parallax
n.n. the difference in the position of an object when you look at it from two different places. In astronomy, it helps scientists measure how far away a star is from Earth.
n. the apparent displacement or difference in position of an object viewed from two different points not on the same line of sight. In astronomy, it refers to the angular difference in the apparent position of a celestial body as seen from two different points in Earth's orbit.
Astronomers use parallax to measure the distance to nearby stars.
By observing the same star from opposite sides of the Earth's orbit, scientists calculated its parallax to determine its exact distance.
The measurement of stellar parallax provides a fundamental baseline for the cosmic distance ladder, allowing astronomers to calibrate the distances to more distant galaxies.
From Middle French parallaxe, from Ancient Greek παράλλαξις (parállaxis, “alteration”) from παραλλάσσω (parallássō, “to cause to alternate”) from ἀλλάσσω (allássō, “to alter”) from ἄλλος (állos, “other”). By surface analysis, par- + all- + -ax.