Unit 9 : Constellations : Circumpolar : Spring : Summer : Autumn : Winter : Unit Questionnaire

Unit 1: How to Point to a Star
Unit 2: Where on Earth Are You?
Unit 3: Earth's Rotation and the Sun's Apparent Motion
Unit 4: Yearly Changes in the Sky
Unit 5: Seasons and Climate
Unit 6: Sundials
Unit 7: Navigation
Unit 8: Ancient Astronomy
Unit 9: Constellations

What are constellations?

What is a constellation? Most people picture a constellation as a pattern of bright stars connected with lines to get an often very sketchy picture. This definition is not entirely complete. Let's start with an analogy. Here we have a picture of central United States at night.

You can see several major cities and a lot of smaller ones. You could connect some of the brighter ones within each state and say "Here is the Minnesota constellation" or "Here is the constellation Illinois" but that would leave a lot of territory in limbo. So, instead, we define boundaries that separate Minnesota, Iowa, and Illinois and these make sure that every patch of land lies in one state or another.

Similarly, the sky is divided into odd-shaped patches. Inside each patch there is a pattern of stars that we use to remember the constellation, but the whole patch is counted officially, and every star belongs to one of these patches. Here are two pictures of Orion, one showing just the pattern and the other showing the boundaries:

The constellation Orion with the stars connected. Screen Capture from Starry Night.


The constellation Orion with the entire constellation boundary enclosed in the blue lines. Screen Capture from Starry Night.