heliometer
/ˌhiliˈɑmɪtər/
noun
- A scientific instrument originally designed to measure the diameter of the sun, later used for measuring small angles in astronomy.
- The museum displayed a 19th-century heliometer used in solar research.
- Early heliometers were difficult to operate but provided precise data.
- The astronomer used a heliometer to measure the sun's apparent diameter.