- heliumThe second-lightest chemical element (symbol He), with an atomic number of 2 and atomic weight of 4.002602, a colorless, odorless and inert noble gas.
- heliosThe god of the Sun; son of Hyperion and Theia, brother of Selene and Eos, father of Phaeton amongst others. His Roman counterpart is Sol.
- helianthophobiaThe fear of sunflowers (plant).
- helio-Concerning the sun.
- heliodorA richly coloured form of golden beryl found in southwest Africa.
- helioliteA variety of feldspar, closely related to orthoclase
- heliometerAn astronomical instrument, based on a telescope, for measuring the diameter of the sun; now used to measure the angular distance between stars and other celestial bodies.
- heliostatA device that includes a plane mirror which turns so as to keep reflecting sunlight toward a predetermined target, compensating for the sun's apparent motions in the sky. The target may be a physical object, distant from the heliostat, or a direction in space, and is almost always stationary relative to the heliostat, so the light is reflected in a fixed direction.
- heliotypyA method of transferring pictures from photographic negatives to hardened gelatin plates from which impressions are produced on paper as by lithography.
- isohelA line on a map connecting places that receive equal solar radiation, or equal daily hours of sunshine.