A galaxy is a system of stars, stellar remnants, interstellar gas, dust, and dark matter bound together by gravity. The word is derived from the Greek galaxias (γαλαξίας), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System. Galaxies, averaging an estimated 100 million stars, range in size from dwarfs with less than a thousand stars, to the largest galaxies known – supergiants with one hundred trillion stars, each orbiting its galaxy's center of mass. Most of the mass in a typical galaxy is in the form of dark matter, with only a few percent of that mass visible in the form of stars and nebulae. Supermassive black holes are a common feature at the centres of galaxies.
Astronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry in order to explain their origin and their overall evolution. Objects of interest include planets, moons, stars, nebulae, galaxies, meteoroids, asteroids, 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.
Infrared astronomy is a sub-discipline of astronomy which specializes in the observation and analysis of astronomical objects using infrared (IR) radiation. The wavelength of infrared light ranges from 0.75 to 300 micrometers, and falls in between visible radiation, which ranges from 380 to 750 nanometers, and submillimeter waves.
A galaxy cluster, or a cluster of galaxies, is a structure that consists of anywhere from hundreds to thousands of galaxies that are bound together by gravity, with typical masses ranging from 1014 to 1015 solar masses. They are the second-largest known gravitationally bound structures in the universe after some superclusters (of which only one, the Shapley Supercluster, is known to be bound). They were believed to be the largest known structures in the universe until the 1980s, when superclusters were discovered. One of the key features of clusters is the intracluster medium (ICM). The ICM consists of heated gas between the galaxies and has a peak temperature between 2–15 keV that is dependent on the total mass of the cluster. Galaxy clusters should not be confused with galactic clusters (also known as open clusters), which are star clusters within galaxies, or with globular clusters, which typically orbit galaxies. Small aggregates of galaxies are referred to as galaxy groups rather than clusters of galaxies. The galaxy groups and clusters can themselves cluster together to form superclusters.
Sandra Moore Faber is an American 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 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.
Marc Aaronson was an American astronomer.
The Royal Astronomical Society (RAS) is a learned society and charity that encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. Its headquarters are in Burlington House, on Piccadilly in London. The society has over 4,000 members, known as fellows, most of whom are professional researchers or postgraduate students. Around a quarter of Fellows live outside the UK.
Astrophysics is a science that employs the methods and principles of physics and chemistry in the study of astronomical objects and phenomena. As one of the founders of the discipline, James Keeler, said, Astrophysics "seeks to ascertain the nature of the heavenly bodies, rather than their positions or motions in space–what they are, rather than where they are." 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.
Vera Florence Cooper Rubin was an American astronomer who pioneered work on galaxy rotation rates. She uncovered the discrepancy between the predicted and observed angular motion of galaxies by studying galactic rotation curves. By identifying the galaxy rotation problem, her work provided evidence for the existence of dark matter. These results were later confirmed over subsequent decades.
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.
Eleanor Margaret Burbidge, FRS (née Peachey; 12 August 1919 – 5 April 2020) was a British-American observational astronomer and astrophysicist. In the 1950s, she was one of the founders of stellar nucleosynthesis and was first author of the influential B2FH paper. During the 1960s and 1970s she worked on galaxy rotation curves and quasars, discovering the most distant astronomical object then known. In the 1980s and 1990s she helped develop and utilise the Faint Object Spectrograph on the Hubble Space Telescope. Burbidge was also well known for her work opposing discrimination against women in astronomy.
Willem de Sitter was a Dutch mathematician, physicist, and astronomer.
Donald Lynden-Bell CBE FRS was a British theoretical astrophysicist. He was the first to determine that galaxies contain supermassive black holes at their centres, and that such black holes power quasars. Lynden-Bell was President of the Royal Astronomical Society (1985–1987) and received numerous awards for his work, including the inaugural Kavli Prize for Astrophysics. He worked at the University of Cambridge for his entire career, where he was the first director of its Institute of Astronomy.
The Herschel Medal is awarded by the Royal Astronomical Society (RAS) for "investigations of outstanding merit in observational astrophysics". It is awarded for a single piece of work so that younger scientists can be candidates for the award. It is named after the RAS's first president, William Herschel. The medal was first awarded in 1974. From 1974 to 2004 the Herschel Medal was only awarded every three years. From 2004 the frequency was shortened to two years and from 2012 it will be awarded annually. The medal has been shared twice, in 1977 and 1986. It has been awarded 23 times to a total of 25 people, mostly from the UK.
Gravitational-wave astronomy is a subfield of astronomy concerned with the detection and study of gravitational waves emitted by astrophysical sources.
Catherine Heymans is a British astrophysicist, the Astronomer Royal for Scotland, and a professor at the University of Edinburgh based at the Royal Observatory, Edinburgh.
Georges Meylan is a Swiss astronomer, born on July 31, 1950, in Lausanne, Switzerland. He was the director of the Laboratory of Astrophysics of the Swiss Federal Institute of Technology (EPFL) in Lausanne, Switzerland, and now a professor emeritus of astrophysics and cosmology at EPFL. He is still active in both research and teaching.
Giovanni Fazio is an American physicist at Center for Astrophysics | Harvard & Smithsonian. He is an astrophysicist who has initiated and participated in multiple observation programs.
Stephen Eales is a professor of astrophysics at Cardiff University, where he is currently head of the Astronomy Group. In 2015, he was awarded the Herschel Medal from the Royal Astronomical Society for outstanding contributions to observational astrophysics. He also writes articles and books about astronomy.
