Astronomy is a natural science that studies celestial objects and phenomena.
It applies mathematics, physics, and chemistry, in an effort to explain the origin of those objects and phenomena and their evolution.
Objects of interest include planets, moons, stars, galaxies, and comets; the phenomena include supernova explosions, gamma-ray bursts, and cosmic microwave background radiation.
More generally, all phenomena that originate outside Earth’s atmosphere are within the purview of astronomy. A related but distinct subject, physical cosmology, is concerned with the study of the Universe as a whole.
Astronomy is one of the oldest of the natural sciences.
The early civilizations in recorded history, such as the Babylonians, Greeks, Indians, Egyptians, Nubians, Iranians, Chinese, Maya, and many ancient indigenous peoples of the Americas performed methodical observations of the night sky.
Historically, astronomy has included disciplines as diverse as astrometry, celestial navigation, observational astronomy, and the making of calendars, but professional astronomy is now often considered to be synonymous with astrophysics.
Professional astronomy is 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 observational results and observations being used to confirm theoretical results.
Astronomy is one of the few sciences in which amateurs still play an active role, especially in the discovery and observation of transient events.
Amateur astronomers have made and contributed to many important astronomical discoveries, such as finding new comets.
In early times, astronomy only comprised the observation and predictions of the motions of objects visible to the naked eye.
In some locations, early cultures assembled massive artifacts that possibly had some astronomical purpose. In addition to their ceremonial uses, these observatories could be employed to determine the seasons, an important factor in knowing when to plant crops, as well as in understanding the length of the year.
Before tools such as the telescope were invented, early study of the stars was conducted using the naked eye. As civilizations developed, most notably in Mesopotamia, Greece, Persia, India, China, Egypt, and Central America, astronomical observatories were assembled, and ideas on the nature of the Universe began to be explored.
Most of the early astronomy actually consisted of mapping the positions of the stars and planets, a science now referred to as astrometry.
The Earth was believed to be the center of the Universe with the Sun, the Moon and the stars rotating around it. This is known as the geocentric model of the Universe, or the Ptolemaic system, named after Ptolemy.
A particularly important early development was the beginning of mathematical and scientific astronomy, which began among the Babylonians, who laid the foundations for the later astronomical traditions that developed in many other civilizations. The Babylonians discovered that lunar eclipses recurred in a repeating cycle known as a saros.
Following the Babylonians, significant advances in astronomy were made in ancient Greece and the Hellenistic world. Greek astronomy is characterized from the start by seeking a rational, physical explanation for celestial phenomena.
In the 3rd century BC, Aristarchus of Samos estimated the size and distance of the Moon and Sun, and he proposed a heliocentric model of the solar system.
In the 2nd century BC, Hipparchus discovered precession, calculated the size and distance of the Moon and invented the earliest known astronomical devices such as the astrolabe.
Hipparchus also created a comprehensive catalog of 1020 stars, and most of the constellations of the northern hemisphere derive from Greek astronomy.
The Antikythera mechanism (c. 150–80 BC) was an early analog computer designed to calculate the location of the Sun, Moon, and planets for a given date.
Technological artifacts of similar complexity did not reappear until the 14th century when mechanical astronomical clocks appeared in Europe.
During the Middle Ages, astronomy was mostly stagnant in medieval Europe, at least until the 13th century.
However, astronomy flourished in the Islamic world and other parts of the world. This led to the emergence of the first astronomical observatories in the Muslim world by the early 9th century.
In 964, the Andromeda Galaxy, the largest galaxy in the Local Group, was described by the Persian astronomer Azophi in his Book of Fixed Stars.
The SN 1006 supernova, the brightest apparent magnitude stellar event in recorded history, was observed by the Egyptian Arabic astronomer Ali ibn Ridwan and the Chinese astronomers in 1006.
Some of the prominent Islamic (mostly Persian and Arab) astronomers who made significant contributions to the science include Al-Battani, Thebit, Azophi, Albumasar, Biruni, Arzachel, Al-Birjandi, and the astronomers of the Maragheh and Samarkand observatories. Astronomers during that time introduced many Arabic names now used for individual stars
It is also believed that the ruins at Great Zimbabwe and Timbuktu may have housed an astronomical observatory.
Europeans had previously believed that there had been no astronomical observation in pre-colonial Middle Ages sub-Saharan Africa but modern discoveries show otherwise.
The Roman Catholic Church gave more financial and social support to the study of astronomy for over six centuries, from the recovery of ancient learning during the late Middle Ages into the Enlightenment, than any other, and, probably, all other, institutions. Among the Church’s motives was finding the date for Easter.
Galileo’s sketches and observations of the Moon revealed that the surface was mountainous.
During the Renaissance, Nicolaus Copernicus proposed a heliocentric model of the solar system. His work was defended by Galileo Galilei and expanded upon by Johannes Kepler.
Kepler was the first to devise a system that described correctly the details of the motion of the planets with the Sun at the center. However, Kepler did not succeed in formulating a theory behind the laws he wrote down.
It was left to Newton’s invention of celestial dynamics and his law of gravitation to finally explain the motions of the planets. Newton also developed the reflecting telescope.
The English astronomer John Flamsteed cataloged over 3000 stars. Further discoveries paralleled the improvements in the size and quality of the telescope. More extensive star catalogs were produced by Lacaille.
The astronomer William Herschel made a detailed catalog of nebulosity and clusters, and in 1781 discovered the planet Uranus, the first new planet found. The distance to a star was announced in 1838 when the parallax of 61 Cygni was measured by Friedrich Bessel.
During the 18–19th centuries, the study of the three-body problem by Euler, Clairaut, and D’Alembert led to more accurate predictions about the motions of the Moon and planets.
This work was further refined by Lagrange and Laplace, allowing the masses of the planets and moons to be estimated from their perturbations.
Significant advances in astronomy came about with the introduction of new technology, including the spectroscope and photography.
Fraunhofer discovered about 600 bands in the spectrum of the Sun in 1814–15, which, in 1859, Kirchhoff ascribed to the presence of different elements. Stars were proven to be similar to the Earth’s own Sun, but with a wide range of temperatures, masses, and sizes.
The existence of the Earth’s galaxy, the Milky Way, as a separate group of stars, was only proved in the 20th century, along with the existence of “external” galaxies.
The observed recession of those galaxies led to the discovery of the expansion of the Universe. Theoretical astronomy led to speculations on the existence of objects such as black holes and neutron stars, which have been used to explain such observed phenomena as quasars, pulsars, blazars, and radio galaxies.
Physical cosmology made huge advances during the 20th century, with the model of the Big Bang, which is heavily supported by evidence provided by cosmic microwave background radiation, Hubble’s law, and the cosmological abundances of elements.
Space telescopes have enabled measurements in parts of the electromagnetic spectrum normally blocked or blurred by the atmosphere.
In February 2016, it was revealed that the LIGO project had detected evidence of gravitational waves in the previous September.
*This article was originally published at en.wikipedia.org.