Asterisms appeal to our playful side but also serve as key waypoints in the sky for identifying fainter stars and constellations.
Thank goodness for asterisms! If you're a beginning skywatcher, asterisms ease your entry into the night sky. Even seasoned observers know that most constellations don't look like the figures they're supposed to represent. OK, some do. Like Ursa Major, the Great Bear, or Delphinus, the Dolphin. But you'll pull your hair out trying to see a chained princess in Andromeda or the chariot-driving Auriga.
Asterisms are easy-to-recognize patterns that can be part of a larger constellation or composed of stars from more than one constellation. One of the biggest, the Winter Hexagon, borrows from six! Some asterisms even involve the entire constellation, as in the 'W' of Cassiopeia or the Northern Cross, a.k.a. Cygnus, the Swan.
All asterisms have one thing in common: they make wonderful places from which to begin learning the constellations.
A great many skywatchers have cut their teeth on Orion's Belt (yours truly) and the Big Dipper, straightforward, easy-to-recognize patterns of relatively bright stars. Finding the Belt is your passport to the rest of the great hunter.
From the Dipper, we can use the Pointer Stars (another asterism) to arrive at the North Star or explore the very bear-like outline of the constellation Ursa Major. While we're talking about the Belt, Aussie skywatchers, who see Orion upside-down from our northern perspective, picture a "saucepan" by combining the Belt with Orion's Sword. Since Orion is very much a summertime constellation viewed from down under, could homemade barbecue sauce be bubbling away in there, I wonder?
The Sickle of Leo asterism works backwards and forwards, west to faint Cancer the Crab and the Beehive Cluster and east to the lion's tail. Shooting lines through the Great Square of Pegasus, a favorite fall asterism, plunges our gaze into the watery depths where we meet up with Piscis Austrinus, the Southern Fish, and the gargantuan Cetus, the Sea Monster.
For sentimental reasons, Orion's Belt will always be my favorite, but no pattern connects more bright stars and offers avenues to a greater diversity of constellations than the Winter Hexagon. First-time skywatchers are wowed by the Hexagon's sheer size . . . and its brilliance.
From Capella to Sirius, top to bottom, the figure spans 65°, or more than six fists at arm's length, and 45° in width (Procyon to Aldebaran). Here's the kicker: Not only does it vie for biggest asterism in the known universe, it contains 7 of the sky's 21 first magnitude or brighter stars: Sirius, Procyon, Pollux, Capella, Aldebaran, Rigel, and Betelgeuse.
A word about Pollux's neighbor Castor. At magnitude 1.6, it's officially a 2nd-magnitude star, but situated so close to the figure, it doesn't seem right to exclude it. If we graciously include Castor, the Hexagon morphs into a 7-sided Heptagon.
Betelgeuse, sadly left out of all the geometric merrymaking, comes into its own in the Heavenly G, completing the letter's inner lobe. Whatever form you prefer, the best time to view it is around 9 to 11 p.m. in mid-January as it stands high (and low) in the south-southeastern sky.
Start with the unmistakably brilliant Sirius at the lowest apex and work your way clockwise and up to Procyon in Canis Minor, the Gemini Twins, the neck-cracking Capella near the zenith, then down to Aldebaran, and farther to sparkling, white Rigel in Orion. Swirl your gaze around it a few times for the full effect.
Now, imagine if you're new to the sky how helpful this asterism will be. Using these 6 or 7 stars you can pilot to a half-dozen constellations or more. What a great way to learn the sky — establish a base of operations from which to make nightly forays into lesser known realms.
One final asterism of winter nights is far less showy but no less amazing — the Three Leaps of the Gazelle. You'll spot it springing alongside the Big Dipper in the northeastern sky from about 9 o'clock on.
This is an ancient Arabic star group composed of three sets of paired stars that resemble starry hoof prints in the sky. None of the pairs is especially bright, but the six stars are stand-outs because they form a striking repetitive pattern. All of them belong to Ursa Major.
Legend has it that the gazelle was startled by the lion as it drank from a pond (Coma Berenices) near the lion’s lair. It sprang up and leaped across the sky from east (left) to west, leaving impressions in muddy ground. Here’s the breakdown on the stars’ names, which refers to the first, second, and third leap respectively from east to west:
* First Leap — Alula Australis (Nu UMa) and Alula Borealis (Xi UMa)
* Second Leap — Tania Australis (Lambda UMa) and Tania Borealis (Mu UMa)
* Third Leap — Talitha (Iota UMa) and Kappa UMa
Lots of skywatchers like making their own asterisms. Amateur astronomer Greg Furtman of Webster, Wisconsin, sees a stone skipping on water in a long arc of stars beginning with the "throwing arm" of the Big Dipper's Handle and ending half a sky later in southern Ophiuchus. And anyone who's used a telescope or finderscope to star-hop to a favorite deep sky object creates one temporary asterism after another to navigate their way from point A to the target.
Let me guess. You've probably created a few asterisms of your own. If you have, we'd love to hear from you. Just share your pattern in the comments section. Asterisms — they're everywhere!