Astronomy is one of the oldest sciences. Astronomers of early astrometry, celestial navigation, observational astronomy, the making of calendars, and even astrology, but professional astronomy is nowadays often considered to be synonymous with astrophysics.

Since the 20th century, the field of professional astronomy split into observational used to confirm theoretical results.

Amateur astronomers active role, especially in the discovery and observation of transient phenomena.

Old or even ancient astronomy is not to be confused with astrology, the belief system which claims that human affairs are correlated with the positions of celestial objects. Although the two fields share a common origin and a part of their methods (namely, the use of ephemerides), they are distinct.

2009 has been declared by the UN to be the International Year of Astronomy 2009 (IYA2009). The focus is on enhancing the public’s understanding and engagement with astronomy.

Contents

• 1.1 Use of terms "astronomy" and "astrophysics"
• 2.1 Scientific revolution
• 3.1 Radio astronomy
• 3.2 Infrared astronomy
• 3.3 Optical astronomy
• 3.4 Ultraviolet astronomy
• 3.5 X-ray astronomy
• 3.6 Gamma-ray astronomy
• 3.7 Fields not based on the electromagnetic spectrum
• 3.8 Astrometry and celestial mechanics
• 4 Theoretical astronomy
• 5.1 Solar astronomy
• 5.2 Planetary science
• 5.3 Stellar astronomy
• 5.4 Galactic astronomy
• 5.5 Extragalactic astronomy
• 5.6 Cosmology
• 6 Interdisciplinary studies
• 7 Amateur astronomy
• 8 Major questions in astronomy
• 9 The International Year of Astronomy 2009
• 10 See also
• 11 References
• 12 External links

Lexicology

The word astronomy literally means "law of the stars" (or "culture of the stars" depending on the translation) and is derived from the Greek αστρονομία, astronomia, from the words άστρον (astron, "star") and νόμος (nomos, "laws or cultures").

Use of terms "astronomy" and "astrophysics"

Generally, either the term "astronomy" or "astrophysics" may be used to refer to this subject. historically affiliated with a physics department, One of the leading scientific journals in the field is named Astronomy and Astrophysics.

History

In early times, astronomy only comprised the observation and the year.

Before tools such as the telescope were invented early study of the universe.

A number of notable astronomical discoveries were made prior to the application of the telescope. For example, the obliquity of the ecliptic was estimated as early as 1000 BC by Chinese astronomers. The Chaldeans discovered that lunar eclipses recurred in a repeating cycle known as a saros. 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.

The earliest known astronomical device was the Antikythera mechanism, an ancient Greek 150-80 BC, and was the earliest ancestor of an astronomical analog computer. Similar astronomical analog computing devices were later constructed by Arabic astronomers and then European astronomers.

During the Middle Ages, observational astronomy was mostly stagnant in medieval Europe, at least until the 13th century. However, astronomy flourished in the Islamic world discoveries show otherwise.

Scientific revolution

During the Renaissance, Nicolaus Copernicus proposed a heliocentric model of the solar system. His work was defended, expanded upon, and corrected by Galileo Galilei and Johannes Kepler. Galileo innovated by using telescopes to enhance his observations.

Kepler was the first to devise a system that described correctly the 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.

Further discoveries paralleled the improvements in the size and 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 first announced in 1838 when the parallax of 61 Cygni was measured by Friedrich Bessel.

During the nineteenth century, attention to 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 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 black holes and neutron stars. Physical cosmology made huge advances during the 20th century, with the model of the Big Bang heavily supported by the evidence provided by astronomy and physics, such as the cosmic microwave background radiation, Hubble's law, and cosmological abundances of elements.

Observational astronomy

In astronomy, information is mainly received from the detection and analysis of visible light or other regions of the electromagnetic radiation. Observational astronomy may be divided according to the observed region of the electromagnetic spectrum. Some parts of the spectrum can be observed from the Earth's below.

Radio astronomy

Radio astronomy studies radiation with wavelengths greater than approximately one millimeter.

Though some radio waves are produced by astronomical objects in the form of thermal emission, most of the radio emission that is observed from Earth is seen in the form of synchrotron radiation, which is produced when electrons oscillate around magnetic fields.

A wide variety of objects are observable at radio wavelengths, including supernovae, interstellar gas, pulsars, and active galactic nuclei.

Infrared astronomy

Infrared astronomy deals with the detection and analysis of infrared to study chemistry in space, as well as detecting water in comets.

Optical astronomy

Historically, optical astronomy, also called visible light astronomy, is the oldest form of astronomy. particularly detectors using charge-coupled devices (CCDs). Although visible light itself extends from approximately 4000 Å to 7000 Å (400 nm to 700 nm), the same equipment used at these wavelengths is also used to observe some near-ultraviolet and near-infrared radiation.

Ultraviolet astronomy

Ultraviolet astronomy is generally used to refer to observations at ultraviolet wavelengths between approximately 100 and 3200 Å (10 to 320 nm). surveys. Other objects commonly observed in ultraviolet light include planetary nebulae, supernova remnants, and active galactic nuclei.

X-ray astronomy

X-ray astronomy is the study of astronomical objects at X-ray wavelengths. Typically, objects emit X-ray radiation as synchrotron emission (produced by electrons oscillating around magnetic field lines), thermal emission from thin gases (called bremsstrahlung radiation) that is above 10⁷ (10 million) kelvins, and thermal emission from thick gases (called blackbody radiation) that are above 10⁷ Kelvin.

Gamma-ray astronomy

Gamma ray astronomy is the study of astronomical objects at the rays are absorbed by the Earth's atmosphere.

Most gamma-ray emitting sources are actually gamma-ray bursts, pulsars, neutron stars, and black hole candidates such as active galactic nuclei.

Fields not based on the electromagnetic spectrum

Other than electromagnetic radiation, few things may be observed from the Earth that originate from great distances.

In neutrino astronomy, astronomers use special underground facilities such as SAGE, GALLEX, and Kamioka II/III for detecting neutrinos. These neutrinos originate primarily from the Sun but also from supernovae.

Cosmic rays particles.

Gravitational wave astronomy is an emerging new window of astronomy, which aims to use gravitational wave detectors to collect observational data about compact objects. A few observatories have been constructed, such as the Laser Interferometer Gravitational Observatory LIGO, but gravitational waves are extremely difficult to detect.

Planetary astronomy has benefited from direct observation in the direct, laboratory examination.

Astrometry and celestial mechanics

One of the oldest fields in astronomy, and in all of science, is the has been essential in celestial navigation.

Careful measurement of the positions of the planets has led to a solid understanding of gravitational perturbations, and an ability to determine past and future positions of the planets with great accuracy, a field known as celestial mechanics. More recently the tracking of near-Earth objects will allow for predictions of close encounters, and potential collisions, with the Earth.

The measurement of stellar parallax of nearby stars provides a fundamental baseline in the cosmic distance ladder Astrometric results are also used to measure the distribution of dark matter in the galaxy.

During the 1990s, the astrometric technique of measuring the stellar wobble was used to detect large extrasolar planets orbiting nearby stars.

Theoretical astronomy

• Stellar nucleosynthesis
• Big Bang nucleosynthesis
• Supernova nucleosynthesis
• Cosmic ray spallation

• Astrophysics
• Nuclear fusion
  • R-process
  • S-process
• Nuclear fission

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Theoretical astronomers use a wide variety of tools which include analytical models (for example, polytropes to approximate the behaviors of a star) and computational numerical simulations. otherwise not be seen.

Theorists in astronomy endeavor to create theoretical models and between several alternate or conflicting models.

Theorists also try to generate or modify models to take into account abandonment of a model.

Topics studied by theoretical astronomers include: stellar dynamics and evolution; galaxy formation; large-scale structure of matter in the Universe; origin of cosmic rays; general relativity and physical cosmology, including string cosmology and astroparticle physics. in physical phenomena investigated and as the basis for black hole (astro)physics and the study of gravitational waves.

Some widely accepted and studied theories and models in astronomy, now included in the Lambda-CDM model are the Big Bang, Cosmic inflation, dark matter, and fundamental theories of physics.

A few examples of this process:

Dark matter and dark energy are the current leading topics in astronomy, as their discovery and controversy originated during the study of the galaxies.

Specific subfields of astronomy

Solar astronomy

At a distance of about eight light-minutes, the most frequently studied star is the Sun, a typical main-sequence dwarf star of stellar class G2 V, and about 4.6 Gyr in age. The Sun is not considered a variable star, but it does undergo periodic changes in activity known as the sunspot cycle. This is an 11-year fluctuation in sunspot numbers. Sunspots are regions of lower-than- average temperatures that are associated with intense magnetic activity.

The Sun has steadily increased in luminosity over the course of its significant impact on the Earth.

The visible outer surface of the Sun is called the photosphere. Above this layer is a thin region known as the chromosphere. This is surrounded by a transition region of rapidly increasing temperatures, then by the super-heated corona.

At the center of the Sun is the core region, a volume of sufficient temperature and pressure for nuclear fusion to occur. Above the core is the radiation zone, where the plasma conveys the energy flux by means of radiation. The outer layers form a convection zone creates the magnetic activity that generates sun spots.

A solar wind of plasma particles constantly streams outward from the Sun until it reaches the heliopause. This solar wind interacts with the magnetosphere of the Earth to create the Van Allen radiation belts, as well as the aurora where the lines of the Earth's magnetic field descend into the atmosphere.

Planetary science

This astronomical field examines the assemblage of planets, moons, dwarf planets, comets, asteroids, and other bodies orbiting the Sun, as well as extrasolar planets. The solar system discoveries are still being made.

The solar system is subdivided into the inner planets, the asteroid belt, and the outer planets. The inner terrestrial planets consist of Mercury, Venus, Earth, and Mars. The outer gas giant planets are Jupiter, Saturn, Uranus, and Neptune. Beyond Neptune lies the Kuiper Belt, and finally the Oort Cloud, which may extend as far as a light-year.

The planets were formed by a protoplanetary disk of intense bombardment, evidenced by the many impact craters on the Moon. During this period, some of the protoplanets may have collided, the leading hypothesis for how the Moon was formed.

Once a planet reaches sufficient mass, the materials with different densities segregate within, during planetary differentiation. and some planetary cores generate their own magnetic field, which can protect their atmospheres from solar wind stripping.

A planet or moon's interior heat is produced from the collisions that created the body, radioactive materials (e.g. uranium, thorium, and ²⁶Al), or tidal heating. Some planets and moons accumulate enough heat to drive geologic processes such as volcanism and tectonics. Those that accumulate or retain an atmosphere can also undergo surface erosion impact cratering.

Stellar astronomy

The study of stars and stellar evolution understanding; and from computer simulations of the interior.

Star formation occurs in dense regions of dust and gas, known as giant molecular clouds. When destabilized, cloud fragments can collapse under the influence of gravity, to form a protostar. A sufficiently dense, and hot, core region will trigger nuclear fusion, thus creating a main-sequence star.

Almost all elements heavier than hydrogen and helium were created inside the cores of stars.

The characteristics of the resulting star depend primarily upon its phases, as they fuse increasingly heavier elements.

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 form planetary nebulae, and evolve into white dwarfs. The remnant of a supernova is a dense neutron star, or, if the stellar mass was at least three times that of the Sun, a black hole. planetary systems) would be formed from hydrogen and helium alone.

Galactic astronomy

Our solar system orbits within the Milky Way, a barred spiral galaxy that is a prominent member of the Local Group Milky Way that are obscured from view.

In the center of the Milky Way is the core, a bar-shaped bulge with what is believed to be a supermassive black hole younger, population I stars. The disk is surrounded by a spheroid halo of older, population II stars, as well as relatively dense concentrations of stars known as globular clusters.

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. These begin as irregular dark nebulae, which concentrate and collapse (in volumes determined by the Jeans length) to form compact protostars.

As the more massive stars appear, they transform the cloud into an H II region of glowing gas and plasma. The stellar wind and supernova explosions from these stars eventually serve to disperse the cloud, often leaving behind one or more young open clusters of stars. These clusters gradually disperse, and the stars join the population of the Milky Way.

Kinematic studies of matter in the Milky Way and other galaxies have visible matter. A dark matter halo appears to dominate the mass, although the nature of this dark matter remains undetermined.

Extragalactic astronomy

The study of objects outside of our galaxy is a branch of astronomy concerned with the formation and evolution of Galaxies; their morphology and classification; and the examination of active galaxies, and the groups and clusters of galaxies. The latter is important for the understanding of the large-scale structure of the cosmos.

Most galaxies are organized into distinct shapes that allow for classification schemes. They are commonly divided into spiral, elliptical and Irregular galaxies.

As the name suggests, an elliptical galaxy has the cross-sectional shape of an ellipse. The stars move along random clusters, and may be formed through mergers of large galaxies.

A spiral galaxy is organized into a flat, rotating disk, usually surrounded by a halo of older stars. Both the Milky Way and the Andromeda Galaxy are spiral galaxies.

Irregular galaxies are chaotic in appearance, and are neither spiral interaction.

An active galaxy is a formation that is emitting a significant material.

A radio galaxy is an active galaxy that is very luminous in the radio gas. Active galaxies that emit high-energy radiation include Seyfert galaxies, Quasars, and Blazars. Quasars are believed to be the most consistently luminous objects in the known universe.

The large-scale structure of the cosmos organized in a hierarchy of groupings, with the largest being the superclusters. The collective matter is formed into filaments and walls, leaving large voids in between.

Cosmology

Cosmology (from the Greek κοσμος "world, universe" and λογος "word, study") could be considered the study of the universe as a whole.

Observations of the large-scale structure of the universe, a branch known as physical cosmology, of the big bang, wherein our universe began at a single point in time, and thereafter expanded over the course of 13.7 Gyr to its present condition. The concept of the big bang can be traced back to the discovery of the microwave background radiation in 1965.

In the course of this expansion, the universe underwent several the universe experienced a very rapid cosmic inflation, which homogenized the starting conditions. Thereafter, nucleosynthesis produced the elemental abundance of the early universe. (See also nucleocosmochronology.)

When the first atoms formed, space became transparent to radiation, lack of stellar energy sources.

A hierarchical structure of matter began to form from minute extending the cycle.

Gravitational aggregations clustered into filaments, leaving voids and were often organized into groups and clusters of galaxies, then into larger-scale superclusters.

Fundamental to the structure of the universe is the existence of dark matter and dark energy. trying to understand the physics of these components.

Interdisciplinary studies

Astronomy and astrophysics have developed significant interdisciplinary links with other major scientific fields. Archaeoastronomy is the study of ancient or traditional astronomies in their cultural context, utilizing archaeological and anthropological evidence. Astrobiology non-terrestrial life.

The study of chemicals found in space, including their formation, interaction and destruction, is called astrochemistry. These substances are usually found in molecular clouds, although they may also appear in low temperature stars, brown dwarfs and planets. Cosmochemistry is the study of the chemicals found within the Solar System, including the origins of the elements and variations in the isotope ratios. Both of these fields represent an overlap of the disciplines of astronomy and chemistry.

Amateur astronomy

Astronomy is one of the sciences to which amateurs can contribute the most.

Collectively, amateur astronomers observe a variety of celestial objects and phenomena sometimes with equipment that they build themselves. Common targets of amateur astronomers include the Moon, planets, stars, comets, meteor showers, and a variety of deep-sky objects such as star clusters, galaxies, and nebulae. One branch of amateur astronomy, amateur astrophotography, or types of events which interest them.

Most amateurs work at visible wavelengths, but a small minority which are now available to amateurs (e.g. the One-Mile Telescope).

Amateur astronomers continue to make scientific contributions to the astrophotography.

Major questions in astronomy

Although the scientific discipline of astronomy has made tremendous and possibly new developments in theoretical and experimental physics.

• What is the origin of the stellar mass spectrum? That is, why do astronomers observe the same distribution of stellar masses—the initial mass function—apparently regardless of the initial conditions? A deeper understanding of the formation of stars and planets is needed.
• Is there other life in the Universe? Especially, is there other intelligent life? If so, what is the explanation for the Fermi paradox? The existence of life elsewhere has important scientific and philosophical implications.
• What is the nature of dark matter and dark energy? These dominate their true natures.
• Why are the physical constants so finely tuned that they permit the existence of life? Could they be the result of cosmological natural selection? What caused the cosmic inflation that produced our homogeneous universe?
• What will be the ultimate fate of the universe?

The International Year of Astronomy 2009

During the 62nd General Assembly of the UN, 2009 was declared to be the International Year of Astronomy (IYA2009), with the resolution being made official on 20 December 2008. A global scheme laid out by the International Astronomical Union (IAU), it has also been endorsed by UNESCO — the UN towards young people.