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Publié le : 11/5/2013 -Format: Document en format HTML protégé

Observatory - astronomy.
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Observatory - astronomy.
I

INTRODUCTION

Observatory, building from which astronomers observe celestial objects such as planets, stars, and galaxies. The main instrument in an astronomical observatory is
usually a telescope, a device that gathers light from distant objects and makes them appear larger than they do with the naked eye. See also Astronomy.
Scientists keep sophisticated instruments such as telescopes, cameras, computers, and other electronic devices inside observatories to protect them from moisture,
sudden temperature changes, and other dangers caused by outside weather. Astronomers use this equipment to analyze light beams coming from space and celestial
bodies. This light helps them study the physical and chemical properties of the objects.
People also use the word observatory to refer to the complex of buildings where astronomers go to carry out research. One such complex, Kitt Peak National
Observatory west of Tucson, Arizona, is a complete mountaintop city. At Kitt Peak, astronomers from around the world have access to dozens of telescopes, electronic
and machine shops, and laboratories. Kitt Peak also includes a library, dormitories, a cafeteria, and even has its own water supply, electrical generators, and firefighting equipment.
Astronomers build observatories in places where Earth's atmosphere creates the least amount of interference between the telescope and space. Interference occurs
when particles in the atmosphere, such as water molecules, reflect and distort light. Astronomers look for sites where the weather is clear and the air is calm and dry.
Most modern observatories are on high mountaintops far from cities. At high altitudes, Earth's atmosphere is thinner, allowing astronomers to see the universe more
clearly. It is also important that the nighttime sky at an observatory site be free from city lights or interference from human-made radio sources. Artificial light and radio
sources can pollute telescope observations with unwanted signals.
Astronomical instruments are also carried into orbit around Earth, where the atmosphere does not interfere with their observations. Observatories such as the Hubble
Space Telescope orbit far above Earth and can see the cosmos more clearly than any ground-based instrument in operation. These observatories are usually operated
remotely by scientists on the ground. See also Space Telescope.
Other fields of science, such as the study of volcanoes (volcanology), the study of earthquakes (seismology), and the study of Earth's weather (meteorology), also use
buildings called observatories to house their equipment and to carry out research. However, the term observatory usually means a place of astronomical observations.

II

EQUIPMENT

Astronomy covers a broad range of research, and astronomers use many different types of equipment. The most familiar kind of observatory holds an optical telescope
designed to look at visible light, but many other types of observatories and telescopes exist. Astronomers who wish to study other types of light need special telescopes
and equipment, and the design of observatories reflects the equipment they contain.

A

Optical Telescopes and Domes

In a normal optical observatory, the most prominent instrument is the telescope. A typical modern telescope is a huge tube with a giant concave (dish-shaped) mirror or
collection of mirrors at one end. This mirror collects light from space and focuses it to a point. The telescope takes this gathered light and usually sends it into a camera
or other electronic instruments for analysis.
The dome, or housing, protects the telescope and other equipment from the elements. Domes open to allow the telescope access to the sky. Most domes have a single
slit down one side. When astronomers begin their work at dusk, they open the dome slit and allow the telescope to peer outward into the universe.
During the night Earth rotates, so as observed from Earth, the stars seem to move in the opposite direction. The telescope must take this into account and turn in the
opposite direction of Earth's rotation to remain focused on a stationary celestial object. The dome of an observatory also turns so the slit in the dome always allows the
telescope to see out. Many telescopes stand on special mounts that have one axis parallel to Earth's axis (the line around which Earth rotates) and the other at right
angles to the Earth's axis (or parallel to the direction in which the stars seem to be moving). This type of mount is called an equatorial mount. The axis parallel to
Earth's axis is called the polar axis. The perpendicular axis is called the declination axis. If an astronomer locks the declination axis in place after the telescope is pointed
at an object of interest, a small motor can drive the telescope slowly around its polar axis, following the motion of the object in the sky as Earth turns. Equatorial
mounts are expensive and complicated. Newer telescopes often stand on simpler, less expensive mounts and rely on computers to control the motor and position the
telescope correctly.
Modern astronomers seldom actually look through a telescope eyepiece. Instead they operate the telescope and dome from comfortable control rooms--or even
remotely from their offices far away from the observatory--where computers and video screens show exactly what happens at all times.

B

Equipment for Different Wavelengths

The visible light viewed through optical telescopes is just one part of the electromagnetic spectrum, the range of electric and magnetic waves that spans radio waves,
visible light, X rays, and all the types of radiation in between. Astronomers are also interested in observing electromagnetic waves with wavelengths longer or shorter
than those of visible light. These waves, invisible to the human eye, are also invisible to the telescopes designed to gather visible light, so astronomers need special
telescopes and detectors to study the rest of the spectrum. See also Electromagnetic Radiation.
The coldest objects in the universe emit radio waves. Radio waves have the longest wavelength of any electromagnetic waves. Astronomers use instruments called radio
telescopes to gather and study radio waves that come from space. Radio telescopes are usually huge metal dishes, set into the ground or perched on supports above
the ground. Radio waves from space hit the dish and bounce off. The dish is shaped in such a way that the radio waves bounce off to a single point above the dish, no
matter where they first hit the dish. Detectors at this point, called the focal point, send the signals to computers that process the information. The largest radio
telescope is at Arecibo Observatory in Puerto Rico. The Arecibo radio telescope is set in a natural depression in the earth and measures 305 m (1,000 ft) across. See
also Radio Astronomy.
On the electromagnetic spectrum, infrared radiation falls between radio waves and visible light. Most ...


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