ICY SCIENCE: SCIENCE SPACE ASTRONOMY Spring 2014 | Page 14

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OK - so now we have an equation with a bunch of numbers in that tell us how big the blurry spot will be.
There are a bunch of things on the top line, but they are all constant. So there is nothing we can do about
those (well we could go to shorter wavelengths, but we said we’ll stick with visible green light).
So the only thing we can play with is the value of d. If we make d smaller, the angle gets bigger. In case you
can’t see this, lets replace the numbers on the top with 10. Now if we have d of 5, then the angle is 2, a d of
2 makes an angle of 5, a d of 1 makes it 10. So you can see as d gets smaller the angle, and hence how blurry
the image is, gets bigger. If we make the mirror bigger though, the angle gets smaller, and each star forms
a smaller spot. So we can see more detail, split stars and so on. This is crucially why big mirrors are better
than small mirrors. When you magnify up the image, you can go further before it all becomes a mess. It’s
like having more megapixels on your camera! So that is why astronomers want ever bigger mirrors.

However, if we go back to the equation, and
look at changing the wavelength, we can see
something else. If we switch to radio waves,
which are huge compared to light waves, we
can see what happens. It explains why telescopes like the Jodrell Bank radio telescope are
so big. If we write out the formula putting in
the radio waves that a radio telescope generally
looks at, for instance 10cm, what does that do?

ICY SCIENCE | QTR 2 SPRING 2014