Earth & SkyGreek → English
Heliometer
/ˌhiːliˈɒmɪtər/noun
A telescope with a split object glass, used to measure very small angles in the sky.
The Greek roots
ἥλιος
hḗlios
sun
μέτρον
métron
measure
Literally: “sun measurer”
The story of the word
Cut the objective lens in half, slide the halves apart, and the distance needed to bring two images into coincidence gives you an angle with great precision. It was built for the sun's diameter, hence the name. Bessel then pointed the Königsberg heliometer at 61 Cygni and in 1838 published the first trustworthy distance to a star, a little over ten light years, settling a question open since Copernicus.
- How it travelled
- Ancient Greek → scientific coinage → English
- First recorded
- 18th century
Same family
heliumheliotropeperihelionheliograph
In a sentence
The heliometer sat on its pier for forty years and outlived two directors.
Parallax work with a heliometer demanded thousands of separate readings.