(Greek mythology) The god of the Sun; son of Hyperion and Theia, brother of Selene and Eos, father of Phaeton amongst others. His Roman counterpart is Sol.

(historical) A sunroom or solarium of the Ancient Greeks.

plural of helio

Concerning the sun.

A heliotrope (surveying instrument).

Sunstroke. / Sunburn. / Exposure to the sun. / Scorching of plants by the sun.

(astronomy) An apparatus for viewing the Sun without harming the eye, by means of an optical filter that attenuates most of sunlight while allowing only a small amount of the solar radiation.

A 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.

(astronomy) The region of space where interstellar medium is blown away by solar wind; the boundary, heliopause, is often considered the edge of the Solar System.

plural of helioscope