Sky Maps Help

By — McGraw-Hill Professional
Updated on Sep 15, 2011

Introduction to Stars and Constellations—Illusions and Myths

We may never know exactly what the common people of ancient times believed about the stars. We can read the translations of the works of the scribes, but what about the shepherds, the nomads, and the people in the ages before writing existed? They must have noticed that stars come in a variety of brightnesses and colors. Even though the stars seem to be scattered randomly (unless the observer knows that the Milky Way is a vast congregation of stars), identifiable star groups exist. These star groups do not change within their small regions of the sky, although the vault of the heavens gropes slowly westward night by night, completing a full circle every year. These star groups and the small regions of the sky they occupy are called constellations .

Illusions And Myths

We know that the constellations are not true groups of stars but only appear that way from our Solar System. The stars within a constellation are at greatly varying distances. Two stars that look like they are next to each other really may be light-years apart (a light-year is the distance light travels in a year) but nearly along the same line of sight. As seen from some other star in this part of the galaxy, those two stars may appear far from each other in the sky, maybe even at celestial antipodes (points 180 degrees apart on the celestial sphere). Familiar constellations such as Orion and Hercules are their true selves only with respect to observers near our Sun. Interstellar travelers cannot use the constellations for navigation.

Cosmic Circus

Many of the constellations are named for ancient Greek gods or for people, animals, or objects that had special associations with the gods. Cassiopeia is the mother of Andromeda. Orion is a hunter; Hercules is a warrior; Draco is a dragon. There are a couple of bears and a couple of dogs. There is a sea monster, most likely a crazed whale, who almost had Andromeda for supper one day. There is a winged horse, a pair of fish whose tails are attached, a bull, a set of scales used to mete out cosmic justice, a goat, twin brothers who look after ocean-going vessels, and someone pouring water from a jug that never goes empty. The Greeks saw a lot of supernatural activity going on in the sky. They must have thought themselves fortunate that they were far enough away from this lively circus so as not to be kept awake at night by all the growling, barking, shouting, and whinnying. (If the ancient Greeks knew what really happens in the universe, they would find the shenanigans of their gods and animals boring in comparison.)

The people of Athens during the age of Pericles saw the exact same constellations that we see today. You can look up in the winter sky and recognize Orion immediately, just as Pericles himself must have. The constellations, as you know them, will retain their characteristic shapes for the rest of your life and for the lives of your children, grandchildren, and great-grandchildren. In fact, the constellations have the same shapes as they did during the Middle Ages, during the height of the Roman Empire, and at the dawn of civilization, when humans first began to write down descriptions of them. The positions of the constellations shift in the sky from night to night because Earth revolves around the Sun. They also change position slightly from century to century because Earth’s axis slowly wobbles, as if our planet were a gigantic, slightly unstable spinning top. But the essential shapes of the constellations take millions of years to change.

By the time Orion no longer resembles a hunter but instead perhaps a hunched old man or a creature not resembling a human at all, this planet likely will be populated by beings who look back in time at us as we look back at the dinosaurs. As life on Earth evolves and changes shape, and as the beings on our planet find new ways to pass through life, so shall the mythical deities of the sky undergo transformations. Perhaps Orion will become his own prey, and Draco will be feeding Hercules his supper every evening.

Sky Maps

In this chapter, the general shapes of the better-known constellations are shown. To see where these constellations are in the sky from your location this evening, go to the Weather Underground Web site at the following URL:

Type in your ZIP code or the name of your town and state (if in the United States) or your town and country and then, when the weather data page for your town comes up, click on the “Astronomy” link. There you will find a detailed map of the entire sky as it appears from your location at the time of viewing, assuming that your computer clock is set correctly and data are input for the correct time zone.

Celestron International publishes a CD-ROM called The Sky , which shows stars, planets, constellations, coordinates, and other data for any location on Earth’s surface at any time of the day or night. This CD-ROM can be obtained at hobby stores that sell Celestron telescopes.

Practice problems of this concept can be found at: Stars and Constellations Practice Problems

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