Astronomy Essentials

Mercury is up before sunrise: Start watching now

Mercury moves away from the sunrise direction on January 16 and comes back closer on January 30.
Little Mercury can be found very low before sunrise around January 16, 2023. It reaches its greatest angular distance from the sun, known as greatest elongation, on January 30. To be sure, this apparition of Mercury is better viewed from the Southern Hemisphere, but you might see it from anywhere on the globe. Moreover, binoculars may help find the elusive planet. Chart via John Jardine Goss/ EarthSky.

Mercury becomes visible for Southern Hemisphere observers near the sunrise point around mid- to late January 2023. Presently, it’ll be brightest before sunrise after it reaches greatest elongation, into the month of February.

At greatest elongation in January 2023

When to watch: Mid- to late January 2023 is a good time to look for Mercury! That is, it’s good if you’re in the Southern Hemisphere, where the ecliptic (the green line on our chart below) 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 January 30. But, the planet will continue getting brighter after that. So, by early in February, although it’ll be edging back toward the sunrise, Mercury will be easier to spot in the morning twilight.
Where to look: Accordingly, look in the sunrise direction, as the sky is getting lighter.
Greatest elongation is on January 30 at 6 UTC (12 a.m. CST). Mercury will be shining at -0.2 magnitude that morning.
Through a telescope on and around January 30, Mercury will appear as 63% illuminated, in a waxing gibbous phase, and 6.7 arcseconds across. By the way, it will be almost 90% illuminated by the time it slips out of view for Southern Hemisphere observers, in mid-to-late February.
Note: Once you spot it, notice that Mercury brightens quickly in late January and early February, reaching -0.1 magnitude on both sides of greatest elongation. Then, it will reach -1.1 magnitude before slipping away in the morning glare later in February.

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Mercury in Southern Hemisphere in January 2023

Mercury moves away from the sunrise direction on January 16 and comes back closer on January 30. Teapot on the right side of the line of ecliptic.
Little Mercury can be found low in the sky before sunrise around January 16. Later, it reaches its greatest angular distance from the sun, known as greatest elongation on January 30. It lies below the Teapot of Sagittarius the Archer. 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 constellations and objects labeled.
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 constellations and objects labeled.
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.

A comparison of elongations

Not all of Mercury’s greatest elongations, however, are created equal. In fact, some are greater than others. Generally speaking, 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 also better or worse depending on the time of year they occur and your location on Earth.

Chart with light blue and gray waves, black annotations, comparing Mercury elongations in 2023 and 2024.
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.

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.

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

Bottom line: Watch for Mercury in the east before sunup in January 2023. Mercury reaches greatest elongation – its greatest distance from the sunrise – on January 30 and remains bright through mid-February.

Posted 
January 25, 2023
 in 
Astronomy Essentials

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