When it comes to learning the night sky, constellations can be very confusing and asterisms can be very helpful. But to understand why, let’s make sure we know which is which.
- Asterism - An informal collection of stars that form a simple pattern.
- Constellation – A collection of stars that frequently represents a traditional figure from mythology. The entire sky is divided into 88 such constellations with specific boundaries that are recognized by international agreement.
Many people have never heard the word asterism, but they probably know one or more asterisms, and chances are they think these asterisms are constellations. Best example: The Big Dipper. It’s not a constellation. It’s an asterism. That is, it is an informal collection of seven stars that form the pattern of a water dipper. But this asterism is a significant part of a much larger constellation known as Ursa Major, the Great Bear.
Now here’s the problem. Asterisms are invariably simple. They are usually made of just the brightest stars, and they form patterns that are easy to recognize and remember. Constellations can be quite complex; to make them look like their names imply, you frequently have to use stars that are too faint for suburban observers to see, and even then they seldom really look like the mythical figures they represent. Even their names can throw the modern ear for a loop. Do you know, for example, what a camelopardalis is? The myths associated with them, while interesting and fun, are rarely known by modern people. But don’t take my word for it. Here. Give it a try. Take the Constellation Challenge. Use the link below to download a version of the following image suitable for printing, and see how you do. (Of course you can do this in your mind on the computer screen if you like.)
Now try the Asterism Challenge.