Observatory

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Space Observatories

Observatories high above Earth’s turbulent atmosphere make it possible for astronomers to see the universe much more clearly than with ground-based instruments, as well as study wavelengths of radiation that are blocked by the air.

Some of the many space observatories now in Earth-orbit are part of NASA’s Great Observatories Program. The first of the series was the Hubble Space Telescope (HST), launched in 1990, followed one year later by the Compton Gamma-Ray Observatory (CGRO). The Chandra X-Ray Observatory was placed in orbit in 1999, and the Spitzer Space Telescope was launched in 2003.

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History

The telescope is a relatively new invention, but astronomical observatories are not. Even in ancient times, sky watchers built and used observatories. Records that are 5,000 years old show that the Babylonian civilization, in what is now Iraq, observed the movement of celestial objects. About 4,500 years ago, Egyptians developed a calendar based on the movement of the Sun, showing that ancient Egyptians watched the movement of heavenly bodies. Most scientists believe that the stone pyramids of the Maya civilization, mostly in southern Mexico and dating from 2,500 years ago, have astronomical significance. One of the most mysterious ancient observatories is Stonehenge, an arrangement of stones surrounded by a circular earthwork in southern England. Stonehenge, which dates from the late Stone and early Bronze ages, may have been used by prehistoric peoples to predict eclipses and to tell time.

Most historians believe that Dutch spectacle maker Hans Lipperhey built the first known telescope in 1608. The Dutch used telescopes as military tools to spot ships approaching from a distance. In 1609 Italian astronomer Galileo Galilei built a telescope to study the sky.

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Although his telescope could magnify only 20 times, Galileo discovered many things, including the cratered surface of the moon, the constantly moving moons of Jupiter, the changing phases of Venus, and the countless stars that make up the wispy light of the Milky Way. Galileo’s observations helped overturn the idea that Earth was the center of the universe, and opened the door to the true science of astronomy.

The first telescopes used glass lenses to gather and bend light to a focus. These refracting telescopes could be fairly powerful, but were very long, and were hard to steady and balance. Near the end of the 18th century, English scientist Sir Isaac Newton built a telescope that used a mirror instead of a lens. The first of these mirrors were made of speculum metal (a mixture of copper and tin), but glass mirrors soon replaced the metal.

Because of the better balance of refractors and because large mirrors are lighter than large lenses, telescope makers could make larger reflecting telescopes than refracting telescopes. The large reflectors could see much farther into the universe and reveal many more mysteries. Soon some telescopes were so large they could be moved only by complex pulley systems. Eventually they grew so large that astronomers needed buildings to protect them from the weather. Many of these buildings were constructed in the shape of domes with moveable slits that could be opened to the outside.

Through the centuries, telescopes continued to grow. Eventually the mirrors became so large and heavy that it was almost impossible to build telescopes sturdy enough to hold them, and yet light enough to point the mirrors at different areas of the sky. Instead of using single large mirrors, in the 1970s and 1980s telescope makers began building telescopes with multiple, or “segmented,” mirrors. Advances in computer technology meant that observatories no longer needed complicated telescope mountings—the telescope could stand on a simpler mount and the computer could determine the exact movement needed to follow an object across the sky. At this time, observatories began to take on unconventional shapes. Some observatories built in the later part of the 20th century were large square buildings, instead of the usual cramped round buildings. The new buildings improved the flow of air around the telescopes, preventing distortion from regions of different temperature.

In the 1990s, the largest observatories in the world opened to the sky. The mirrors of the two Keck telescopes on Hawaii’s Mauna Kea are each about 10 m (33 ft) across. The Very Large Telescope (VLT) of the European Southern Observatory uses four telescopes—each 8.2 m (27 ft) across—joined together to create the light-gathering power of a single instrument 16 m (52 ft) in diameter.

In less than five decades, telescope light-gathering power has more than tripled. As the 21st century opens, half a dozen more telescopes—each more than 6.5 m (21 ft) across—are being constructed in joint projects by countries such as the United States, Great Britain, Canada, Brazil, Argentina, Italy, Chile, and Japan.

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