Ah, spring. Finally, it’s warm enough for even thin-blooded observers (like me) to break out their binoculars and telescopes. If you’re new to astronomy, however, you’ll want to become familiar with the constellations and bright stars that populate this season’s night sky before looking through the eyepiece. Then, when you read that a sky treat is in Boötes or near Regulus, you’ll already have a frame of reference.
High in the northeast, the sky’s most recognizable star pattern — the Big Dipper — is easy to spot after sunset. The Dipper is part of the third-largest constellation, Ursa Major the Great Bear, but the other stars are all faint, so concentrating on the Big Dipper is the way to start.
Find the bend of the Dipper’s handle. Sharp-eyed observers can tell that two stars occupy this space. Arabian astronomers 10 centuries ago called this pair the Horse and Rider. The brighter of the two is Mizar. It shines at magnitude 2.2. Alcor, which sits 0.2° east-northeast of Mizar, glows at magnitude 4. This pair is an optical double, as in optical illusion. Mizar lies 78.2 light-years away, while Alcor sits 81.2 light-years distant.
Because the Big Dipper is so easy to find, amateur astronomers use it to help them locate lots of constellations and stars in the spring sky. For example, use the Pointer Stars, Dubhe and Merak, to find perhaps the most famous single star in the sky: Polaris, the North Star. Draw a line from Beta through Alpha Ursae Majoris, and extend that line about five times the distance between those two stars.
Polaris, which lies roughly 430 light-years from Earth, marks the end of the Little Dipper’s handle. Alternatively, it’s the brightest star in Ursa Minor the Little Bear, and it marks the tip of the Bear’s tail. Unlike the Big Dipper, however, most of the other six stars of the Little Dipper are faint. You’ll need a dark location to see them all.
Head back to the Big Dipper, and locate its handle. Follow beyond the curve of the handle to two brilliant stars: Arcturus and Spica. These two luminaries illustrate some of the color differences between stars.
Arcturus appears copper-colored or orange, while Spica is bright blue. Stars have different colors because nuclear reactions in their cores heat their surfaces to different temperatures. Arcturus is a giant star with a relatively cool surface temperature of 4300 kelvins (7300° Fahrenheit). Spica also is a giant, but it’s among the hottest of stars. Its surface burns at 20,000 K (35,500° F). For comparison, the Sun lies in the middle of the temperature range. On its surface, a thermometer would read 6000 K (10,300° F).
Arcturus lies in the constellation Boötes the Herdsman some 37 light-years away. The star’s name comes from a combination of terms that means “the Bear’s guard,” which signifies its position near Ursa Major the Great Bear. The main part of Boötes looks like a thin kite or an ice-cream cone. Spica sits 260 light-years away in the southern reaches of Virgo the Maiden. This sprawling star group ranks second in size among the 88 constellations.
Go back to the Big Dipper. To find our next constellation, poke a hole in the Dipper’s bowl, let all the water run out, and wait for a loud roar. Mythologically, that’s what you’ll hear because the water fell on the back of Leo the Lion. Leo’s main figure has two parts: A backward question mark and a triangle. The question mark, or sickle-shaped figure, represents the front of the Lion. Dotting the question mark with a distinctive blue-white color is magnitude 1.3 Regulus. Regulus lies 77 light-years from Earth.
East of the sickle, a right triangle marks the Lion’s back and tail. The star farthest east of Regulus is Denebola. It lies 36 light-years away, about the same as Arcturus. Denebola marks the tip of Leo’s tail.
Some 20° west of Leo’s sickle lies one of the sky’s faintest constellations, Cancer the Crab. I identify this poor star pattern only so you can point binoculars toward its center. There you’ll find M44, the fabulous Beehive Cluster. Through 10×50 binoculars most observers can count three dozen stars. The Beehive Cluster lies at a distance of about 580 light-years.
Below Virgo sits the small constellation Corvus the Crow. Its four moderately bright main stars and “crooked box” shape make it easy to find. There’s another way to be sure you’re looking at Corvus: See if its top two stars point upward to Spica.
Spring is an ideal time to start learning the sky. Many of the constellations are large, and helpful indicators like the Big Dipper lead you to the brightest stars. Before you know it, summer will be here.
