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apsides

Overview page. Subjects: Astronomy and Astrophysics — Physics.

The two points in an astronomical orbit that lie closest to (periapsis) and farthest from ( apoapsis) the centre of gravitational attraction. The line of apsides is the straight line that...

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axion

Overview page. Subjects: Astronomy and Astrophysics — Physics.

A hypothetical elementary particle postulated to explain why there is no observed CP violation (see CP invariance) in the strong interaction (see fundamental interactions). Axions have not...

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baryon

Overview page. Subjects: Astronomy and Astrophysics — Physics.

Any member of a class of subatomic particles that includes protons and neutrons, as well as numerous others such as the Σ+ (sigma-plus) and Ω (omega-minus) particles. Together with the...

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big Bang

Overview page. Subjects: Physics — Astronomy and Astrophysics.

The hypothetical but widely accepted ‘explosive’ event that marked the origin of the universe as we know it. At the time of the Big Bang, the entire universe was squeezed into an infinitely...

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binding energy

Overview page. Subjects: Physics — Astronomy and Astrophysics.

The energy released when protons and neutrons bind together to form an atomic nucleus, or the energy required to break up that nucleus. The binding energy per proton or neutron is greatest...

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Brans–Dicke theory

Overview page. Subjects: Physics — Astronomy and Astrophysics.

An alternative to Einstein's theory of general relativity which attempts to incorporate Mach's principle. Among other things, this theory predicts that the value of Newton's gravitational...

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carbon cycle

Overview page. Subjects: Physics — Astronomy and Astrophysics.

A series of nuclear reactions in which four hydrogen nuclei combine to form a helium nucleus with the liberation of energy, two positrons, and two neutrinos. The process is believed to be...

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Chandrasekhar limit

Overview page. Subjects: Physics — Astronomy and Astrophysics.

The maximum possible mass of a degenerate star, above which it will be unable to support itself against the inward pull of its own gravity. For a star with no hydrogen content the limit is...

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coelostat

Overview page. Subjects: Astronomy and Astrophysics — Physics.

A device that enables light from the same area of the sky to be continuously reflected into the field of view of an astronomical telescope or other instrument. It consists of a plane mirror...

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communications satellite

Overview page. Subjects: Astronomy and Astrophysics — Physics.

An unmanned artificial satellite sent by rocket into a geostationary orbit (see synchronous orbit) around the earth to enable television broadcasts and telephone communications to be made...

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