helio-, heli-

(Greek: sun)

Heliopolis
An ancient city of northern Egypt in the Nile River delta north of modern Cairo. It was the center of worship of the sun god Ra until the rise of Thebes (c. 2100 B.C.).

Its importance as the historical repository with famed schools of philosophy and astronomy declined after the founding of Alexandria in the fourth century B.C.

Two of its obelisks, both known as "Cleopatra's Needle", are now in London and in New York City's Central Park.

Helios
The god of the sun.
heliosciophyte (s) (noun), heliosciophytes (pl)
A plant which thrives in both sunlight and shade, but which grows best in sunny conditions.
helioscope
A telescope with a great focal length that receives images of the sun from plane mirrors attached to it; so, the viewer's eyes are protected from the sun's glare.
helioseismology
1. The study of sun quakes by observing the structure, composition, and dynamics of the sun from indirect observations of acoustic waves on the sun's surface.
2. The study of the sun's internal structure using observations of the frequencies and strengths of normal mode oscillations detected at the surface by their Doppler shifts.

Such vibrations were first discovered in the 1960s by researchers at the California Institute of Technology.

heliosheath
The region of the heliosphere beyond the termination shock where the wind is slowed, compressed, and made turbulent by its interaction with the interstellar medium.
heliosis
Sunstroke or thermic fever; a condition produced by exposure to the sun, and marked by convulsions, coma, and a high temperature of the skin.
heliosphere
1. The region of space where solar and planetary particles and magnetic fields are dominant.
2. A spherical region around the sun, approximately 100 astronomical units in radius, outside which interstellar space begins.
3. The region of space through which the solar wind extends and the region around the sun outside of which the sun's influence is negligible and interstellar space begins.
heliostat (s) (noun), heliostats (pl)
An instrument which uses a mirror that automatically adjusts to the sun's position and and directs the sunlight in a continuous beam or direction: A heliostat, which was clock-driven, was put outside a window on the 8th floor of the office building in order to provide solar radiation in the large room.
heliotaxis, heliotactic
1. The movement of an organism in response to sun light.
2. Movement of an organism toward (positive) or away from (negative) sunlight.
3. Movement, as of a plant, in response to sunlight; heliotropism.
heliotherapy (s) (noun), heliotherapies (pl)
1. The use of the sun's rays for therapeutic treatment purposes: Heliotherapy has long been used as a treatment for various skin conditions.
2. The treatment of certain diseases by exposing the body to sunlight: Heliotherapy is also known as "solar therapy" or "solar treatment".
heliotherm
1. An organism that warms its body in the direct rays of the sun.
2. A reference to organisms that maintain a comparatively high body temperature by basking in sunlight.
heliothermal
Any process which uses solar radiation to produce useful heat.
heliothermia
heliothermic
1. Construction planning that provides for natural solar heating and cooling processes and their relationship to a building's shape, orientation, and siting.
2. A description of a lake whose temperature increases, rather than decreases, with depth.
3. Descriptive of a creature absorbing heat and energy from the sun.

This term is sometimes used in place of ectothermic, or "cold-blooded".

Related "sun" word family: sol-.