• Question: How do those big telescopes work?

    Asked by mhorner to Sara on 20 Jun 2011.
    • Photo: Sara Imari Walker

      Sara Imari Walker answered on 20 Jun 2011:

      Hello mhorner! Sorry for the slow reply on this one! Somehow it was lost in my question Inbox.

      Big telescopes are really cool. They let us peer deep into the universe and see amazing things like other stars and galaxies. Somewhat surprisingly though, they don’t operate all that differently from normal small telescopes. Most modern telescopes are reflectors. This is to be contrasted with refractors if you have the interest to look those up – Galileo discovered moons of Jupiter, phases of Venus, and Sunspots with a refractor. It was the state of the art in its day!

      Reflectors are the best today. They work by using a single curved mirror or a combination of curved mirrors that reflect light and focus it to form a single image. The larger your reflecting mirror, the more light you collect and the better you can see. For most stars and galaxies the light reaching Earth is pretty faint, having traveled literally millions of miles to reach us. Large telescopes are therefore necessary to capture the few particles of light, known as photons, that reach us from these distant objects. The bigger the better! So people usually try to build as large a telescope as possible.

      There is a trade-off however, it is hard to design really precise mirrors if they are very big. For this reason there is a limit to the size of Earth based telescopes. To see even farther into the universe then, we launch space telescopes like Hubble. Telescopes in space can be small and still work much better than huge telescopes on Earth. Why? Because the atmosphere interferes with the light we get from objects. Have you ever noticed how stars twinkle? Well that is not because they actually fluctuate in intensity but instead it is because the atoms of our atmosphere bounce around the few photons that reach us. This is big trouble for large telescopes, which must counteract this effect with precision mirrors to get precise measurements. Or we go to space!

      Btw, nice pick of favorite scientists (and profile pic 😉 )

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