parallax
UK[ˈpærəlæks]US[ˈpærəˌlæks]
n
the apparent displacement or difference in the apparent position of an object viewed along two different lines of sight.
n
the angular amount of such a displacement or difference, used in astronomy to measure distances.
Morpheme Breakdown
para
allax
para
beside, beyond
allax
change
Etymology
the word parallax entered english in the late 16th century, directly from the greek 'parallaxis', meaning "alteration". this greek term itself is a compound of 'para-' (beside) and 'allassein' (to change). the core logic is that of a change in position when seen from two different vantage points. in its scientific application, this literal sense of "change beside" perfectly captures the phenomenon where an object appears to shift against a distant background when the observer's position changes, a principle fundamental to astronomical measurement.
Analysis
Structure: para (beside, beyond) + allax (change)
para is a prefix of greek origin meaning "beside, beyond, altered". allax is from the greek verb 'allassein', meaning "to change".
Examples
astronomers use stellar parallax to calculate the distance to nearby stars.
the parallax error occurs when the reading on a dial is taken from an angle rather than directly head-on.
high-end rifle scopes are designed to eliminate parallax for greater accuracy.