Telescopes from the Ground Up
One of Galilleo's illustrations of the moon.

Galileo’s Refractor

A new instrument launches the science of astronomy

In 1609, an Italian mathematics professor named Galileo Galilei peered through a strange new device at the stars. Suddenly, the night sky, so well known and familiar, revealed itself as a barely explored mystery.

The Moon is a gray-white orb to the naked eye. Looking through the new instrument, Galileo saw shadows and bright spots that showed the surface had mountains and valleys. The planets, thought to be odd stars that “wandered” the sky, now looked like little globes. Galileo discovered that the planets were accompanied by moving pinpoints of light — their own moons.

Galileo quickly published his discoveries in a bulletin he titled “Message from the Stars.” His claims were met at first with wonder and excitement. He presented his device — eventually named a “telescopio,” Greek for “to see at a distance” — to the leaders of the time, including the Catholic Church in Rome.

A simple design

Galileo’s telescope was a simple instrument compared with the ones we use today. It was a tube with two lenses — the convex primary lens that curved outward, and the concave eyepiece lens that curved inward. He built the device after hearing about the newly invented spyglass, an instrument used by the military to peer into enemy camps.

Image above: Courtesy Royal Astronomical Society
Click here to see all avaliable eras.