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In the night sky: Orion
In the night sky: Orion

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Orion Glossary


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S

speed of light

The speed at which light travels. It is equal to approximately 300 million metres per second (3 × 108 m s−1). Often denoted by the letter c as in Einstein's famous equation, E = mc2.


star

A luminous gaseous body that is gravitationally bound and that is capable, or was capable in the past, of sustaining itself against gravitational collapse by thermonuclear reactions. Until the very late stages of their evolution, stars are composed mostly of hydrogen and helium, which are the most abundant elements in the Universe.


star clusters

Star clusters are physically compact groupings of tens to millions of stars which formed simultaneously in the same region of space.


supergiant

A star, several times more massive than the Sun, after it has exhausted its hydrogen nuclear fuel supply.


supermassive black hole

A term used to describe black holes, implying that they have very much more mass than would be expected from a black hole that originated as the remnant of a single star.


supernova

A dramatic stellar explosion, produced when a star several times the mass of the Sun has exhausted its nuclear fuel.


T

terrestrial planet

A planet similar in size to the Earth, composed of rocky materials (cf. giant planet).


thermal pulses

Thermal pulses are brief bursts of enhanced energy production in solar mass stars due to the instabilities inherent in helium shell burning.


triple-alpha process

A sequence of nuclear fusion reactions that occurs in the cores of high-mass stars. In this sequence, three helium nuclei are converted into a carbon nucleus.


W

wave

A periodic (regularly repeating) disturbance that transports energy from one place to another, characterised by its wavelength, frequency (or period) and amplitude.



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