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The Astronomer, 1668, by Johannes Vermeer JohannesVermeer-TheAstronomer(1668).jpg
The Astronomer , 1668, by Johannes Vermeer

An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, moons, comets and galaxies – in either observational (by analyzing the data) or theoretical astronomy. Examples of topics or fields astronomers study include planetary science, solar astronomy, the origin or evolution of stars, or the formation of galaxies. Related but distinct subjects like physical cosmology, which studies the Universe as a whole.



Astronomers usually fall under either of two main types: observational and theoretical. Observational astronomers make direct observations of celestial objects and analyze the data. In contrast, theoretical astronomers create and investigate models of things that cannot be observed. Because it takes millions to billions of years for a system of stars or a galaxy to complete a life cycle, astronomers must observe snapshots of different systems at unique points in their evolution to determine how they form, evolve, and die. They use these data to create models or simulations to theorize how different celestial objects work.

Further subcategories under these two main branches of astronomy include planetary astronomy, galactic astronomy, or physical cosmology.


Galileo is often referred to as the Father of modern astronomy, portrait by Justus Sustermans Justus Sustermans - Portrait of Galileo Galilei (Uffizi).jpg
Galileo is often referred to as the Father of modern astronomy, portrait by Justus Sustermans

Historically, astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using physical laws. Today, that distinction has mostly disappeared and the terms "astronomer" and "astrophysicist" are interchangeable. Professional astronomers are highly educated individuals who typically have a PhD in physics or astronomy and are employed by research institutions or universities. [1] They spend the majority of their time working on research, although they quite often have other duties such as teaching, building instruments, or aiding in the operation of an observatory.

The American Astronomical Society, which is the major organization of professional astronomers in North America, has approximately 7,000 members. This number includes scientists from other fields such as physics, geology, and engineering, whose research interests are closely related to astronomy. [2] The International Astronomical Union comprises almost 10,145 members from 70 different countries who are involved in astronomical research at the PhD level and beyond. [3]

Portrait of the Flemish astronomer Ferdinand Verbiest who became Head of the Mathematical Board and Director of the Observatory of the Chinese emperor in 1669 Nan Gong Huai Ren Xiang .jpg
Portrait of the Flemish astronomer Ferdinand Verbiest who became Head of the Mathematical Board and Director of the Observatory of the Chinese emperor in 1669

Contrary to the classical image of an old astronomer peering through a telescope through the dark hours of the night, it is far more common to use a charge-coupled device (CCD) camera to record a long, deep exposure, allowing a more sensitive image to be created because the light is added over time. Before CCDs, photographic plates were a common method of observation. Modern astronomers spend relatively little time at telescopes usually just a few weeks per year. Analysis of observed phenomena, along with making predictions as to the causes of what they observe, takes the majority of observational astronomers' time.

Astronomers who serve as faculty spend much of their time teaching undergraduate and graduate classes. Most universities also have outreach programs including public telescope time and sometimes planetariums as a public service to encourage interest in the field.

Those who become astronomers usually have a broad background in maths, sciences and computing in high school. Taking courses that teach how to research, write and present papers are also invaluable. In college/university most astronomers get a PhD in astronomy or physics.

Amateur astronomers

While there is a relatively low number of professional astronomers, the field is popular among amateurs. Most cities have amateur astronomy clubs that meet on a regular basis and often host star parties. The Astronomical Society of the Pacific is the largest general astronomical society in the world, comprising both professional and amateur astronomers as well as educators from 70 different nations. [4] Like any hobby, most people who think of themselves as amateur astronomers may devote a few hours a month to stargazing and reading the latest developments in research. However, amateurs span the range from so-called "armchair astronomers" to the very ambitious, who own science-grade telescopes and instruments with which they are able to make their own discoveries and assist professional astronomers in research.

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Amateur astronomy Hobby of watching the sky and stars

Amateur astronomy is a hobby where participants enjoy observing or imaging celestial objects in the sky using the unaided eye, binoculars, or telescopes. Even though scientific research may not be their primary goal, some amateur astronomers make contributions in doing citizen science, such as by monitoring variable stars, double stars, sunspots, or occultations of stars by the Moon or asteroids, or by discovering transient astronomical events, such as comets, galactic novae or supernovae in other galaxies.

Astronomy is the oldest of the natural sciences, dating back to antiquity, with its origins in the religious, mythological, cosmological, calendrical, and astrological beliefs and practices of prehistory: vestiges of these are still found in astrology, a discipline long interwoven with public and governmental astronomy. It was not completely separated in Europe during the Copernican Revolution starting in 1543. In some cultures, astronomical data was used for astrological prognostication. The study of astronomy has received financial and social support from many institutions, especially the Church, which was its largest source of support between the 12th century to the Enlightenment.

Astronomy Scientific study of celestial objects and phenomena

Astronomy is a natural science that studies celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and evolution. Objects of interest include planets, moons, stars, nebulae, galaxies, and comets. Relevant phenomena include supernova explosions, gamma ray bursts, quasars, blazars, pulsars, and cosmic microwave background radiation. More generally, astronomy studies everything that originates beyond Earth's atmosphere. Cosmology is a branch of astronomy that studies the universe as a whole.

Radio astronomy subfield of astronomy that studies celestial objects at radio frequencies

Radio astronomy is a subfield of astronomy that studies celestial objects at radio frequencies. The first detection of radio waves from an astronomical object was in 1932, when Karl Jansky at Bell Telephone Laboratories observed radiation coming from the Milky Way. Subsequent observations have identified a number of different sources of radio emission. These include stars and galaxies, as well as entirely new classes of objects, such as radio galaxies, quasars, pulsars, and masers. The discovery of the cosmic microwave background radiation, regarded as evidence for the Big Bang theory, was made through radio astronomy.

Sandra Faber Astrophysicist

Sandra Moore Faber is an astrophysicist known for her research on the evolution of galaxies. She is the University Professor of Astronomy and Astrophysics at the University of California, Santa Cruz, and works at the Lick Observatory. She has made important discoveries linking the brightness of galaxies to the speed of stars within them and was the co-discoverer of the Faber–Jackson relation. Faber was also instrumental in designing the Keck telescopes in Hawaii.

Photometry (astronomy) Determination of light intensities of astronomical bodies

Photometry, from Greek photo- ("light") and -metry ("measure"), is a technique used in astronomy that is concerned with measuring the flux or intensity of light radiated by astronomical objects. This light is measured through a telescope using a photometer, often made using electronic devices such as a CCD photometer or a photoelectric photometer that converts light into an electric current by the photoelectric effect. When calibrated against standard stars of known intensity and colour, photometers can measure the brightness or apparent magnitude of celestial objects.

American Astronomical Society Society of professional astronomers

The American Astronomical Society is an American society of professional astronomers and other interested individuals, headquartered in Washington, DC. The primary objective of the AAS is to promote the advancement of astronomy and closely related branches of science, while the secondary purpose includes enhancing astronomy education and providing a political voice for its members through lobbying and grassroots activities. Its current mission is to enhance and share humanity's scientific understanding of the universe.

Astrophysics is a science that employs the methods and principles of physics in the study of astronomical objects and phenomena. Among the subjects studied are the Sun, other stars, galaxies, extrasolar planets, the interstellar medium and the cosmic microwave background. Emissions from these objects are examined across all parts of the electromagnetic spectrum, and the properties examined include luminosity, density, temperature, and chemical composition. Because astrophysics is a very broad subject, astrophysicists apply concepts and methods from many disciplines of physics, including classical mechanics, electromagnetism, statistical mechanics, thermodynamics, quantum mechanics, relativity, nuclear and particle physics, and atomic and molecular physics.

Observational astronomy Division of astronomy

Observational astronomy is a division of astronomy that is concerned with recording data about the observable universe, in contrast with theoretical astronomy, which is mainly concerned with calculating the measurable implications of physical models. It is the practice and study of observing celestial objects with the use of telescopes and other astronomical instruments.

Deep-sky object

A deep-sky object (DSO) is any astronomical object that is not an individual star or Solar System object. The classification is used for the most part by amateur astronomers to denote visually observed faint naked eye and telescopic objects such as star clusters, nebulae and galaxies. This distinction is practical and technical, implying a variety of instruments and techniques appropriate to observation, and does not distinguish the nature of the object itself.

Institute of Astronomy, Cambridge

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Theoretical astronomy is the use of analytical and computational models based on principles from physics and chemistry to describe and explain astronomical objects and astronomical phenomena. Theorists in astronomy endeavor to create theoretical models and from the results predict observational consequences of those models. The observation of a phenomenon predicted by a model allows astronomers to select between several alternate or conflicting models as the one best able to describe the phenomena.

International Year of Astronomy

The International Year of Astronomy (IYA2009) was a year-long celebration of astronomy that took place in 2009 to coincide with the 400th anniversary of the first recorded astronomical observations with a telescope by Galileo Galilei and the publication of Johannes Kepler's Astronomia nova in the 17th century. The Year was declared by the 62nd General Assembly of the United Nations. A global scheme, laid out by the International Astronomical Union (IAU), was also endorsed by UNESCO, the UN body responsible for educational, scientific, and cultural matters.

A transient astronomical event, often shortened by astronomers to a transient, is an astronomical object or phenomenon whose duration may be from milliseconds to days, weeks, or even several years. This is in contrast to the timescale of the millions or billions of years during which the galaxies and their component stars in our universe have evolved. Singularly, the term is used for violent deep-sky events, such as supernovae, novae, dwarf nova outbursts, gamma-ray bursts, and tidal disruption events, as well as gravitational microlensing, transits, eclipses, and comets. These events are part of the broader topic of time domain astronomy.

Thomas Boles is a Scottish amateur astronomer, discoverer of astronomical objects, author, broadcaster and former communications and computer engineer, who observes from his private "Coddenham Observatory" in Coddenham, Suffolk, United Kingdom. He is known for having discovered a record number of supernovae. The main-belt asteroid 7648 Tomboles is named in his honor.

The Hans A. Bethe Prize, is presented annually by the American Physical Society. The prize honors outstanding work in theory, experiment or observation in the areas of astrophysics, nuclear physics, nuclear astrophysics, or closely related fields. The prize consists of $10,000 and a certificate citing the contributions made by the recipient.

Smadar Naoz Israeli-American astrophysicist

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Ajit Kembhavi

Ajit Kembhavi is an Indian astrophysicist. He is presently a Professor Emeritus at the Inter-University Centre for Astronomy and Astrophysics, (IUCAA) at Pune, India, of which he was also a founder member. He also serves as a Vice President of the International Astronomical Union.


  1. "Frequently Asked Questions About Becoming an Astronomer". NOAO. Archived from the original on 3 April 2009. Retrieved 29 March 2009.
  2. "American Astronomical Society Home". AAS. Archived from the original on 2 August 2009. Retrieved 14 August 2009.
  3. "About IAU". IAU. Retrieved 14 August 2009.
  4. "About Us". Astronomical Society of the Pacific. Archived from the original on 25 February 2009. Retrieved 29 March 2009.