Sky ArchiveTonight

Find Mizar and Alcor in the Big Dipper

The second star to the end of the Big Dipper’s handle is called Mizar. Look closely, and you’ll see another fainter star, called Alcor, right next to it.

Tonight, find the Big Dipper, known as the Plough in the U.K. or, in Hindu astronomy, Saptarishi after the seven rishis. The chart at top shows the Big Dipper on an evening in March, ascending in the northeast during the evening hours. If you have a dark sky – and good vision – you might be able to see the faint star Alcor next to Mizar, the middle star in the Big Dipper’s Handle.

Mizar and Alcor are one of our sky’s most famous “visual double” stars.

The Big Dipper – minus the last star in the handle – as seen from Surabaya, East Java Indonesia. Mizar and Alcor are the 2 stars close together in the upper right corner of this 2017 photo by Martin Marthadinata.

Still not sure the pattern you’ve found is the Dipper? Check out the chart below.

The stars Dubhe and Merak are well known among amateur astronomers as The Pointers. If you extend a line about five times the distance between Dubhe and Merak from the star Dubhe – and don’t find a medium-bright star (Polaris) – then the pattern you see is not the Big Dipper. Keep looking.

From Northern Hemisphere locations, you should see the Big Dipper just off your northeast horizon around 9 p.m.

The two outer stars in the Bowl of the Big Dipper – Dubhe and Merak – always point to Polaris.

Mizar and Alcor served as an ancient eye tes. If you had lived in the time of the early Romans and could see Alcor, you would have been eligible to be an archer in the Roman army. If not, you likely would have served in another capacity for the Caesar.

It’s said that sultans of the past also tested their soldiers’ eyesight in this way.

At one time, astronomers doubted that Mizar and Alcor were gravitationally bound to one another. But Mizar is now thought to be four stars in one, and Alcor two stars in one. Given that Mizar and Alcor likely revolve around each other, that makes for six stars in an intricate gravitational dance.

Located in the handle of the Big Dipper, Mizar (brighter) and Alcor (fainter) are one of the most famous visual double stars in the sky. Image via ESO Online Digitized Sky Survey

Bottom line: As darkness falls, look for the Big Dipper and the star Mizar in the northeast sky. With either the unaided eye or binoculars, look for Mizar’s nearby companion: Alcor.

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March 7, 2017
Sky Archive

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