The first visible light telescope, invented 400 years ago, used an arrangement of lenses and was small enough to hold by hand. Modern telescopes are much larger,
so that more light can be caught and fainter objects can be seen. Curved mirrors are used to focus the light and record it on sophisticated electronic equipment.
The 5 meter (200 inch) Hale telescope on California's Palomar Mountain, completed in 1948, was the largest telescope for several decades. This honor is now held
by the two Keck telescopes on Mauna Kea in Hawaii, each with a mirror diameter of 10 meters.
To minimize image blurring due to the Earth's atmosphere, telescopes are usually built on high mountains. Mirror deformation technologies now also exist
to correct for atmospheric blurring. But even better results are achieved with a telescope in orbit above the Earth atmosphere, such as the Hubble Space
Telescope. It has a 2.4 meter diameter mirror in a satellite the size of a school bus. It has produced some of the sharpest and most stunning images ever
obtained, has found supermassive black holes in many galaxies, and continues to revolutionize our understanding of the Universe.
The 10 meter Keck telescopes on Hawaii's Mauna Kea mountain. Grasp the scale by looking at the cars in front of the building.