What is "helioscope"

Helioscope \He"li*o*scope\, n. [Helio- + -scope: cf. F. h['e]lioscope.] (Astron.) A telescope or instrument for viewing the sun without injury to the eyes, as through colored glasses, or with mirrors which reflect but a small portion of light. -- He`li*o*scop`ic, a.

n. (context astronomy English) An apparatus for viewing the sun without injuring the eye.

A helioscope is an instrument used in observing the sun and sun spots. The helioscope was first used by Benedetto Castelli (1578-1643) and refined by Galileo (1564–1642). The method involves projecting an image of the sun onto a white sheet of paper suspended in a darkened room with the use of a telescope.

The first machina helioscopica or helioscope was designed by Christoph Scheiner (1575 –1650) to assist his sunspot observations.