Bunnies hop. Toads hop. I hop. Wait – that might be a trademark. Lots of things hop. It’s not only a fun way to get from point A to point B, it’s a fun way to get from star A to star B. It’s the second in our bag of tricks for finding what we’re looking for through the Time Machine.
How do you star hop? It’s easy: Start by looking at something you know. Then hop from star to star until you’re looking at something else. You do this all the time when you give people directions to your house. It goes like this:
Take Main Street east out of town until it ends at the light. Turn left. Go three miles and turn left at the stop sign. Our house is the third one on the right. It’s hard to tell because there’s one in front of ours. Our house is the red one – the one in front is the blue one.
You’re giving people directions, but you’re giving them from a starting point that you assume they know how to get to in the first place. There are a lot of Main Streets that go east/west, but if they’re in the same town as you it’s safe to assume they know which Main Street you are talking about. Giving directions to someone who lives in California to your house in New York will be much different (take I-80 for 1000 miles. Make some turns in Kansas. Take I-70 for 1000 miles. Turn left at Ohio, take I-90 for 500 miles, and then you can talk about Main Street).
We do this very same thing all the time when talking about things in the sky. Let’s say you see a bright, reddish star that you want to point out to someone. You can’t just say “hey, look at that bright, reddish star” and expect them to know which one! You usually point. If it’s hard to see, you might say
See that bright one over there? Start by looking at that one and then move your eyes east about the width of both of your fists held at arms length. That takes you to that sort of circle of six stars. See them? Good. Now draw an imaginary line from the right two straight out until you get to that bright white star. See it? Okay, now see how it makes a triangle with those other two bright stars nearby? The star at the top of that triangle is the one I’m talking about. See it now?
This is star hopping. Using pointers, guide stars, real or imagined shapes in the stars, and other objects (trees on the horizon, telephone poles, whatever is around) to get from one point to another, given a known starting point. Star hopping is especially good to use for things we can’t see with our naked eye. Things like deep-space objects and nebula. More about those in another post, but let’s say that they’re things that are far away and usually too dim or diffuse for our eyes to see. So if we want to see them in binoculars or Time Machines, we can use RA/dec or we can star hop to get there.
Like a good Astropotamus, star hopping is really moving around in time. Stars are not fixed to the surface of some globe in space. They are close (a few dozen or hundred light years away) and far (a few thousand or tens of thousands of light years away). Their apparent closeness to each other is the same way that a picture of a city skyline makes the buildings look like they’re all in a row, when in reality, they’re often miles apart.
One famous star hop that you can do with your friends and family is to find Polaris, the North Star. It’s in the constellation known as Canis Minor, commonly referred to as the Little Dipper*. It’s conveniently placed really really really close to the celestial pole (hence the name), but it’s pretty dim. So it can be hard to pick out sometimes. But the nearby Big Dipper** is pretty easy to spot and provides a really nice set of pointer stars to find Polaris. I won’t tell you how, since a good picture tells a thousand words.
Note that I stole this from another web site, so please check them out for more information on star hopping. Also note that the Dippers are called Ploughs in the UK***.
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*An asterism is a collection of stars that make a picture but aren’t really a constellation. The Little Dipper is an asterism, as the stars that make it up are actually part of Canis Minor.
**The Big Dipper is an asterism, too. Its stars make up part of Canis Major.
***Asterisms, especially, are called different things in different places. That’s why constellations have agreed to names and configuration by the International Astronomy Union – they are the same everywhere.