A working knowledge of the night-time sky can enormously enrich one’s nocturnal hours and provide an exhilarating perspective on our very existence. Here is a basic guide to some of the more prominent celestial attractions.
The key grouping is the Big Dipper, an asterism of the constellation Ursa Major, the Great Bear. In Spring the dipper is upside down, above Polaris.
The two outside stars, now on the left, are the pointers. An imaginary line extended downward, five times the distance between the pointers, will bring you to Polaris, the famous North Star, and the tail star of the Little Dipper.
Polaris is very close to the north celestial pole and nearly in a direct line with the earth’s rotational axis. Therefore, it remains almost motionless while the rest of the stars and constellations slowly revolve around it, making a complete circuit every 24 hours.
The Dipper can locate other treasures:
Extend the curving handle outward and it will lead to the dazzling orange Arcturus, which is part of the constellation Bootes, an upside down, elongated diamond. Immediately to the right is the lovely Corona Borealis, the Northern Crown, a glittering curve of jewels.
By following the handle out beyond Arcturus you come to a blue giant, Spica, in the constellation Virgo.
If you reverse that line through the pointers and extend it upward you will come to a bright 1st magnitude star, Regulus, “Little King”, which is part of the constellation Leo, and lies on the ecliptic, the path that the sun and the planets travel as they make their way across the sky.
Below Polaris you might notice a stray letter of the alphabet. This is Cassiopeia, a somewhat flattened “W” (“M” in the Fall), actually a vain queen on her throne, who boasted of her flawless beauty. Cassiopeia and the Dipper remain opposite each other as they rotate around Polaris.
Facing south, to the right of Leo is Gemini, two long parallel lines topped by the twins Pollux and Castor.
Leo, Gemini and Virgo are all constellations of the Zodiac, an annual cycle of 12 zones along the aforementioned ecliptic. Some of them, like Cancer and Pisces, are faint and difficult to see.
Now the Big Dipper has swung around to the west of Polaris. Cassiopeia is higher and better placed for viewing. Straight up from the “Queen” is the white supergiant, Deneb,(Arabic for “”tail”) which forms the head of the well-known Northern Cross, itself an asterism of the constellation Cygnus, the Swan.
Looking south, it is easy to pick out the dominant feature of the summer sky, the so called Great Triangle, formed by Deneb, Vega and Altair. Each star has its attendant constellation.
Especially attractive is the tiny parallelogram Lyra, containing the luminous, blue-tinged Vega (Arabic, “falling wing”).
When Neolithic man was just starting the Agricultural revolution, around 12,000 BC, Vega was the Northern Pole Star, not Polaris, and will be again in another 12,000 tears.
Altair (Arabic, “the bird”), the third point of the Great Triangle, is part of Aquila, the Eagle. It is notable for its proximity to earth (17 light years) and its rapid rotation- 61/2 hours, vs. 25 days for the sun.
In mid-summer the Milky Way, the glorious center of our galaxy, winds its way right along the axis of the Northern Cross; on a balmy evening you are invited to stretch out on the grass with your lemonade (or martini), and wander through a vast array of literally hundreds of millions of stars, nebulae and clusters.
The farther south your latitude the more easily you will be able to view the impressive sight of Scorpius, one of the most stunning sights in the heavens. The curving tail of the scorpion, sent by the goddess Hera, is poised to strike the hunter Orion, who ironically is out of sight in another part of the sky. Near the top of Scorpius is Antares, a massive red supergiant, 700 times the diameter of the sun.
The Dipper is south of Polaris, not far above the horizon. In ages past, as the leaves began to change color and the night air became crisp, Native American mothers would tell their children that the Great Bear was searching for a place to lie down and sleep for the approaching winter, and that is why it was so low in the sky.
Now Cassiopeia has changed form a “W” to an “M”.
There is a twinkling little cluster of stars towards the northeast that has intrigued cultures since antiquity-the Pleiades, the Seven Sisters of Greek mythology.
There are actually about a thousand objects in the cluster, mainly hot blue stars, but if you can pick out the brightest seven your visual acuity is excellent.
Facing south of the Milky Way is like gazing through a window out of our galaxy. Due south of Cassiopeia is the Andromeda Galaxy (M31). If you look directly overhead, around 9PM, a 4th magnitude smudge of light passes directly overhead in mid-November, near the big square of the constellation Pegasus. When you gaze at this hazy patch you are looking at one of the farthest objects it is possible to see with the naked eye-2.2 million light years away!
It is a spiral galaxy, part of the Local Group that includes our own Milky Way, and contains some 200 billion stars. Unlike most galaxies it is moving toward us and is therefore blue shifted.
The combination of a cold clear atmosphere and an unusually rich array of first magnitude stars make the winter sky an extraordinary experience for stargazers.
Our friend the Big Dipper is now standing on his tail. Leo is doing likewise to the east. But the “superstar” of the winter sky has to go to mighty Orion the hunter. It consists of four outer bright stars and a slanting “belt” of three stars in the middle.
Like the Dipper, Orion is a useful “locator” constellation. Extending the line of the Belt downward you come to Sirius, the Dog Star, as it is part of Canis Major (Big dog), the brightest star in the sky, both because of its intrinsic brightness and proximity to earth. Its rising coincided with the annual flooding of the Nile, duly noted by ancient Egyptians.
Extend the line upward through the Belt and you come to Aldeberan, (Arabic, “the follower”), the orange bull’s eye in the constellation Taurus, a thin open triangle of stars.
Betelgeuse is the top left star, on Orion’s shoulder. This red supergiant is one of the largest stars known. Rigel, in the bottom right corner, is another supergiant and shines with 40,000 times the luminosity of the sun. It is in fact the most luminous star in our region.
Below the three stars of Orion’s belt is the dagger where the Great Nebula, M42 resides. Unlike the Andromeda Galaxy this is a gaseous cloud, illuminated by the heat of nearby stars. Mythologically speaking, this is the dagger with which Orion is about to attack Taurus, the nearby bull.
A lot going on up there.
A pair of binoculars will allow you to pick out much more details-exotically colored stars and nebulae, double stars and clusters, and the moons of various planets. Reading up on terms like celestial mechanics, spectral classes and galaxy structures will reveal even more mysterious secrets. And for sheer thrills, make a trip to a major observatory and peer at the rings of Saturn through a lens that might be 30 feet across!
Soon you will be looking up at a sky full of old friends, because you will have learned to read the celestial map of the night.