telescopes

an instrument that collects electromagnetic radiation from the sky and concentrates it for better observation 

 Refracting Telescopes

Telescopes that use lenses to gather and focus light are called refracting telescopes.  A refracting telescope has an objective lens that bends light that passes through it and focuses the light to be magnified by an eyepiece. Refracting telescopes have two disadvantages. First, lenses focus different colors of light at slightly different distances, so images cannot be perfectly focused. Second, the size of a refracting telescope is also limited by the size of the objective lens. If the lens is too large, the glass sags under its own weight and images are distorted. These limitations are two reasons that most professional astronomers use reflecting telescopes.

Reflecting Telescopes

A telescope that uses a curved mirror to gather and focus light is called a reflecting telescope. Light enters the telescope and is reflected from a large, curved mirror to a flat mirror. The flat mirror focuses the image and reflects the light to be magnified by the eyepiece.

One advantage of reflecting telescopes is that the mirrors can be very large. Large mirrors allow reflecting telescopes to gather more light than refracting telescopes do. Another advantage is that curved mirrors are polished on their curved side, which prevents light from entering the glass. Thus, any flaws in the glass do not affect the light. A third advantage is that mirrors can focus all colors of light to the same focal point. Therefore, reflecting telescopes allow all colors of light from an object to be seen in focus at the same time.

 

Large reflectig telescope

the lage telescope is controled by a computer and easy to take digital piture that are mor acurate than human drawing. 

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Optical Telescopes and the Atmosphere

 
The light gathered by telescopes on the Earth is affected by the atmosphere. The Earth’s atmosphere causes starlight to shimmer and blur due to the motion of the air above the telescope. Also, light pollution from large cities can make the sky look bright. As a result, an observer’s ability to view faint objects is limited. Astronomers often place telescopes in dry areas to avoid moisture in the air. Mountaintops are also good locations for telescopes because the air is thinner at higher elevations. In addition, mountaintops generally have less air pollution and light pollution than other areas do.

 they are also in space to avoide problems from our admosphear 

 

 Nonoptical Telescopes

 study invisible radiation, scientists use nonoptical telescopes. Nonoptical telescopes detect radiation that cannot be seen by the human eye. Astronomers study the entire electromagnetic spectrum because each type of radiation reveals different clues about an object. Our galaxy looks very different when it is observed at various wavelengths. A different type of telescope was used to produce each image. The “cloud” that goes across the image is the Milky Way galaxy. 

 

 

Radio Telescopes

Radio telescopes detect radio waves. Radio telescopes have to be much larger than optical telescopes because radio wavelengths are about 1 million times longer than optical wavelengths. Most radio radiation reaches the ground and can be detected both during the day and night. The surface of radio telescopes does not have to be as flawless as the lenses and mirrors of optical telescopes. In fact, the surface of a radio telescope does not have to be solid.

 

 
 
Linking Radio Telescopes
 Astronomers can get more detailed images of the universe by linking radio telescopes together. When radio telescopes are linked together, they work like a single giant telescope. For example, the Very Large Array (VLA) consists of 27 radio telescopes that are spread over 30 km. Working together, the telescopes function as a single telescope that is 30 km across!
 
 

Nonoptical Telescopes in Space
Because most electromagnetic waves are blocked by the Earth’s atmosphere, scientists have placed ultraviolet telescopes, infrared telescopes, gamma-ray telescopes, and X-ray telescopes in space. The Chandra X-Ray Observatory, a space-based telescope that detects X rays. X-ray telescopes in space can be much more sensitive than optical telescopes. For example, NASA has tested an X-ray telescope that can detect an object that is the size of a frisbee on the surface of the sun. If an optical telescope had a similar power, it could detect a hair on the head of an astronaut on the moon!
 
 

 

Photo Gallery: telescopes

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