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From its 17th-century origins to its current deployment for scanning vast distances across space, the telescope has served as our eye on the sky, revealing the universe as a complex, beautiful place in which Earth is just one of countless marvels.
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Jupiter, the largest
planet in the solar system |
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The refractive telescope designed by Galileo
Though Dutch spectacle maker Hans Lippershey is often credited with inventing the first telescope in 1608, it is an Italian, Galileo Galilei, who gained fame — and infamy — for using it for astronomical observation.
The world has not been the same since Galileo unveiled his telescope in 1609. His design employed a lens to refract parallel light rays, causing them to converge at a focal point.
When Galileo trained his refractive telescope on the heavens, he turned the world on its head. He observed the surface of the moon, the rings of Saturn, Jupiter's four largest moons, and the phases of Venus.
Sir Isaac Newton, born in 1642, determined that refractive telescopes dispersed light into colors. To eliminate this color aberration, he ground metal mirrors for a reflecting telescope, superior to a refractor due to the wider diameter of its mirror. Newton's design used a curved primary mirror and a flat diagonal secondary mirror.
These mirrors act as "light catchers"; the bigger the mirror, the more light collected. Today, reflectors are used in observatories all over the world.
Astronomical Telescopes
↑Refractive telescope (Galilean type)
The objective lens converges light, and images are magnified at
the eyepiece.
↑Reflecting telescope (Newtonian type)
In a reflector telescope, light reflected from a mirror, not
through a glass lens, creates the images. This design eliminates "the
rainbow effect," or color aberrations, characteristic of
refractive lenses.
The 60-inch (1.5-meter) telescope at Mt. Wilson Observatory
The universe is massive — so massive that at times it seems beyond our comprehension. For example, our closest neighboring galaxy, Andromeda, is 24 quintillion kilometers away. That's "24" followed by 18 zeros. Such numbers are too large and unwieldy to be practical.
Astronomers measure space in light-years, the distance light travels in one year. Light moves at approximately 300,000 km (186,000 miles) per second, so a light-year is roughly 9.5 trillion km (5.9 trillion miles). The consensus is that the radius of the universe is about 13.7 billion light-years.
"What's it like to look at the end of the universe from Earth?" asks Dr. Fumihide Iwamuro, an associate professor at Kyoto University's Graduate School of Science. "It's as if you were far smaller than a single atom and were looking up at the Earth."
Since Galileo and Newton, scientists have developed telescopes built to specifications larger than anything the Renaissance astronomers could have envisioned.
Dr. Iwamuro says the observatory at Mt. Wilson, California, is a prime example. Using a mirror purchased for him by his father in 1894 and configured by George Willis Ritchey, George E. Hale set the 60-inch (1.5-meter) mirror on the reflector mount in 1908 and started research, photography and other astronomical operations.
"The silver-coated glass in the primary mirror was precisely ground," Iwamuro explains. "It enabled Hale and Ritchey to obtain stable, quality images from deep space. Its secondary and tertiary mirrors were designed to switch light to focus images at three different focal points, each assigned a specific task, enabling work on multiple projects immediately."
Iwamuro says charge coupled devices (CCDs) have helped astronomical observation immensely. A CCD is made up of millions of pixels that convert light (photons) into electrons. When struck by light coming through a telescope, the pixels convert the light into electrons, which are then changed into an image.
"CCDs arrived on the scene around 1980," Iwamuro explains. "Before that, light from celestial bodies was fixed onto photographic plates, which had limitations. With CCDs, photographic sensitivity increased up to 40 times."
The Subaru Telescope
(Courtesy of NAOJ)
The Mt. Wilson Observatory ushered in the 20th century, the golden age of astronomy. Telescopes grew and discoveries proliferated.
The famous W.M. Keck Observatory is perched atop 4,205-meter (13,796-foot) Mauna Kea in Hawaii. It is home to the world's largest optical telescope, an eight-story, 300-ton mammoth with a 10-meter (393-inch) primary mirror made up of 36 hexagonal segments that work as a single reflector. The $140-million facility is surrounded by nothing but ocean, in a dry climate ideal for astronomical observation.
Sharing Mauna Kea is the Subaru Telescope, operated by the National Astronomical Observatory of Japan (NAOJ), National Institutes of Natural Science. The 8.2-meter (323-inch) telescope — the largest monolithic-mirror-type scope at the time of its inauguration — began operations in January 1999. In September 2006, astronomers used it to discover the most-distant galaxy known to man, 12.88 billion light-years from Earth.
There are plenty of humongous astronomical telescopes around the world. But the most famous telescope isn't on the Earth. It's the Hubble Space Telescope, orbiting our planet since 1990.
Earth-bound telescopes, even on mountaintops, are affected by earthly phenomena: storms, light, pollution, the atmosphere. But in space, the Hubble's modest 2.4-meter (94-inch) mirror can detect light from celestial objects without interference. It has probably done more for astronomy than any other telescope in history. But scientists aren't stopping there: Hubble's successor, the James Webb Space Telescope, could be operational in less than a decade.
