Astronomy is the science dealing with all the celestial objects in the universe, including the planets and their satellites (e.g. our Earth and the moon), comets and meteors, the stars (including our sun), and interstellar matter, the star systems known as galaxies, and clusters of galaxies.
Ancient peoples watched the stars and memorised their positions relative to each other by visualising constellations – shapes which suggested to them mythical figures. If a new star appeared its position was noted on a star map. The first comet was recorded this way, over 2,000 years ago. Today, astronomers use telescopes (optical, radio, and others) to study stars, planets, and galaxies.
Astronomers are scientists who study all the objects in the universe, such as stars, planets, and Galaxies. They use ground-based telescopes of many kinds, launch space probes that visit the other planets in the solar system, and send satellites into space to study the universe from high above the Earth‘s atmosphere.
Astronomy analyses the radiation received on Earth or its vicinity, from the constituent parts of the Universe. For most of man’s history, the visible part of the electromagnetic spectrum was the sole medium used for astronomical observation, and the human eye was the only receiver. The invention of the optical telescope greatly enhanced our view of the night sky, revealing spectacular details of the Moon and planets, and masses of previously unseen stars and nebulae.
Instruments such as photometers (which measure light intensity) and spectrometers (which split light into its spectrum, or constituent colors), have made the physical study of stars possible, leading to knowledge of their nature, structure, and evolution. These instruments, and photographic plates and electronic imaging devices (e.g. charge-coupled detectors, or CCDs – now used in the consumer market such as in digital cameras) have made possible the field known as astrophysics – the aplication of physics to astronomy, and have extended the range of the accessible spectrum outside the visible portion.
Astronomers are no longer limited to the visible or near-visible spectrum. Radio telescopes, invented in the 1930s, and the discoveries they made have revolutionised astronomy, and thanks to space technology, we now have access to the whole electromagnetic spectrum, as well as particles from the Sun and other objects. Spacecraft carry telescopes and other astronomical instruments above the Earth’s atmosphere, and to other planets in our solar system. This has created whole new branches of astronomy such as X-ray and Gamma-ray astronomy.
Astronomy is a natural science that is the study of celestial objects (such as moons, planets, stars, nebulae, and galaxies), the physics,chemistry, mathematics, and evolution of such objects, and phenomena that originate outside the atmosphere of Earth, including supernovae explosions, gamma ray bursts, and cosmic background radiation. A related but distinct subject, cosmology, is concerned with studying the universe as a whole.
Astronomy is one of the oldest sciences. Prehistoric cultures left behind astronomical artifacts such as the Egyptian monuments and Nubian monuments, and early civilizations such as the Babylonians, Greeks, Chinese, Indians, Iranians 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.
During the 20th century, the field of professional astronomy split into observational and theoretical branches. Observational astronomy is focused on acquiring data from observations of astronomical objects, which is then analyzed using basic principles of physics. Theoretical astronomy is oriented toward the development of computer or analytical models to describe astronomical objects and phenomena. The two fields complement each other, with theoretical astronomy seeking to explain the observational results and observations being used to confirm theoretical results.
Amateur astronomers have contributed to many important astronomical discoveries, and astronomy is one of the few sciences where amateurs can still play an active role, especially in the discovery and observation of transient phenomena.