Courtesy of EarthSky
A Clear Voice for Science
Look back to “this chart” for more about how to recognize the Big and Little Dippers on these almost-spring evenings.
The ancient eye test for those wishing to join the Roman army was administered using stars in the handle of our modern-day Big Dipper. If you passed, you got a job as an archer. If you failed, you had to serve in another capacity … perhaps as a cook. It is said that sultans of the past also tested their soldiers’ eyesight in this way.
You can take this ancient eye test, too. Go outside around 9 p.m. You should see the Big Dipper just off the northeast horizon. The middle star in the “tail” of the question mark is Mizar. If you look for a couple seconds longer, you may see a little starry point right next to Mizar. This star is called Alcor. If you had lived in the time of the early Romans, and you had seen Alcor, you would have been eligible to be an archer in the Roman army. If not, you would have to have served as cook or in another capacity for the Caesar.
“Mizar and Alcor” are what is called a “visual double star. There are three light-years difference between Mizar (78 light years away) and Alcor (81 light years away). If correct, this three light-year difference makes it unlikely that Mizar and Alcor are gravitationally bound to each other. However, Mizar is a true multiple star. It has several companion stars that are gravitationally bound to it and revolve around it.
Written by Earthsky