Now that we’re well into May, as soon as darkness sets in, you can easily see the Big Dipper, a celestial marvel, upside-down in the high northern sky. It’s pouring its celestial magic on us. According to old-time lore, the overturned Dipper is one of the reasons we get so much rain this time of year. That and some tender loving care will keep lawns green, gardens growing, and farm fields productive, along with helping maintain weeds, dandelions, and the livelihood of mosquitoes!
At my stargazing programs and parties, I always ask the folks how many constellations they can find in the sky. Most can point out two or three, but almost everyone can locate the Big Dipper, a starry friend who’s always there for us. Actually, it’s not a constellation but rather what astronomers call an asterism, which is defined as an easily recognized pattern of stars in the sky. It is not one of the “official” 88 constellations that can be seen from Earth, as agreed on internationally back in 1930.
(Mike Lynch)
The Big Dipper makes up the rear and the tail of the constellation Ursa Major, or the Big Bear. The four stars that outline the pot section of the Big Dipper also outline the bear’s derriere. The three stars of the handle outline the bear’s stretched-out tail. How it got stretched out is a story for another day. The rest of the stars (see diagram) that make up the head and legs of the Big Bear aren’t nearly as bright but can be spotted relatively easily this time of year, even in areas of moderate light pollution.
Just as the official constellations have mythology and lore associated with them, so does the Big Dipper. It can be argued that it’s as American as apple pie. Before the Europeans settled in America, the stars we know as the Big Dipper weren’t called the Big Dipper. In England, the Big Dipper was known as the Plough. In Germany, those stars were called “Charles’ Wagon”; in Ireland, “King David’s Chariot”; and in ancient Egypt, “The Leg of the Bull.” Several Native American tribes pictured the bowl of the Big Dipper as a giant bear. They imagined the three handle stars as a family chasing the bear, with the father leading the charge, followed by Mom with a frying pan and one of the kids tagging along in the rear.
No one knows for sure how the Big Dipper got its name in America, but there’s reason to believe that enslaved African-Americans before the Civil War in the 19th century had a lot to do with it. They drank from dippers made from hollowed gourds. The enslaved people pictured a bright giant gourd in the northern stars and referred to it as “The Drinking Gourd.” They associated it with freedom because it’s always in the northern sky, in the direction of where they could experience freedom. Enslaved people who managed to escape followed that drinking gourd northward to a new life. Eventually, the gourd evolved to the present-day moniker, The Big Dipper.
Constellations or asterisms in the night sky are mainly just an accidental scattering of stars that appear in the same general direction of space. Physically, the stars have nothing to do with each other. One big exception is the Big Dipper. Five of the seven stars in that constellation are believed to have formed together in the same nebulae. They began their stellar life about 200 million years ago as a small cluster that’s been breaking apart ever since. More than 30 other stars in the sky also used to be part of this same cluster. Dubhe and Alkaid are not part of the cluster, but the rest of the stars in the Big Dipper are. All of these stars are about 80 light-years away, give or take.
There’s a wonderful natural eye test in the Big Dipper, in the form of double stars Mizar and Alcor in the middle of the handle. Mizar is a bright star, but Alcor is much dimmer. If you can see Alcor, your long-range vision is in great shape; if you can’t, maybe it’s time to visit the eye doctor.
Alcor and Mizar are sometimes called the horse and rider, with the brighter star Mizar playing the part of the horse and dimmer Alcor as the rider. Looks can be deceiving, though.
These two stars are known astronomically as optical double stars. That is, they have no physical relation; they happen to be in the same line of sight. Mizar is 78 light-years away, and Alcor is nearly 82 light-years distant. By the way, just one light year equals about 6 trillion miles.
Take a look at Alcor and Mizar with even a small telescope, though, and you’ll see that Mizar is a double-star system. But high-tech astronomical analysis reveals that Alcor has an invisible companion star to the naked eye and that the two stars are a binary system, slowly orbiting each other. Get this, though: Astronomers have also discovered in the last year that Mizar is more than just a binary system. It’s actually a quintuple-star system with five stars in a highly complex orbit around each other.
Forget about Mizar and Alcor being the horse and rider, but five horses being driven by a pair of riders!
Mike Lynch is an amateur astronomer and retired broadcast meteorologist for WCCO Radio in Minneapolis/St. Paul. He is the author of “Stars: a Month by Month Tour of the Constellations,” published by Adventure Publications and available at bookstores and adventurepublications.net. Mike is available for private star parties. You can contact him at mikewlynch@comcast.net.
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