As the weather gets nicer, it’s not only great for going out in the day, but also for going outside at night. There’s a lot of great science happening both during light and dark hours. In fact, observing dark skies is a scientific study all by itself!
Sometimes we take it for granted, but the reason why the sky is dark at night is not only because our side of Earth rotates away from the Sun, but because there’s a lack of other light as well. This tells us something about everything else in our Universe and how far away all sources of light must be and what they must be doing. (This is related to something called “Olber’s Paradox,” and it’s fun to read and think about, especially before you go outside to look at stars.) It’s also important that our own light from our neighborhoods and cities are not flooding our skies with their own light. If the canvas of the sky isn’t dark, then we aren’t able to see it contrast with dim stars.
You can measure how much extra light is in our sky by counting how many stars you can see — the more stars you see, the darker the sky must be. This is easier to do than you might think, and we’ve left some instructions below the break on this page that you can use to do this. You can compare your star counts on different dates and in different locations to see what happens to your star counts. We’ll record your star counts on this form as part of a project to analyze our dark skies locally. (Or, if you want to follow the instructions and only record the data for yourself, that’s a great project, too.)
If you’d like to share your data with an even bigger project, you can take a look here at the Globe At Night program . They have their own program and form to report your view of the sky by looking at specific constellations that they help you find. Then, this data gets compiled with other observations from all over the world. You can see some of their results here.
This is an exciting project for a few reasons. First, it’s a way to see how our own lighting affects what we see at night, which can have big implications that you might not even realize. The International Dark Sky Association shows examples from right here in Utah that you may have visited:
How familiar you are with the night sky, navigation, and even culture is dependent on being able to see stars against a dark background. But most of all, we think that it’s awe-inspiring to see a dark sky, maybe even with a view of our own Milky Way Galaxy stretched across the sky.
The first step to seeing any of this is simply to go outside in a comfortable place, let your eyes adjust, and look up on a clear night. Even if you do nothing else, just look up an imagine. You’ll start to see more than you might expect.
The other thing we love about star counting projects is that these are part of a larger collection of work called “Citizen Science” projects. These are scientific pursuits that you can help with by reporting your own data. Besides the Globe At Night program and the International Dark Sky Association’s own promotion of the program, there are completely different projects you can help with. We might highlight some of these in the future, but here are a few examples:
- Our own National History Museum of Utah features a collection of citizen science projects that could be especially relevant to you here in Utah.
- The projects showcased at Zooniverse extend more globally and even throughout the universe! (You can help categorize galaxies, observe ocean life, record migration patterns, etc.)
Whatever you do — even if it’s just for yourself — recognize that the observing and appreciating is a big part of how science gets started. Let us know what you start to see, and let us know if you have questions along the way!
Instructions for counting the stars in your sky
On a clear, dark night, go outside at a location of your choice — your backyard is great — and count the stars! Instead of counting all of them, however, you will count them as you look through a toilet paper tube. (Maybe this is why people are buying so much toilet paper these days?)
After your eyes are adjusted to the dark, hold the tube to your eye and point it in a random direction and count how many stars you can see in that part of the sky. This is a sample of the sky. Do this 8 times, each time pointing in a different, random part of the sky. Write down your counts so that you can analyze them when you go back inside.
Once back inside, you can also get your location’s approximate star count by:
- Adding up your 8 counts all together, and then
- multiplying that sum by 9 (assuming you use a toilet paper tube, because this factor describes how much of the sky you were sampling with this device).
For comparison, if you had a completely dark sky and well-adjusted eyes, you could be able to see almost 5000 stars with the unaided eye. How did your measurement compare? How do you think it would be different in different locations? (You should try other places , too, when you have the chance!)
You can also do more research on dark skies and light pollution. A good place to start is here:
where the International Dark Sky Association provides other information and tools for doing more star counts. They also describe why this is an important issue — but you might think about this yourself before you read more.