Telescopes from the Ground Up

Dishing it out

Get to the root of it

Today’s radio telescopes use parabolic reflectors, called dishes, to collect radio waves. These dishes are the same shape as the mirrors in reflecting telescopes that study visible light, and work the same way. Radio waves bounce off the dish and meet at a single point, the focal point, where a receiver has been carefully positioned to capture them.

These receivers are similar to the ones found in car radios. The receivers record information, just as a camera or a charge-coupled device (CCD) would in other types of telescopes. Since the incoming waves are faint, the receiver amplifies them before sending the signal to a computer that stores the data.

Radio waves, 24-7

In some ways, radio astronomers have an easier time than optical astronomers.

Both radio and visible light share the ability to escape atmospheric absorption. They pass through Earth’s atmosphere and reach the ground, where they can be detected by ground-based telescopes. That is where their similarity ends, however.

Get to the root of it

Optical astronomers can only observe their targets at night, since bright sunlight overwhelms faint starlight. Radio astronomers, however, have the option of looking for radio sources during the day, since the Sun gives off radio waves only weakly.

In addition, optical astronomers can only make observations in clear weather, since visible light is mostly absorbed by clouds. Radio astronomers, on the other hand, enjoy observing during cloudy, even stormy, weather, because radio waves pass through clouds as if they weren’t there.

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