Astronomy Essentials

Mercury is up before sunrise and visible until mid-June

Mercury (close to horizon) and Jupiter (higher) as white dots along a green ecliptic line in dawn light.
Shortly before sunrise on May 29, 2023, Mercury will reach greatest distance from the sun and will lie very low in the east for viewers in the Northern Hemisphere. To its upper right shines the brighter planet Jupiter. Since Mercury stays close to the horizon in this apparition, it’ll be difficult to see in the Northern Hemisphere morning twilight. But this is a great time to look for both Mercury and Jupiter from Earth’s Southern Hemisphere. Chart via John Jardine Goss/ EarthSky.

On May 1, 2023, Mercury passed very close to the sun. In fact, if its inferior conjunction was about a week later, it would transit the sun. Even though a transit didn’t happen, Mercury was headed for its greatest morning elongation on May 29, 2023. This elongation is best viewed from the Southern Hemisphere where it rises about two hours before sunrise and will be visible until around mid-June.

At greatest elongation in May 2023

When to watch: Mercury became visible in mid-May 2023. It’s especially easy to find if you’re in the Southern Hemisphere, where the ecliptic (the green line on our charts) makes a steep angle with the eastern predawn horizon. Greatest elongation – when Mercury will be farthest from the sunrise on our sky’s dome – will be May 29. But the planet will continue getting brighter after that. So, in early June, although it’ll be edging back toward the sunrise, Mercury will be easier to spot in the morning twilight.
Where to look: Look in the sunrise direction, as the sky is getting lighter.
Greatest elongation is on May 29 at 6 UTC (1 a.m. CDT). Mercury will be shining at +0.6 magnitude that morning. And it’ll be 24.9 degrees from the sun.
Through a telescope on and around May 29, Mercury will appear 38% illuminated, in a crescent phase, and 8.2 arcseconds across. By the way, in mid-June it’ll be almost 75% illuminated by the time it slips out of view for Southern Hemisphere observers.
Note: Once you spot it, notice that Mercury brightens quickly in June, reaching around -1.0 magnitude before slipping away in the morning glare in mid-June.

Mercury in Southern Hemisphere in May 2023

Mercury and Jupiter as white dots along a green ecliptic line in dawn light. Jupiter is higher.
Shortly before sunrise on May 29, 2023, Mercury will lie in the east-northeast for Southern Hemisphere viewers. Above it, the brighter planet Jupiter will be shining. This apparition is better viewed from the Southern Hemisphere. Mercury will continue to brighten until it disappears from view in mid-June. Chart via John Jardine Goss/ EarthSky.

June 15 and 16 mornings: Moon near Mercury

Green ecliptic line with dots for Mercury and Jupiter with 2 very thin crescent moons.
The thin waning crescent moon, complete with earthshine, will lie close to Mercury on the mornings of June 15 and 16, 2023. The bright planet Jupiter will be higher in the morning sky. 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

January 7, 2023: Inferior conjunction (races between Earth and sun)
January 30, 2023: Greatest elongation (morning)
March 17, 2023: Superior conjunction (passes behind sun from Earth)
April 11, 2023: Greatest elongation (evening)
May 1, 2023: Inferior conjunction (races between Earth and sun)
May 29, 2023: Greatest elongation (morning)
July 1, 2023: Superior conjunction (passes behind sun from Earth)
August 10, 2023: Greatest elongation (evening)
September 6, 2023: Inferior conjunction (races between Earth and sun)
September 22, 2023: Greatest elongation (morning)
October 20, 2023: Superior conjunction (passes behind sun from Earth)
December 4, 2023: Greatest elongation (evening)
December 22, 2023: Inferior conjunction (races between Earth and sun)

Sky chart with labeled constellations and objects, and positions of Mercury at elongations marked.
View larger. | Mercury’s greatest morning 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. Here, dots show the actual positions of the planet for every day. Chart via Guy Ottewell.
Sky chart with labeled constellations and objects, and rows of dots for elongations of Mercury.
View larger. | Mercury’s greatest morning 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. Here, dots show the actual positions of the planet for every day. Chart via Guy Ottewell.

Heliocentric view of Mercury May 2023

Circle with sun at center, planets around, and zodiac names on outer edge.
View larger. | Heliocentric view of solar system, May 2023. Chart via Guy Ottewell.

A comparison of elongations

Not all of Mercury’s greatest elongations, however, are created equal. In fact, some are greater than others. That’s because the farthest from the sun that Mercury can ever appear on the sky’s dome is about 28 degrees. On the other hand, the least distance is around 18 degrees.

Also, elongations are better or worse depending on the time of year they occur and your location on Earth.

Chart with row of steep, alternating light blue and gray arcs, each with a date and height in degrees.
View larger. | 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). Maxima are reached at the parenthesized dates below (40 degrees north bold). Chart via Guy Ottewell’s 2023 Astronomical Calendar.

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. On the other hand, however, evening elongations in autumn are harder to see.

On the other hand, 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.

Diagram with orbits of Earth and an inner planet, showing relationship between them and the sun.
Greatest elongation represents the best time for stargazers to view the inner planets, Mercury and Venus. Illustration via John Jardine Goss/ EarthSky.

Bottom line: Watch for Mercury in the east before sunup around mid-May 2023. Mercury reaches greatest elongation – its greatest distance from the sunrise – on May 29 and then brightens through mid-June. It’s best viewed from the Southern Hemisphere.

Posted 
May 29, 2023
 in 
Astronomy Essentials

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