At superior conjunction, Venus or Mercury are behind the sun from Earth. At inferior conjunction, Venus or Mercury are between the Earth and sun. At greatest elongation, Venus or Mercury are most to one side of the sun. Around greatest elongation, these inner planets, Mercury and Venus, are at their greatest distances from the sun on our sky’s dome. Illustration via John Jardine Goss.
In 2023, Venus will reach greatest elongation at 11 UTC on June 4.
What is an elongation?
Astronomers use the word elongation to describe the angular distance – the distance on the sky’s dome – between the sun and one of the inner planets in our solar system, Mercury or Venus. Elongations are measured in degrees eastward or westward of the sun. Greatest elongations signal the best time to observe one of the inner planets. At greatest elongation, Venus or Mercury are typically farthest from the sun’s glare.
At greatest eastern elongation, Mercury or Venus are visible as an evening object that sets in the west after the sun.
At greatest western elongation, Mercury or Venus are visible as a morning object that rises in the east before the sun.
Maximum distance of Mercury from the sun at greatest elongation = 28 degrees.
Minimum distance of Mercury from the sun at greatest elongation = 18 degrees.
Maximum distance of Venus from the sun at greatest elongation = 47 degrees.
Minimum distance of Venus from the sun at greatest elongation = 45 degrees.
What is superior conjunction? And inferior conjunction?
Look again at the diagram at the top of this page.
At superior conjunction, Venus or Mercury are behind the sun from Earth.
At inferior conjunction, Venus or Mercury are between the Earth and sun.
Venus after sunset in 2023 Northern Hemisphere
View larger. | Venus’ evening elongation in 2023 from the Northern Hemisphere as viewed through a powerful telescope. Greatest elongation will come on June 4. The planet images are shown on the 1st, 11th, and 21st of each month. Dots show the actual positions of Venus every day. Chart via Guy Ottewell’s 2023 Astronomical Calendar. Used with permission.
Venus after sunset in 2023 Southern Hemisphere
View larger. | Venus’ evening elongation in 2023 from the Southern Hemisphere as viewed through a powerful telescope. Greatest elongation will come on June 4. The planet images are at the 1st, 11th, and 21st of each month. Dots show the actual positions of Venus every day. Chart via Guy Ottewell’s 2023 Astronomical Calendar. Used with permission.
Elongation comparison for Venus
Not all of Venus’ greatest elongations are created equal. That’s because the farthest from the sun that Venus can ever appear on the sky’s dome is about 47.3 degrees. On the other hand, the least distance is around 45.4 degrees.
Elongations are also higher or lower depending on the time of year they occur and your location on Earth.
View larger. | A comparison chart of Venus elongations in 2023. 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. Used with permission.
Mercury before sunrise in 2023 Northern Hemisphere
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. Used with permission.
Mercury before sunrise in 2023 Southern Hemisphere
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. Used with permission.
Elongation comparison for Mercury
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.
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. Used with permission.
Bottom line: Greatest elongations of Mercury and Venus are the best times to observe these inner worlds, in either the morning or evening sky.
Kelly Kizer Whitt has been a science writer specializing in astronomy for more than two decades. She began her career at Astronomy Magazine, and she has made regular contributions to AstronomyToday and the Sierra Club, among other outlets. Her children’s picture book, Solar System Forecast, was published in 2012. She has also written a young adult dystopian novel titled A Different Sky. When she is not reading or writing about astronomy and staring up at the stars, she enjoys traveling to the national parks, creating crossword puzzles, running, tennis, and paddleboarding. Kelly lives in Wisconsin.
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