7. How a reflecting telescope works - use in astronomy

A reflecting telescope uses a concave mirror

A relatively large concave mirror collects as much light as possible from distant astronomical object e.g. a star, so a reflecting telescope has found extensive use in astronomy.

The collected light is reflected by a small plane mirror at ~45^o into an eyepiece or camera.

By means of a magnifying lens in the eyepiece tube you can produce a clear focussed and greatly magnified image of the star or any other distant object.

This type of reflecting telescope is also known as the Newtonian telescope (or Newtonian reflector) because it was invented by the English scientist Sir Isaac Newton. He used a concave primary mirror and a flat diagonal secondary mirror and his first designed reflector was completed in 1668.

Technically, the Newtonian reflecting telescope is made of a primary mirror or objective mirror, usually parabolic in shape, and a smaller flat (plane) secondary mirror. The primary mirror collects light from the pointed region of the sky and the secondary mirror redirects the light out of the optical axis at a right angle so it can be viewed with a magnifying eyepiece.

Using SEARCH some initial results may be ad links you can ignore - look for docbrown

INDEX notes: Light reflection and uses of plane & curved mirrors