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What is a conjunction?

People get excited about conjunctions in astronomy, and they are often beautiful. EarthSky community member Tom Wildoner provides an illustration.

Example of a conjunction involving Venus and the Pleiades cluster.

Example of a conjunction involving Venus and the Pleiades cluster, via Tom Wildoner at LeisurelyScientist.com.

Article and photos re-printed with permission from LeisurelyScientist.com

[Editor’s Note: In August, 2016, there will be conjunctions between the moon and Venus on or around August 3, the moon and Mercury on or around August 4, and the moon and Jupiter on or around August 5. Jupiter and Mercury come closest together for the month on August 19, and then Venus and Jupiter stage a stunningly close conjunction on August 27.]

Conjunctions occur all the time, some spectacular, others routine. Most involve the moon. In astronomical terms, a conjunction involves the close approach of two or more solar system bodies or a close approach of a single solar system body with another object in the sky (like a star cluster or bright star).

It’s important to remember that these conjunctions are only from our perspective here on the planet Earth, the objects are never actually close together. An example is the conjunction depicted on this page, between the planet Venus and the Pleiades star cluster in the constellation Taurus. This conjunction took place on April 12, 2015.

The Pleiades actually lie about 440 light years behind Venus in the night sky, but from our perspective they appeared to be side-by-side.

The photo below was taken using a Canon 6D and 100mm lens, unguided and tripod mounted. There was a thin layer of clouds at the time the photo was taken, I think it adds a nice effect to the photo.

Photo taken by Tom Wildoner on April 12, 2015 of the conjunction of Venus and the Pleiades Star Cluster.

Look back at the illustration above, and then look at this real photo of an April 12, 2015 conjunction of Venus and the Pleiades star cluster. Photo via Tom Wildoner at LeisurelyScientist.com.

Bottom line: Illustrations of the astronomical term conjunction. Precisely speaking, in astronomy, a conjunction occurs when two sky objects have the same right ascension or the same ecliptic longitude, as observed from Earth.

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