The Sky Above

You may be surprised to learn that astronomers, on average, know very few of the constellations in the night sky. The imaginary stick figures serve very little purpose in modern astronomy. Their value today lies primarily in their ability to help amateur astronomers point their telescopes in the right part of the sky. Ok, now I know what you’re thinking. “What do you mean astronomers don’t know the constellations!?! That’s what I thought this whole course was about. I hate you!” Ok, maybe you’re not thinking that exactly, but you’re probably surprised that constellations just aren’t that important in astronomy. Watch the teacher video Perspectives on Constellations for an explanation of why.
Play with Big Dipper 3D simulation to see how the actual stars that make up the big dipper are not as close to one another in 3D space as you might expect.
So what about all those awesome stories - the mythology connected to the constellations? Do astronomers study that? No, I’m sorry. We don’t. Check out the video What Disney’s constellations can teach us about astronomy to see why.
All that said, I still want to provide you with the opportunity to learn how to find constellations in the night sky (even though it will not be a central part of our course). Watch the teacher video Finding Constellations, which shows you how to build and use a star chart to find constellations in the night sky. You can print your own star wheel using the directions How to Make a Star Wheel the Simple Way. A little later in this unit, I will also show you some free tools that can help you locate objects in the sky.
To understand the night sky, it is helpful to imagine that the sun, moon, stars, and planets are all located on an imaginary giant glass sphere surrounding the earth. We call this imaginary dome, “the celestial sphere.” Read 2.1 The Sky Above for an introduction to the concept of the Celestial Sphere.
As we try to describe the motion of the sun, stars, and planets in the sky, we need a way of describing the location of objects in the sky. We will learn that there are several ways to do this, but the first and simplest we will encounter is the Horizon Coordinate System.
One of the best ways to explore and understand motions in the night sky is with “planetarium software.” My favorite is Stellarium-Web, which runs right in your internet browser. Watch this Overview of Stellarium Web to learn the basics of navigating the program. (A more powerful (and still free) version of Stellarium can be installed on your computer. You can find the download at Stellarium.org and a free mobile version, “Stellarium Mobile,” is available for Android and Apple devices.)
We now have all the tools we need to understand the daily motion of stars in our sky. Watch the video Star Motion to see how it fits together. If you’d like to play with the simulations used at the end of the video, you can find it on this Paths of the Stars page.
The sun rises and sets each day, but it also moves through the entire celestial sphere once each year. It can be hard to picture this motion in our minds, so check out the video Apparent Motion of the Sun to see it visualized.