| half-moon |
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noun
- the moon, in its first or last quarter, when only half the face is illuminated
- anything shaped like a crescent, especially the base of a fingernail
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| Halley's Comet |
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proper noun
- A very bright comet which can be seen every 75-76 years.
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| HALO |
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abbreviation - (parachuting) High Altitude, Low Opening.
- When you have enough experience, you can do a HALO jump.
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| heliacal |
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adjective - Of or relating to the sun, especially rising and setting with the sun.
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| heliocentric |
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adjective - (astronomy) having the sun at the center/centre; usually in reference to a solar system or orbit
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| heliograph |
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noun
- An apparatus for signalling by means of a moveable mirror which reflects flashes of sunlight.
- A heliogram.
- An instrument for measuring the intensity of sunlight.
- A device for photographing the sun.
- (obsolete) A photograph.
verb
- (transitive) To send a message by heliograph.
- (intransitive) To send a heliograph.
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| heliopause |
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noun - (astronomy) The boundary of heliosphere where the Sun's solar wind is stopped by the interstellar medium.
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| Hercules |
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proper noun
- (greekmyth) Son of Jupiter and Alcmene, a celebrated hero who possessed exceptional strength. Most famous for his 12 labors performed to redeem himself after killing his family.
- (constellation) A summer constellation of the northern sky, said to resemble the mythical hero. It lies between the constellations Lyra and Corona Borealis.
- (astronomy) A crater in the first quadrant on the moon.
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| Hermes |
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proper noun
- (Greek mythology) the herald and messenger of the gods, and the god of roads, commerce, invention, cunning, and theft.
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| Hertzsprung-Russell diagram |
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noun - (star): a plot of the absolute magnitude of stars versus their colour (or surface temperature); shows the main sequence of stars plus the white dwarfs and red giants
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| horizon |
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noun
- The horizontal line that appears to separate the Earth from the sky.
- The range or limit of one's knowledge, experience or interest.
- (geology) A specific layer of soil or strata
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| horn |
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noun (horns, -)
- (countable) A hard growth of keratin that protrudes from the top of the head of certain animals.
- (uncountable) The hard substance from which animals' horns are made, sometimes used by man as a material for making various objects.
- an umbrella with a handle made of
- (countable) Any of several musical wind instruments.
- (countable) An instrument resembling a musical horn and used to signal others.
- hunting
- (countable) A loud alarm, especially one on a motor vehicle.
- (countable) A conical device used to direct waves.
- antenna
- loudspeaker
- (context, informal, countable) Generally, any brass wind instrument.
- (context, slang, countable, from the horn-shaped earpieces of old communication systems that used air tubes) A telephone.
- (context, uncountable, coarse, slang, definite article) An erection of the penis.
- (context, countable, coarse, slang, definite article) A peninsula or crescent-shaped tract of land. "to navigate around the horn."
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| Hubble's constant |
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noun (context, singulare tantum)category:English nouns
- alternative spelling of Hubble constant
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| Hubble's law |
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noun (context, singulare tantum)category:English nouns
- alternative spelling of Hubble law
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| Hunter's Moon |
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noun the
- The full moon after the Harvest Moon.
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| Hyades |
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proper noun
- (astronomy) An open cluster of stars in the constellation Taurus, and the nearest visible such cluster to Earth.
- (greekmyth) Daughters of the Titan Atlas and sisters of the Pleiades.
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| Hydrus |
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proper noun
- (constellation) A winter constellation of the southern sky, said to resemble a small serpent. It lies between the constellations Mensa and Tucana. It is not to be confused with the constellation Hydra.
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| Hyperion |
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proper noun
- (Greek mythology) A Titan, the son of Gaia and Uranus and the father of Helios, Selene and Eos.
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