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Electromagnetic transmittance, or opacity, of the Earth's atmosphere. Click here for original source URL.

Grote Reber. Click here for original source URL.

Grote Reber's original Radio Antenna. Click here for original source URL.

Replica of Karl Jansky's first radio telescope. Click here for original source URL.

Karl Jansky. Click here for original source URL.

radio telescope is a device that gathers and concentrates radio waves; it is analogous to an optical telescope, which gathers and concentrates light waves. The American engineer Karl Jansky built the first radio telescope at Bell Telephone Labs in 1930. Jansky's radio antenna was 30 meters long, and it rotated on four wheels from a Model T Ford. He used it to detect radio "hiss" from the sky. In the process, he measured radio emission from the Milky Way, towards the constellation Sagittarius. Jansky was sure the hiss was from an astronomical object because it repeated with a cycle of 23 hours and 56 minutes, a sidereal day, whereas a terrestrial source of interference would repeat every 24 hours.

The Arecibo Radio Telescope. Click here for original source URL.

Very Large Array radio telescopes in New Mexico, USA. Click here for original source URL.