Solar projection instrument. Historical artwork of apparatus being used to project an image of the sun onto a plate marked with mathematical indicators. Instead of risking the health of their eyesight, astronomers would analyse the sun's surface patterns and sunspots by observing the projection produced by this type of equipment. This engraving is from the book Rosa Ursina sive Sol, written by Christoph Scheiner (1573-1650) in 1630.