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Doorstep Astronomy: Moon and Antares Get Close

Doorstep Astronomy: Moon and Antares Get Close
The moon often visits the bright red star Antares in Scorpius. (Image credit: Starry Night Software)

In its 29.5-day-long journey around the Earth, the moonpasses in front of all of the planets but relatively few stars that are brightenough to be visible close to the moon. The two brightest stars are Regulus inLeo and Antares in Scorpius. Wednesday night, Sept. 23, the 5-day-old moon willbe close to Antares.

Antares is Greek for ?opposite Mars,? referring to its deepred color, resembling Mars. At? present Antares is close to minimum brightness,which also means that it is at its reddest.

The problem with this conjunction between the moon andAntares is that Antares is rapidly disappearing into the sunset, so that thetrick is to observe it before it gets too low in the sky.

Because the moon is moving from right to left across thesky as the Earth?s rotation carries the stars from left to right, the distancebetween the moon and Antares gets smaller the farther west you are in NorthAmerica. On the east coast, let?s say Boston, at 8 p.m. E.D.T., the moon andAntares are 3? 50? apart. On the west coast, in Seattle, at 8 p.m. P.D.T. ,they are only 2? 10? apart.

(Your fist on an outstretched arm measures about 10? ofsky.)

What happens further west, out over the Pacific Ocean? Themoon actually passes in front of Antares, in what is called an occultation.Such occultations of bright stars are relatively rare, and to see themstargazers must be at the right place at the right time. Often the moon passesjust above or just below a star, and often occultations happen on the ?wrong?side of the Earth.

A conjunction between the Moon and a bright star or planetis something which requires no optical aid. It can be enhanced with ordinarybinoculars, but these aren?t necessary. So, step outside Wednesday eveningaround 8 p.m. your local time and look to the southwest.

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Geoff Gaherty
Geoff Gaherty

Geoff Gaherty was's Night Sky columnist and in partnership with Starry Night software and a dedicated amateur astronomer who sought to share the wonders of the night sky with the world. Based in Canada, Geoff studied mathematics and physics at McGill University and earned a Ph.D. in anthropology from the University of Toronto, all while pursuing a passion for the night sky and serving as an astronomy communicator. He credited a partial solar eclipse observed in 1946 (at age 5) and his 1957 sighting of the Comet Arend-Roland as a teenager for sparking his interest in amateur astronomy. In 2008, Geoff won the Chant Medal from the Royal Astronomical Society of Canada, an award given to a Canadian amateur astronomer in recognition of their lifetime achievements. Sadly, Geoff passed away July 7, 2016 due to complications from a kidney transplant, but his legacy continues at Starry Night.