Telescopes: Eyes on the Universe

A telescope is a scientific instrument that collects light and makes distant objects appear larger and clearer. Astronomers use telescopes to study everything from the Moon to galaxies billions of light-years away. The bigger a telescope's lens or mirror, the more light it can gather — and the fainter the objects it can reveal.

Here is the key idea: a telescope is really a giant light-bucket. Your eye has a tiny opening, so it can only catch a little light. A telescope has a huge lens or mirror that scoops up far more light and funnels it to a single point. That is why a telescope can show you stars far too dim to see on your own.

There are two main types of optical telescope. A refracting telescope uses glass lenses to bend and focus light. A reflecting telescope uses a curved mirror to gather and focus light instead. Most large research telescopes today are reflectors because mirrors can be made much larger than lenses without sagging under their own weight.