Page 30 - Life beyond the Karman

Radar
Radar is an electromagnetic sensor used to detect, locate, track, and recognise objects of various kinds at considerable distances. It operates by transmitting electromagnetic energy towards objects, commonly referred to as targets, and observing the echoes returned from them.
The targets may be aircraft, ships, spacecraft, automotive vehicles, and astronomical bodies, or even birds, insects, and rain.
Besides determining the presence, location, and velocity of such objects, radar can sometimes also obtain their size and shape. What distinguishes radar from optical and infrared sensing devices is its ability to detect faraway objects under adverse weather conditions and to determine their range, or distance, with precision.
Radiation
Radiation is a flow of atomic and subatomic particles and waves, such as those that characterize heat rays, light rays, and X rays. All matter is constantly bombarded with radiation of all types from cosmic and terrestrial sources.
Collecting waves
Radio waves make it through Earth’s atmosphere and can be detected at the surface. Light also makes it through but is best collected at mountain-top sites, along with infra-red waves. Other wavelengths do not get through and must be collected by telescopes in space.
X-Ray Images
Even if astronomers can see an object in visible light and radio waves, they might also take a picture using X-rays because an X-ray image can reveal its hotter, higher-energy features. This image is of the same object as the one made using radio waves.
The electromagnetic spectrum
The full range of energy waves given off by objects in space is known as the electromagnetic spectrum. The various wavelengths reveal different aspects of the universe. Gamma rays have identified far distant, exploding stars, and X-rays have shown the location of black holes. Ultraviolet energy is given off by the hottest stars, infrared waves reveal newly-born stars normally hidden by dust, and radio waves have provided evidence for the big bang.
Electromagnetic radiation is a form of energy that spreads through empty space at the speed of light. It travels in the form of individual “wave-packets”, called photons. The smaller the waves in the packet, the more energy the photon carries. The electromagnetic spectrum is the full range of wavelengths that photons can carry, ranging from low-energy radio with long waves to the shortest wavelengths.
Radio images
The cooler parts of stars, gases, and galaxies all send out radio waves. Astronomers can detect and “map” large structures, such as the remains of an exploded star, using their radio telescopes. Radio waves from the sun warn us when it is about to get active.
Radar Screen X-Ray Telescope Electromagnetic Spectrum
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LIFE BEYOND THE KÁRMÁN LINE - OUTER SPACE