An Etymological Dictionary of Astronomy and Astrophysics
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A zone around a star within which a planet can have temperatures that permit liquid water, depending on the luminosity of the star and the distance of the planet from it.

→ circumstellar; → habitable zone.

A region of the Galaxy whose boundaries are set by its calm and safe environment and access to the chemical materials necessary for building terrestrial planets similar to the Earth. → circumstellar habitable zone; → habitable zone.

→ galactic, → habitable; → zone.

A zone around a → star where the → temperature would be in the range 0-100 °C to sustain → liquid water on the surface of rocky planets (or sufficiently large moons). Water is thought to be a necessary component to the → formation and evolution of Earth-type life. This zone depends on the parent star's luminosity and distance; it will be farther from hotter stars. A more accurate definition of HZ needs to include other factors, such as orbital → eccentricity, heat sources other than stellar irradiation, and atmospheric properties. Same as → circumstellar habitable zone; → ecosphere.

→ habitable; → zone.