset – for Mercury. The sun’s innermost planet should be easy to see, if you look west soon after sunset. Earth’s Southern Hemisphere has the best view.
Greatest elongation: Mercury is farthest from the sun – at greatest elongation – at 2 UTC on August 10, 2023 (9 p.m. CDT on August 9). It so happens Mercury reaches aphelion, its farthest point in orbit from the sun, on August 10, too. So, around August 9-10, Mercury is about as far from the sunset as it ever gets. It’s a whopping 27 degrees from the sun.
Brightness: Mercury began August 2023 already in the evening sky. And it has been bright so far, throughout early August. It’s been brighter than dim Mars, which is far across the solar system from Earth now, also in the west after sunset. At greatest elongation, Mercury shines at magnitude +0.3, making it brighter than most stars. But, after greatest elongation, the innermost planet will rapidly fade. It’ll probably disappear into the sunset glare around the 3rd week of August.
Through a telescope: Mercury will appear about 49% illuminated, at greatest elongation. It’ll measure 7.55 arcseconds across.
Constellation: Mercury will lie in front of the constellation Leo the Lion at this elongation. But most of stars of this constellation will be lost in the twilight.
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, your clock starts ticking. Will you see the glowing point of light that is Mercury before it drops below the horizon, following the setting sun?

Mercury elongation from the Southern Hemisphere

The August 2023 elongation of Mercury is the best of the year for Earth’s Southern Hemisphere. Why? The reason is the steep angle of the ecliptic (the green line on our chart), for Southern Hemisphere viewers, in August 2023. Contrast the angle of the ecliptic on this Southern Hemisphere chart to the angle of the Northern Hemisphere chart at the top of this post. 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

Note: Times are in UTC

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 August 2023

View larger. | Heliocentric view of solar system, August 2023. Chart via Guy Ottewell.

Overview of a Mercury 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 August 10, 2023. And it is 27 degrees from the sun in the evening sky. Chart via John Jardine Goss/ EarthSky.

A comparison of elongations

The farthest from the sun that Mercury can ever appear on the sky’s dome is about 28 degrees. And the least distance is around 18 degrees.

Also, elongations are better or worse depending on the time of year they occur. So in 2023, the Southern Hemisphere will have the best evening elongation of Mercury in August 2023. 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. That’s when Mercury appears higher above the horizon and farther from the glow of the sun. However, evening elongations in autumn are harder to see.

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.

View larger. | Mercury elongations compared. Here, gray areas represent evening apparitions (eastward elongation). And 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 2023 Astronomical Calendar. Used with permission.

More Mercury elongation comparisons for 2023

View larger. | Mercury’s greatest evening elongations in 2023 from the Northern Hemisphere as viewed through a powerful telescope. The planet images are at the 1st, 11th, and 21st of each month. Dots show the actual positions of the planet for every day. Chart via Guy Ottewell. Used with permission.

View larger. | Mercury’s greatest evening elongations in 2023 from the Southern Hemisphere as viewed through a powerful telescope. The planet images are at the 1st, 11th, and 21st of each month. Dots show the actual positions of the planet for every day. Chart via Guy Ottewell. Used with permission.

Mercury photos from our community

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!

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!

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!

Bottom line: Mercury is visible in the evening sky. Look in the west as the sky is darkening. The planet will reach its greatest elongation overnight on August 9-10, 2023.

Submit your photos to EarthSky here.

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

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