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

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Orion Glossary


Browse the glossary using this index

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H

habitable zone

The range of distances from a star within which an Earth-like planet would be habitable.


Harvard Spectral Classification

A commonly used classification scheme for stars by which the temperature of a star is denoted by the assignment of a letter in the sequence OBAFGKM, running from hottest (O) to coolest (M)


helium burning

The process by which stars fuse three helium nuclei into one carbon nucleus via the triple alpha process.


Hertzsprung-Russell (HR) diagram

A diagnostic diagram whereby the evolutionary state of a star may be discerned via a combination of stellar temperature and luminosity. Named after its originators Ejnar Hertzsprung and Henry Norris Russell.


hot Jupiter

A giant planet, with a mass close to or greater than that of Jupiter, and which orbits very close to its parent star.


Hubble deep field

A project with the Hubble Space Telescope to obtain a series of very deep exposures to search for distant galaxies at high redshift.


Hubble’s law

The observation that, for distant galaxies, the greater a galaxy’s distance, the greater the redshift of the radiation received from that galaxy.


hydrogen burning

The process by which stars on the main sequence release energy via the conversion of hydrogen into helium in their cores.


hydrogen shell burning

The process by which, in post-Main Sequence stars, hydrogen is converted into helium in a thin shell exterior to the core.


hydrostatic equilibrium

In a star, the state at which physical forces directed inwards are exactly balanced by those directed outwards.



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