Telescopes from the Ground Up

Catching some rays

Once astronomers learned to make parabolic mirrors, they could create reflecting telescopes that had neither spherical nor chromatic aberrations. Not only were these the first telescopes to produce clear images of the sky, they had shorter focal lengths, so were more compact and easier to use.

Get to the root of it

It wasn’t long before astronomers began building big telescopes again — this time, because they were constructing larger and larger primary mirrors.

The bigger the mirror, the more light it could collect. Large mirrors enabled telescopes to see increasingly distant and dim objects.

From this point on, the size of the primary mirror — not the length of the telescope — would indicate how powerful the telescope was. Reflecting telescopes still got bigger, but only because the mirrors that had to fit inside were being made larger.

Mirror image

Large reflecting telescopes became quite popular. The glass lenses of the refracting telescopes were improving, but it was easier to make a metal mirror than a glass lens. Mirrors just had to be shiny and the correct parabolic shape in order to work in a telescope. Glass lenses, on the other hand, had to be absolutely perfect — free of imperfections in the glass or slight errors in shape — or light would be distorted as it passed through.

Click here to see all avaliable eras.