Earth & SkyGreek → English
Parallax
/ˈpærəlæks/noun
The apparent shift of an object against its background when the observer moves.
The Greek roots
παρά
pará
beside, alongside
ἀλλάσσω
allássō
to change, alter
Literally: “a change alongside”
The story of the word
Greek παράλλαξις meant an alternation or a shifting about, nothing astronomical. Sixteenth-century astronomers took it for the shift they had to correct out of their measurements, and it became the great test of Copernicus: if the earth moved, the nearer stars should visibly shift. None did, to the instruments of the day, and the argument stalled until Bessel measured the parallax of 61 Cygni in 1838.
- How it travelled
- Ancient Greek → Modern Latin → French → English
- First recorded
- 1590s
Same family
parallacticparasiteallegoryparody
In a sentence
Read the gauge straight on, or parallax will cost you a few millilitres.