1848, "instrument for taking photographs of the sun," from helio- "sun" + -graph "something written." Earlier, "a description of the sun" (1706, implied in heliographic). From 1877 as the name of a movable mirror used in signaling. Related: Heliographical.
Heliography (1845) was the word for the product of a type of engraving process by chemical reaction from exposure to sunlight. It also was an early term for what came to be called photography (1840).
