ICY SCIENCE: SCIENCE SPACE ASTRONOMY Spring 2014 | Page 11

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a certain size, you start to see just pixels, so there is no gain. Yes you can magnify it a billion times, but the
results will look horrible, and the same is true of telescopes.

So - there must be another limit we’re hitting up against, and anyway why do people want bigger telescopes? They’re always going on about the size of their mirrors, but as we’ve seen it doesn’t really help
magnify things that much. So why the ‘aperture fever’?

The problem is that even with the best optics in the world, and perfect “seeing”, light does not focus down
to a single point, even from a point source like a star. What you actually get is a series of concentric circles.
The middle is the bright and slightly fuzzy circular point, but then there are rings expanding outwards and

So this is the limiting factor. If we’re trying to
look at fine detail, we’ll eventually find the two
disks overlap, and what is two things blurs into
one. It’s caused by collision of light waves inter-

Airy’s formula

fering with each other as they enter the telescope and are brought to a focus.

So - can we do anything about it? Well, yes
we can - you probably knew that was coming,
and you probably can guess at the answer. The
formula for how big this circle is, is given by
Airy’s formula
ICY SCIENCE | QTR 2 SPRING 2014