Monday, September 7, 2009

The Most Important Telescopes In History

The Most Important Telescopes In History


The most important telescopes in history

In celebration of the International Year of Astronomy in 2009,
here is a tour of some of the most important telescopes ever built.


Galileo's refractor (1609)

The exact origin of the telescope is still controversial. The oldest existing documents attribute its invention to the Dutch spectacle maker Hans Lipperhey in the early 17th century. Lipperhey found that placing a convex lens at one end of a tube and a concave lens at the other allowed him to magnify distant objects.

Though he didn't invent the telescope, Galileo improved on its design - gradually increasing its magnification power. And he was the first to realise that it could be used to study the heavens rather than just to magnify objects on Earth.


Newton's reflecting telescope (1668)

Instead of using glass lenses to bend, or refract, light, Isaac Newton used a curved mirror to reflect light to a focal point. This design, which uses mirrors as buckets to collect light, can magnify objects far more than is possible with a lens. It also minimises the problem of chromatic aberration - colour defects that are caused by the lens bending different wavelengths of light by different amounts.

However, due to problems with accurately grinding the metal mirror, Newton's first reflector, a replica of which is seen here, actually caused more image distortions than other contemporary telescopes. As a result, more than a century passed before reflecting telescopes became popular among astronomers.


Herschel's telescopes

In the late 1700s, German musician William Herschel and his sister Caroline began making large reflecting telescopes. With a mirror measuring 1.2 metres in diameter, Hershel's largest telescope (pictured) was an unwieldy instrument, requiring four servants to operate its wheels, ropes and pulleys. It remained the biggest telescope in the world until the mid-eighteenth century.

Herschel scanned the heavens systematically and catalogued hundreds of nebulae and binary stars (in 1781, with a smaller telescope, he discovered that an object previously thought to be a star was in fact the planet Uranus). In the 1830s, Herschel's son John spent a few years in South Africa, where he set up a similar, but smaller telescope to study the southern skies.


Yerkes refractor (1895).

American astronomer George Ellery Hale was behind the construction of a refracting telescope with a 1-metre-wide primary lens - at the time, the world's largest telescope - at the Yerkes Observatory in Williams Bay, Wisconsin. Ground by American telescope builders Alvan Clark and Sons, the primary lens was completed in 1895 and is still the largest ever made. But refractor builders had reached their limit with the Yerkes Telescope - larger lenses would sag under their own weight, among other problems, so telescope makers turned once again to reflectors

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