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

Winter

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.

the winter sky

This map shows the winter sky at 2 a.m. on December 1; midnight on January 1; and 10 p.m. on February 1.

Astronomy: Roen Kelly

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. 

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.

Spring

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.

The spring sky

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.

Astronomy: Roen Kelly

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. 

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.


http://www.astronomy.com/observing/astro-for-kids/2008/03/learn-the-constellations