Scientific study of celestial objects and phenomena
Astronomy (from Greek: ἀστρονομία) is a natural science that studies celestial objects and phenomena. Objects of interest include planets, moons, stars, nebulae, galaxies, and comets; the phenomena also includes supernova explosions, gamma ray bursts, quasars, blazars, pulsars, and cosmic microwave background radiation. A branch of astronomy called cosmology is the study of the Universe as a whole. 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. Most early astronomy consisted of mapping the positions of the stars and planets, a science now referred to as astrometry. Astronomers during that time introduced many Arabic names now used for individual stars. The English astronomer John Flamsteed catalogued over 3000 stars, More extensive star catalogues were produced by Nicolas Louis de Lacaille. 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. Radio astronomy uses radiation with wavelengths greater than approximately one millimeter, outside the visible range. 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. The longer wavelengths of infrared can penetrate clouds of dust that block visible light, allowing the observation of young stars embedded in molecular clouds and the cores of galaxies. Historically, optical astronomy, also called visible light astronomy, is the oldest form of astronomy. Ultraviolet astronomy is best suited to the study of thermal radiation and spectral emission lines from hot blue stars (OB stars) that are very bright in this wave band. This includes the blue stars in other galaxies, which have been the targets of several ultraviolet surveys. X-ray astronomy uses X-ray wavelengths. Notable X-ray sources include X-ray binaries, pulsars, supernova remnants, elliptical galaxies, clusters of galaxies, and active galactic nuclei.
Gamma ray astronomy observes astronomical objects at the shortest wavelengths of the electromagnetic spectrum. These steady gamma-ray emitters include pulsars, neutron stars, and black hole candidates such as active galactic nuclei.
Gravitational-wave astronomy is an emerging field of astronomy that employs gravitational-wave detectors to collect observational data about distant massive objects. Parallax measurements of nearby stars provide an absolute baseline for the properties of more distant stars, as their properties can be compared. During the 1990s, the measurement of the stellar wobble of nearby stars was used to detect large extrasolar planets orbiting those stars.
Theorists in astronomy endeavor to create theoretical models and from the results predict observational consequences of those models. Phenomena modeled by theoretical astronomers include: stellar dynamics and evolution; galaxy formation; large-scale distribution of matter in the Universe; origin of cosmic rays; general relativity and physical cosmology, including string cosmology and astroparticle physics. How the stars shine and how metals formed
The dominant source of energy for massive star.
Dark matter and dark energy are the current leading topics in astronomy, as their discovery and controversy originated during the study of the galaxies.
Among the objects studied are the Sun, other stars, galaxies, extrasolar planets, the interstellar medium and the cosmic microwave background. Matter accumulated in the densest regions, forming clouds of gas and the earliest stars, the Population III stars. These galaxies contain little or no interstellar dust, few star-forming regions, and generally older stars. The arms are dusty regions of star formation within which massive young stars produce a blue tint. Spiral galaxies are typically surrounded by a halo of older stars. Active galaxies that emit shorter frequency, high-energy radiation include Seyfert galaxies, Quasars, and Blazars. This is a region of active star formation that contains many younger, population I stars. Between the stars lies the interstellar medium, a region of sparse matter. In the densest regions, molecular clouds of molecular hydrogen and other elements create star-forming regions. The study of stars and stellar evolution is fundamental to our understanding of the Universe. Star formation occurs in dense regions of dust and gas, known as giant molecular clouds. The characteristics of the resulting star depend primarily upon its starting mass. The final fate of the star depends on its mass, with stars of mass greater than about eight times the Sun becoming core collapse supernovae; while smaller stars blow off their outer layers and leave behind the inert core in the form of a white dwarf. Astronomy and astrophysics have developed significant interdisciplinary links with other major scientific fields. Common targets of amateur astronomers include the Sun, the Moon, planets, stars, comets, meteor showers, and a variety of deep-sky objects such as star clusters, galaxies, and nebulae. They can also discover comets, and perform regular observations of variable stars. A deeper understanding of the formation of stars and planets is needed. How did the first galaxies form?
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