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H

Habitable Zone:

A planet on the close to edge of the habitable zone will have a surface temperature slightly lower than the hot point of water. A planet on the distant edge of the habitable zone will have a surface temperature somewhat higher than the freezing point of water.

Heliocentric:

An adjective sense “centered on the Sun.”

Host Galaxy:

A galaxy in which a space phenomenon, such as a supernova or even explosion and a gamma-ray burst that has occurred.

Hubble Constant (Ho):

A number that express the rate at which the space expands with time. Ho appears to be among 60 and 75 kilometers per second per mega parsec.