Learn the constellations
Constellations can help you sort the twinkling dots scattered across the night sky. Connect the stars to see what deep-sky wonders emerge.
If you're a newcomer to amateur astronomy, eager to begin exploring the night sky, you'll have to overcome one of astronomy's biggest hurdles — learning to identify the constellations. After all, you can't find the Andromeda Galaxy if you can't find Andromeda. Trying to make sense of those myriad stellar specks overhead might seem intimidating, but making friends with the stars needn't be a "mission impossible."
The richness of the summer sky is exemplified by the splendor of the Milky Way. Stretching from the northern horizon in Perseus, through the cross-shaped constellation Cygnus overhead, and down to Sagittarius in the south, the Milky Way is packed with riches. These riches include star clusters, nebulae, double stars, and variable stars.
Michel Hersen imaged the Milky Way from Stone Canyon, Utah, in June 2006.
Equipment used: Canon EOS Digital Rebel XT and Tamron 20-40mm wide-angle lens, ISO 1600, for a 90-second exposure
Photo by Michel Hersen
Remember your first day of school — entering that classroom and finding yourself confronted by a roomful of unfamiliar faces? Even on that first day, you probably made a few friends. Through them, and with your day-to-day exposure to the classroom, you gradually became acquainted with all of your classmates. Learning the constellations is like that. With a little help from your friends (easy-to-find guidepost constellations) and a willingness to "show up for class" on successive nights, you'll soon feel comfortable in your nighttime surroundings. So relax. It's time to go to school and meet some new friends!
|North circumpolar constellations|
We begin in the northern sky, realm of those always-visible star groups known as the north circumpolar constellations. The most prominent figure is the Big Dipper (Note: The Big Dipper is not a constellation). These bright stars — four forming the "bowl," three more tracing out the "handle" — create one of the most recognizable patterns in the night sky, an ideal guide for locating surrounding constellations.
As any good Boy or Girl Scout will attest, you can find Polaris, the North Star, by tracing a line between the stars Dubhe and Merak at the end of the bowl of the Big Dipper and extending it about five times the distance between them. When astronomical newcomers see this celebrated star for the first time, they are astonished that it isn't much brighter than the stars in the Big Dipper. Polaris is the brightest star in Ursa Minor the Little Bear, which contains the Little Dipper. Like its big brother, the Little Dipper is made up of seven stars — four in the bowl, and three in the handle. Because four of its stars are dim, the Little Dipper is hard to see in light-polluted skies.
If you trace a line from the bowl of the Big Dipper past the North Star and continue it an equal distance beyond, you'll arrive at an eye-catching group of stars that form a distinct letter M or W. This is Cassiopeia, Queen of Ethiopia
To see the constellations that come and go with the seasons, we need to turn our backs on the north circumpolar constellations and face south. If the winter sky seems alive with stars, it's no illusion. Besides the obvious facts that the air is clear and dry then, we're looking at a star-rich region that defines one of the spiral arms of our Milky Way Galaxy. Of the twenty-one brightest stars in the entire night sky (so-called 1st-magnitude stars), seven are in this area.
On a winter evening, the sky is home to what most astronomers agree is the grandest of all constellations — Orion the Hunter. A rectangle of bright stars, which includes, at opposite corners, 1st-magnitude Betelgeuse and Rigel, is bisected by a diagonal row of three bright stars (the "belt"). Beneath the belt hangs a row of three stars — Orion's "sword." Don't be fooled by their uninspiring naked-eye appearance; the middle star in the sword isn't a star at all.
This map shows the winter sky at 2 a.m. on December 1; midnight on January 1; and 10 p.m. on February 1.
Photo by Astronomy: Roen Kelly
It's the Orion Nebula — one of the grandest telescopic showpieces the night sky has to offer. In binoculars, it appears as a fuzzy patch of light. When you gaze at this wondrous glowing cloud, you view creation itself, for within this luminous glow, stars are being born.
Orion is the focal point of a stunning gathering of bright stars and constellations. The belt points down and to the left to a brilliant white star: Sirius, the brightest star in the night sky, leader of the constellation Canis Major the Great Dog. Sirius always dazzles, but the star especially captivates when positioned near the horizon. During winter, atmospheric refraction causes Sirius to sparkle in a rainbow of colors — a beautiful sight through binoculars or a small telescope.
Return to Orion's belt and continue up and to the right, and you arrive at a V-shaped group of stars called the Hyades. This is the "head" of Taurus the Bull. The reddish-orange 1st-magnitude star at the upper-left end of the V is Aldebaran — the eye of the Bull. Each end of the V extends outward to a star that forms one of the Bull's horns. Continuing past the Hyades, you'll see a little cluster of stars — one of the loveliest naked-eye sights in the night sky. This is the Seven Sisters, or Pleiades. Six are visible to the unaided eye under average sky conditions; binoculars reveal the seventh star, plus dozens more.
The uppermost horn of Taurus is part of a pentagon of stars that includes the bright golden-yellow star Capella. This pentagon is the constellation Auriga the Charioteer. Auriga lies above Orion and is overhead on a midwinter evening. The fact that these five stars represent a man on a chariot carrying a goat (Capella) attests to the vivid imagination of its ancient discoverers. Oh yes, that little triangle of stars beneath Capella represents the goat's three kids!
Orion's heavenly court includes Gemini the Twins. From Orion, extend a line upward from Rigel through Betelgeuse to this neat rectangular constellation, which contains the bright stars Pollux and Castor. In 2005, Gemini will be more aptly called the "Triplets," for Pollux and Castor will be joined by a third bright "star" — Saturn. Midway and slightly left of a line between Sirius and the stars Pollux and Castor is the 1st-magnitude star Procyon. Procyon forms an equilateral triangle with Betelgeuse and Sirius. It's about all you'll see of Canis Minor the Little Dog.
Winter constellation audio tours
As the days lengthen and the weather warms, Orion and his wintry retinue process slowly into the western sky. Leo the Lion now assumes center stage high in the south. Leo's most noticeable feature is an asterism (a grouping of stars) that reminds observers of a sickle or a backward question mark. The period on the question mark is the 1st-magnitude star Regulus. To the left of the Sickle are three stars that form a right triangle. We see the Lion from the side; the Sickle outlines his head, and the triangle, his hindquarters. Viewed with a little imagination, Leo definitely sports a feline profile.
During spring, the Big Dipper appears nearly overhead from mid-northern latitudes. If you follow the handle of the Dipper away from the bowl, you'll "arc to Arcturus," a golden-yellow 1st-magnitude star in the constellation Boötes the Herdsman. The constellation itself is shaped like a huge kite, with Arcturus at its base. Continuing the arc, you'll "sprint to Spica." This blue-white 1st-magnitude star is in Virgo, which is a huge, sprawling constellation.
1 a.m. on March 1; 11 p.m. on April 1; 9 p.m. on May 1. Add one hour for daylight-saving time.
Photo by Astronomy: Roen Kelly
If you look below and to the right of Spica, you'll spot a neat little group of four bright stars that resembles the outline of a sail. This is the constellation Corvus the Crow. I'm always impressed at how stately this little constellation looks, perched above the treetops to the south on a clear spring evening.
Spring constellation audio tours
Summer is a season of mixed blessings for astronomers. The nights are warm but short and often hazy. As if that weren't bad enough, we have to contend with swarms of blood-sucking mosquitoes! Haze and insects aside, the summer sky is a veritable gallery of cosmic masterpieces. The Milky Way arches high across the sky, which is richer than its winter counterpart because we now look toward the heart of our galaxy. Dominating the evening sky are three 1st-magnitude stars forming the Summer Triangle. Vega is the brightest of the three and is located in a nifty little constellation called Lyra the Lyre.
Our second Summer Triangle star, Deneb, is the tail of Cygnus the Swan. Deneb and four other bright stars of the Swan form an asterism called the Northern Cross, which is immersed in the Milky Way. Deneb is at the top of the cross, the star Albireo is at the base. Albireo is a double star famous for its rich colors of golden yellow and sapphire blue. The star pair can be split with binoculars, but the colors can be seen only through a telescope.
1 a.m. on June 1; 11 p.m. on July 1; 9 p.m. on August 1. Add one hour for daylight-saving time.
Photo by Astronomy: Roen Kelly
Farther south on the Milky Way is the bright star Altair and its parent constellation, Aquila the Eagle. If you follow the Milky Way from Aquila toward the southern horizon, you should find a group of stars that looks like a teapot. This asterism is part of Sagittarius the Archer. This constellation marks the location of our galaxy's center. The area teems with deep-sky treasures — especially bright nebulae and star clusters. To the right of the teapot is the ruddy 1st-magnitude star Antares, the "heart" of Scorpius the Scorpion. Like the winter star Betelgeuse, Antares is a red supergiant star in the last stages of its life. A fishhook-shaped row of stars trailing down and to the left of Antares forms the Scorpion's tail and stinger, while an upright row of three stars to Antares's right marks the location of its claws.
Summer constellation audio tours
As the nights begin to lengthen and a chill pervades the air, the summer Milky Way exits center stage (although the Summer Triangle remains visible in the west until early winter). Following the Summer Triangle is one of the night sky's prettiest constellations — Delphinus the Dolphin. Four stars, arranged like a diamond, form the Dolphin's head, while a fifth creates the tail. You can imagine a dolphin leaping out of the water as you gaze at this constellation.
In its wake is a rather barren expanse of sky whose most prominent feature is the Great Square of Pegasus the Winged Horse.
1 a.m. on September 1; 11 p.m. on October 1; 9 p.m. on November 1. Add one hour for daylight-saving time.
Photo by Astronomy: Roen Kelly
Alpheratz is at the top left corner of the Great Square. From here, two rows of stars branch out and up. This is the constellation Andromeda the Princess. And yes, it is home to the great Andromeda Galaxy. At a distance of 2.7 million light-years from Earth, it's the most remote object readily visible to the naked eye. Through binoculars, however, you'll see an elliptical glow (the galaxy's bright nucleus), which appears larger in small telescopes.
Now that I've introduced you to some of the constellations, it's time to head out and make your own friends. The expansive night sky will become more familiar to you after spending quality time learning the "faces" of the constellations. Class dismissed!
Autumn constellation audio tours
|Additional constellation observing tools from Astronomy magazine|
- Video: How to use a star chart — Senior Editor Rich Talcott helps you navigate the night sky using Astronomy magazine's pullout star chart, located in the center of each monthly issue.
- StarDome — Astronomy.com's interactive star chart lets you construct an accurate map of your sky and find your favorite constellations.
- Constellation observing — Downloadable articles that highlight all 88 constellations in the sky and explain how to observe each constellation's deep-sky targets.
- The starry sky — Learn a few constellations and you'll have a familiar friend every clear night.
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