As we head deeper into spring, you can’t help but notice that as evening begins you can easily see the Big Dipper standing on its handle and pouring its celestial contents on Earth.
Weather and astronomy lore claim that the tipping Big Dipper brings April showers and May flowers.
The Big Dipper is actually the backside and tail of Ursa Major, otherwise known as the Big Bear. As you can see in the diagram, the Big Dipper is by far the brightest component of the Big Bear.
Ursa Major is one of the biggest constellations in the heavens, and you can use it to get your bearings. If you draw a line in your mind’s eye from the star Merak to the star Dubhe on the side of the Big Dipper’s pot opposite the handle, and then continue that line you’ll run right into Polaris, otherwise known as the North Star.
Clench your fist and hold it out at arm’s length. Three of those fist widths at arm’s length is about the distance you have to go from Dubhe to get to Polaris.
The North Star is what I like to call the lynch pin of the heavens. Since Polaris shines almost directly above the north pole, every celestial object appears to us to revolve around Polaris once every 24 hours in response to the Earth’s rotation.
The Big Dipper’s handle, or the tail of the Big Bear, can also be used as a pointer. In fact, the Big Bear’s tail is the first leg of what’s called the giant arc of spring, which goes well beyond Ursa Major and takes you to two of the brightest stars in the spring skies.
The middle star in the Big Dipper’s handle is a great eye test for you. That star is called Mizar, and if you look very carefully at Mizar with the naked eye, you’ll see that it has company. Just to the lower left of Mizar is a much fainter star, Alcor. Mizar and Alcor are what astronomers call an optical double.
Those are double stars that don’t have anything to do with each other physically but just happen to lie in the same line of sight from Earth. Mizar is 78.2 light-years away and Alcor is 81.2 light-years away. A light-year is the distance a beam of light travels in a year’s time in the vacuum of space, with one light-year equalling nearly 6 trillion miles.
There are many other fainter double stars that are gravitationally related to each other. In fact, more than half the stars we see appear to be single shiners but are actually systems of two, three or even more stars revolving around each other. A lone star like our sun is the exception rather than the rule.
If you continue along the arc of spring, beyond the arc of Big Bear’s handle, you’ll run right into Arcturus, a super bright star and in fact the second brightest nighttime star we see from around here.
Just remember the old stargazing saying, “arc to Arcturus.” Arcturus is the brightest star in the spring constellation of Bootes the Hunter Farmer. Bootes resembles a giant kite rising on its side in the eastern sky with Arcturus at the tail.
Arcturus is a bloated orange super giant star more than 25 times the diameter of sun. That would give it a girth of more than 20 million miles. Even with the naked eye you can easily see its orangish hue. It’s 37 light-years away, making it more than 214 trillion miles from your backyard.
If you continue the great arc of spring beyond Arcturus you’ll bump into the bright star Spica, in the large but faint constellation Virgo the Virgin. Spica isn’t as large as Arcturus, with a diameter of just under 5 million miles, but it’s a much hotter star. It kicks out 5,000 times more light than our sun.
Spica doesn’t shine as brightly as Arcturus because it is 263 light-years away. The light we see from Spica left that giant ball of glowing gas in 1749.
Mike Lynch is an astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis and is author of the book, “Washington Starwatch,” available at bookstores and at his Web site www.lynchandthestars.com.
The Everett Astronomical Society welcomes new members. Go to www.everettastro.org.
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