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Glossary of Astronomy Terms
beginning with letter H
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half-moon Tweet Definition of half-moon Like Definition of half-moon on Facebook
noun
  1. the moon, in its first or last quarter, when only half the face is illuminated
  2. anything shaped like a crescent, especially the base of a fingernail
Halley's Comet Tweet Definition of Halley Like Definition of Halley
proper noun
  1. A very bright comet which can be seen every 75-76 years.
HALO Tweet Definition of HALO Like Definition of HALO on Facebook
abbreviation
  1. (parachuting) High Altitude, Low Opening.
    When you have enough experience, you can do a HALO jump.
heliacal Tweet Definition of heliacal Like Definition of heliacal on Facebook
adjective
  1. Of or relating to the sun, especially rising and setting with the sun.
heliocentric Tweet Definition of heliocentric Like Definition of heliocentric on Facebook
adjective
  1. (astronomy) having the sun at the center/centre; usually in reference to a solar system or orbit
heliograph Tweet Definition of heliograph Like Definition of heliograph on Facebook
noun
  1. An apparatus for signalling by means of a moveable mirror which reflects flashes of sunlight.
  2. A heliogram.
  3. An instrument for measuring the intensity of sunlight.
  4. A device for photographing the sun.
  5. (obsolete) A photograph.
verb
  1. (transitive) To send a message by heliograph.
  2. (intransitive) To send a heliograph.
heliopause Tweet Definition of heliopause Like Definition of heliopause on Facebook
noun
  1. (astronomy) The boundary of heliosphere where the Sun's solar wind is stopped by the interstellar medium.
Hercules Tweet Definition of Hercules Like Definition of Hercules on Facebook
proper noun
  1. (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.
  2. (constellation) A summer constellation of the northern sky, said to resemble the mythical hero. It lies between the constellations Lyra and Corona Borealis.
  3. (astronomy) A crater in the first quadrant on the moon.
Hermes Tweet Definition of Hermes Like Definition of Hermes on Facebook
proper noun
  1. (Greek mythology) the herald and messenger of the gods, and the god of roads, commerce, invention, cunning, and theft.
Hertzsprung-Russell diagram Tweet Definition of Hertzsprung-Russell diagram Like Definition of Hertzsprung-Russell diagram on Facebook
noun
  1. (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
horizon Tweet Definition of horizon Like Definition of horizon on Facebook
noun
  1. The horizontal line that appears to separate the Earth from the sky.
  2. The range or limit of one's knowledge, experience or interest.
  3. (geology) A specific layer of soil or strata
horn Tweet Definition of horn Like Definition of horn on Facebook
noun (horns, -)
  1. (countable) A hard growth of keratin that protrudes from the top of the head of certain animals.
  2. (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
  1. (countable) Any of several musical wind instruments.
  2. (countable) An instrument resembling a musical horn and used to signal others.
hunting
  1. (countable) A loud alarm, especially one on a motor vehicle.
  2. (countable) A conical device used to direct waves.
antenna
loudspeaker
  1. (context, informal, countable) Generally, any brass wind instrument.
  2. (context, slang, countable, from the horn-shaped earpieces of old communication systems that used air tubes) A telephone.
  3. (context, uncountable, coarse, slang, definite article) An erection of the penis.
  4. (context, countable, coarse, slang, definite article) A peninsula or crescent-shaped tract of land. "to navigate around the horn."
Hubble's constant Tweet Definition of Hubble Like Definition of Hubble
noun (context, singulare tantum)category:English nouns
  1. alternative spelling of Hubble constant
Hubble's law Tweet Definition of Hubble Like Definition of Hubble
noun (context, singulare tantum)category:English nouns
  1. alternative spelling of Hubble law
Hunter's Moon Tweet Definition of Hunter Like Definition of Hunter
nounthe
  1. The full moon after the Harvest Moon.
Hyades Tweet Definition of Hyades Like Definition of Hyades on Facebook
proper noun
  1. (astronomy) An open cluster of stars in the constellation Taurus, and the nearest visible such cluster to Earth.
  2. (greekmyth) Daughters of the Titan Atlas and sisters of the Pleiades.
Hydrus Tweet Definition of Hydrus Like Definition of Hydrus on Facebook
proper noun
  1. (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.
Hyperion Tweet Definition of Hyperion Like Definition of Hyperion on Facebook
proper noun
  1. (Greek mythology) A Titan, the son of Gaia and Uranus and the father of Helios, Selene and Eos.

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