Astronomy 101: The Constellations

Constellations, asterisms, and their names. Carolyn Collins Petersen

Observing the night sky is one of the oldest pastimes in human cultures. It likely goes back to the earliest human ancestors who began to use the sky for navigation and a calendar.

If you're an early hominid with some free time at night, what do you do to amuse yourself? What do you fill your free time with when movies, television, and even radio haven’t been invented, and won’t be for hundreds, or even thousands of years?

That's the issue our ancient ancestors faced. They told stories, performed plays, wrote poetry and, at night, looked to the sky and the stars, wondering about what they saw.

These simple activities were the birth of astronomy. It was a simple beginning; people noticed the stars in the sky. Then, they named the stars. They noticed patterns among the stars. They also saw objects moving across the backdrop of stars from night to night and called them "wanderers" (which became "planets").

The science of astronomy grew over the centuries as scientists figured out what the different objects in the sky are and learned more about them by studying them through telescopes and other instruments.

The Birth of the Constellations

Besides stargazing, the ancients put the stars they saw to good use. They played cosmic "connect the dots" with the stars to create patterns that looked like animals, gods, goddesses, and heroes.

Then, they created stories about these patterns of stars, which are called constellations—or constellation outlines. Those stories are the basis of many myths that have come down to us through the centuries from the Greeks, Romans, Polynesians, Asian cultures, African tribes, and many more.

The constellation patterns and their stories date back thousands of years to many cultures.

 For example, the constellations Ursa Major and Ursa Minor, the Big Bear and the Little Bear, have been used by different populations around the world to identify those stars since the Ice Ages.

Most of the names we use today come from ancient Greece or the Middle East, a legacy of the advanced learning those cultures had. They played a huge role in navigation for people who explored the Earth's surface and oceans, as well. 

Contellations vs. Asterisms

If you're familiar with the constellations, you probably know about the Big Dipper. It's really more of a "landmark" in the sky. Although most people can recognize the Big Dipper, those seven stars are not really a constellation. They form what is what is known as an "asterism". The Big Dipper is actually part of the constellation Ursa Major. Likewise, the nearby Little Dipper is a part of Ursa Minor.

On the other hand, our "landmark" for the south, the Southern Cross is an actual constellation called Crux. Its long bar seems to point toward the actual region of the sky where Earth's south pole points (also called the South Celestial Pole). 

There are 88 official constellations in the Northern and Southern Hemispheres of our sky. Depending on where you live, you will probably see more than half of them throughout the year.

Study the stars in each constellation, and then as you get more familiar with them, start to look for other objects hidden among the stars. 

To figure out which constellations you're looking at in the night sky, you can use star charts (such as those found online at Sky& or Or, you can use planetarium software such as Stellarium (, or an astronomy app on your portable device. There are many apps and programs that will help you make useful star charts for your observing enjoyment.


Edited and updated by Carolyn Collins Petersen.