A historical optical instrument for projecting an image of the sun onto a screen using special lenses and mirrors.
From Greek helios (sun) + opticon (from optikos meaning 'related to sight'). Named following 19th-century conventions for optical instruments like the microscope and telescope.
The heliopticon was like the solar system's first projector—astronomers could safely study sunspots and solar features without looking directly at the sun, which would cause instant, permanent blindness!
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