Constellation Guide

What Is a Constellation?

A constellation is a pattern of stars that ancient skywatchers grouped together and named, usually after a figure from myth, an animal, or an object — not because the stars are physically related to one another, but simply because they appear close together from Earth's point of view, often at wildly different real distances from us and from each other. Many of the patterns still in use today, including most of the ones in this guide, were catalogued nearly two thousand years ago by the astronomer Ptolemy, who listed 48 constellations in the 2nd century AD.

What changed since Ptolemy's time is precision. In 1922, the International Astronomical Union formally adopted 88 constellations covering the entire sky, and in 1930 the Belgian astronomer Eugène Delporte drew official boundary lines between them, so that every point in the sky — not just the bright, recognizable patterns — now falls within exactly one constellation's borders. That's the modern, scientific sense of the word: less a picture, more a labeled region of sky, the same way a country's borders exist whether or not you're standing at any particular landmark inside them.

Twelve of the 88 sit along the ecliptic, the path the Sun appears to trace across the sky over a year, and make up the zodiac; the rest, including a few of the most famous constellations of all, sit elsewhere across the northern and southern sky. This guide covers 16 in total — all 12 zodiac constellations, plus four other especially well-known ones — with the mythology behind each, the real astronomy inside its borders, and the option to have a star of your own named and plotted within it.