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
Venus after sunset in 2023 Southern Hemisphere
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.
Mercury before sunrise in 2023 Northern Hemisphere
Mercury before sunrise in 2023 Southern Hemisphere
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.
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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