Astronomy is a natural science which is the study of celestial objects such as stars, galaxies, planets, moons, asteroids, comets and nebulae, the physics, chemistry, and evolution of such objects, and phenomena that originate outside the atmosphere of Earth, including supernovae explosions, gamma ray bursts, and cosmic microwave background radiation. A related but distinct subject, cosmology, is concerned with studying the universe as a whole. Astronomy is one of the oldest sciences. The early civilizations in recorded history, such as the Babylonians, Greeks, Indians, Egyptians, Nubians, Iranians, Chinese, and Maya performed methodical observations of the night sky. However, the invention of the telescope was required before astronomy was able to develop into a modern science. Historically, astronomy has included disciplines as diverse as astrometry, celestial navigation, observational astronomy and the making of calendars, but professional astronomy is nowadays often considered to be synonymous with astrophysics.

Specific Astronomy subfields are: Radio Astronomy studies radiation with wavelengths greater than approximately one millimeter. Radio astronomy is different from most other forms of observational astronomy in that the observed radio waves can be treated as waves rather than as discrete photons. Hence, it is relatively easier to measure both the amplitude and phase of radio waves, whereas this is not as easily done at shorter wavelengths. Historically, Optical Astronomy, also called visible light astronomy, is the oldest form of astronomy. Optical images of observations were originally drawn by hand. In the late 19th century and most of the 20th century, images were made using photographic equipment. Modern images are made using digital detectors, particularly detectors using charge-coupled devices (CCDs) and recorded on modern medium.

Infrared Astronomy is founded on the detection and analysis of infrared radiation (wavelengths longer than red light). The infrared spectrum is useful for studying objects that are too cold to radiate visible light, such as planets, circumstellar disks or nebulae whose light is blocked by dust. Longer infrared wavelengths can penetrate clouds of dust that block visible light, allowing the observation of young stars in molecular clouds and the cores of galaxies. Ultraviolet Astronomy refers to observations at ultraviolet wavelengths between approximately 100 and 3200 (10 to 320 nm). Light at these wavelengths is absorbed by the Earth's atmosphere, so observations at these wavelengths must be performed from the upper atmosphere or from space. X-ray Astronomy is the study of astronomical objects at X-ray wavelengths. Typically, X-ray radiation is produced by synchrotron emission (the result of electrons orbiting magnetic field lines), thermal emission from thin gases above 107 kelvins, and thermal emission from thick gases above 107 Kelvin. Since X-rays are absorbed by the Earth's atmosphere, all X-ray observations must be performed from high-altitude balloons, rockets, or spacecraft. Gamma Ray Astronomy is the study of astronomical objects at the shortest wavelengths of the electromagnetic spectrum.

Photos on this website courtesy of:

Jet Propulsion Laboratory     European Space Agency     National Science Foundation
Space Telescope Science Institute     National Aeronautics and Space Administration
National Solar Observatory     National Optical Astronomy Observatory
California Institute of Technology     US Naval Research Lab     Solar Dynamics Observatory

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