The First Telescopes

The very first telescopes were believed to have began to appear around the year 1608 and were credited to opticians Hans Lippershey and Zacharias Janssen as a type of spyglass. These early refracting telescopes consisted of a convex objective lens and a concave eyepiece and the telescope simply slid inside itself to focus.Galileo greatly improved upon this design and is often credited as being the first to invent the first astronomical telescope.. In 1611, Johannes Kepler described how a telescope could be made with a convex objective and eyepiece lens and by the year 1655 astronomers such as Christiaan Huygens were building powerful but extremely large and bulky Keplerian-design telescopes with compound eyepieces.

By the year 1616, Niccolò Zucchi had designed the first reflecting telescope, but the design was impractical. By 1688, Sir Isaac Newton had solved the problems of Zucchi’s reflector by adding a small flat diagonal mirror to reflect the light to an eyepiece mounted on the side of the telescope. During 1688, Laurent Cassegrain initiated the design of a reflector with a small convex secondary mirror to reflect light through a central hole in the main mirror. In 1733, Chester Moore Hall went into telescope history with the first achromatic lens refractor and John Dolland independently came up with the same design five years later producing telescopes and marketing them. John Hadley was working to improve reflecting telescopes in 1721 by creating larger paraboloidal mirrors, but it would be 1857 before Léon Foucault came up with a good process for coating them, known as silvering. Believe it or not, it would be 1932, before long lasting aluminized coatings on reflector mirrors would become a standard!

Telescope History – 20th and 21st Century

The first radio telescope was built by Grote Reber in 1937, and many types of telescopes were developed in the 20th century for a wide range of wavelengths from radio, to gamma-rays. Interest in radio astronomy grew after the Second World War when much larger dishes were built including: the 250 ft. Jodrell bank telescope in 1957, the 300 ft. Green Bank Telescope in 1962, and the 328 ft. Effelsberg telescope in 1971. The huge 1000 ft Arecibo telescope came along in 1963, and it is so large that it is fixed into a natural depression in the ground. The central antenna can be steered to allow the telescope to study objects up to twenty degrees from the zenith.

The first Gamma Ray telescope was the Compton Gamma Ray Observatory built in 1991. Very high-energy gamma-rays (above 200 GeV) can be detected from the ground via the Cerenkov radiation produced by the passage of the gamma-rays in the Earth’s atmosphere. Several Cerenkov imaging telescopes have been built around the world including: the HEGRA in 1987, STACEE in 2001, HESS in 2003, and MAGIC in 2004.

X-ray telescopes, known as Wolter telescopes, have been in use in satellites since the 1940′s. Some of the OAO satellites conducted X-ray astronomy in the late 1960s, but the first dedicated X-ray satellite was the Uhuru in 1970 which discovered 300 sources. More recent X-ray satellites include: the EXOSAT in 1983, ROSAT in 1990, Chandra in 1999, and Newton in 1999.

Ultra-violet telescopes began as early as 1962. The International Ultraviolet Explorer in 1978 systematically surveyed the sky for eighteen years, using a 45 cm (18 in) aperture telescope with two spectroscopes. Extreme-ultraviolet astronomy (10-100 nm) is a discipline in its own right and involves many of the techniques of X-ray astronomy. The Extreme Ultraviolet Explorer in 1992, was a satellite which operated at these wavelengths.

The launch of the IRAS satellite in 1983 revolutionized infrared astronomy from space. This reflecting telescope which had a 60 cm (23 in) mirror, operated for nine months until its supply of coolant (liquid helium) ran out. It surveyed the entire sky detecting 245,000 infrared sources and more than 100 times the number previously known.

The Most Famous Telescope In History

In 1962, the USA’s National Academy of Sciences recommends building a large space telescope. In 1977, Congress votes to fund the project and construction of Hubble Space Telescope begins. Construction of Hubble Space Telescope was completed in 1985. The launch of Hubble was delayed due to the 1986 Space Shuttle Challenger disaster. Hubble was launched on the space shuttle on April 25, 1990.