The Invisible Universe
Most of our knowledge about the universe comes from what we can see, but visible light is only a small part of the electromagnetic spectrum. Astronomical objects such as stars, galaxies, gas, gust and energetic particles also emit natural radio signals, and like natural light, they pass through Earth’s atmosphere without being absorbed. In 1932, Karl Jansky first discovered radio waves coming from the sky, and in 1937 Grote Reber, a radio engineer and amateur astronomer, built the first radio telescope. It was an iron dish 9 m in diameter, designed to capture cosmic radio emissions and direct them towards a receiver. From these invisible emissions, radio astronomers can build images—but the signals are weak after travelling billions of kilometres, and man-made radio signals can easily interfere with their cosmic counterparts and contaminate data. Radio telescopes are therefore built in remote areas so they can “hear” the universe more clearly and investigate phenomenon invisible to us through telescopes. Radio astronomers study black holes at the hearts of galaxies, the dust-shrouded regions where stars and planets are born, and even the Cosmic Microwave Background Radiation left over from the Big Bang—the birth patterns of the universe.