ICY SCIENCE: SCIENCE SPACE ASTRONOMY Spring 2014 | Page 13

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Woah, what’s all that gibberish?? Well lets break it down a little and see, it’s
not so hard.

sinθ- well this is the sin of the angle θ(which is the greek letter theta)

of the first ring. The angle is how big that fuzzy disk is going to be. Why θ- I’m
not sure, but angles in maths and physics nearly always use the greek letter
θfor some no doubt historic reason. Do you remember sines, cosines and tangents? No - oh well never mind. One neat trick is that the sin of a very small
angle is almost the same as the angle itself. It all goes wrong as the angle gets
bigger, but it means that for small angles sinθ≈θand the angles we’re looking
at are typically very small.

≈this just means approximately equal to - so maybe not to several

decimal places, but generally good enough.

1.22 is just a number, I’m sure you’ve met those before

λis the greek letter lambda, and is used in physics for wavelengths (in

this case of light).

and d is the diameter of the objective lens/mirror.

We can simplify this somewhat. Lets stick with green light, which is about in
the middle of the visible band. This has a wavelength of around 550 nanometers, or 550x10-9 meters. So we can now simplify the