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Telescopes from the Ground Up
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Light pollution

Infrared telescopes

Infrared telescopes look for infrared radiation, which human beings perceive as heat. These telescopes must be shielded from all other sources of heat in order to make accurate observations. Because the telescopes themselves emit heat, they are packed with coolants that keep their equipment as chilly as possible.

Radio telescopes

Radio telescopes look for radio waves. They can be used during the day, because the Sun emits radio waves only weakly.

However, radio telescopes encounter light pollution in the form of radio signals from electronics, motors, and transmitters. Signals from cell phones, garage door openers, wireless computer networks, and orbiting satellites can overwhelm the radio signals from space that astronomers are trying to detect.

Communities located near radio telescopes can help reduce radio light pollution by limiting the use of these devices near the telescopes.

Light pollution affects
many kinds of telescopes

Light pollution happens when electromagnetic radiation from man-made sources interferes with our view of objects in the sky. For example, you won’t see many stars if you look up at the night sky from inside a city. This is because the electrical lights around you drown out the light from dimmer stars.

Optical telescopes

We only use optical telescopes, which view visible light, during the night. During the day, the Sun’s dazzling light, scattered by the Earth’s atmosphere, overwhelms the light of the stars.

A similar problem occurs when we try to view the night sky near a city. The glare of city lights drowns out all but the brightest stars. The best optical telescopes are located far away from the light pollution of cities, often on mountaintops.

People can cut down on visible light pollution by turning off unnecessary outdoor lights and using inexpensive shields to direct light toward the ground, not the sky.

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