Orion Glossary
habitable zoneThe range of distances from a star within which an Earth-like planet would be habitable. |
Harvard Spectral ClassificationA 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 burningThe process by which stars fuse three helium nuclei into one carbon nucleus via the triple alpha process. |
Hertzsprung-Russell (HR) diagramA 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 JupiterA giant planet, with a mass close to or greater than that of Jupiter, and which orbits very close to its parent star. |
Hubble deep fieldA project with the Hubble Space Telescope to obtain a series of very deep exposures to search for distant galaxies at high redshift. |
Hubble’s lawThe observation that, for distant galaxies, the greater a galaxy’s distance, the greater the redshift of the radiation received from that galaxy. |
hydrogen burningThe process by which stars on the main sequence release energy via the conversion of hydrogen into helium in their cores. |
hydrogen shell burningThe process by which, in post-Main Sequence stars, hydrogen is converted into helium in a thin shell exterior to the core. |
hydrostatic equilibriumIn a star, the state at which physical forces directed inwards are exactly balanced by those directed outwards. |