Astronomy 1-24
22 entries in the Astronomy compendium.
Cosmic inflationTheory of exponential early universe expansion explaining cosmic structure.Cosmic rayHigh-energy particles from space, discovered via balloon flights in 1912.Cosmological constantA coefficient in Einstein's equations explaining cosmic acceleration.Crab NebulaSupernova remnant and pulsar wind nebula in Taurus.Dark nebulaDense interstellar clouds that block visible light from background objects.Dwarf galaxySmall galaxies shaped by larger neighbors and dark matter.Eris (dwarf planet)Dwarf planet whose discovery redefined the Solar System's planetary lineup.Event horizonA spacetime boundary beyond which no signal can reach an observer.ExoplanetAn exoplanet, or extrasolar planet, is a planet located outside the Solar System. The discExtinction (astronomy)Extinction dims and reddens starlight via interstellar dust and gas.Extraterrestrial lifeHypothetical life originating from worlds beyond Earth.Galaxy formation and evolutionStudy of galaxy origins, structure, and change over cosmic time.Galaxy groups and clustersLargest gravitationally bound objects in cosmic structure formation.Galaxy morphological classificationA system for classifying galaxies by visual appearance and structure.Giant planetA massive planet composed mainly of volatiles, not solid matter.Giant starGiant stars are luminous, expanded post-main-sequence stars.H II regionIonized hydrogen regions where new stars are born.Halley's CometFirst comet recognized as periodic, observed for over two millennia.Hertzsprung–Russell diagramScatter plot linking stellar luminosity and temperature.Hubble's lawGalaxies recede faster the farther they are from Earth.Hyades (star cluster)Nearest open cluster, key rung on the cosmic distance ladder.Elliptical galaxyElliptical galaxies are smooth, ellipsoidal galaxies with old stars.
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