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

Start this free course now. Just create an account and sign in. Enrol and complete the course for a free statement of participation or digital badge if available.

Orion Glossary

Browse the glossary using this index

Special | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | ALL

Page: (Previous)   1  ...  3  4  5  6  7  8  9  10  11  12  (Next)


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.


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.


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.


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


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.



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

Page: (Previous)   1  ...  3  4  5  6  7  8  9  10  11  12  (Next)

Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has 50 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to University-level study, we offer two introductory routes to our qualifications. You could either choose to start with an Access module, or a module which allows you to count your previous learning towards an Open University qualification. Read our guide on Where to take your learning next for more information.

Not ready for formal University study? Then browse over 1000 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus371