Knowra Stellar parallax Stellar parallax Stellar parallax is the apparent positional shift of a nearby star against distant background stars as Earth orbits the Sun. Its angle provides a geometric measure of the star’s distance.
Parallax angle : The angular displacement of an object’s apparent position caused by a change in viewpoint. Half the star’s annual apparent shift is the angle used in the distance calculation.
Friedrich Bessel : A German astronomer who made the first successful stellar parallax measurement, for 61 Cygni, in 1838. His measurement established that stellar distances could be found geometrically.
Gaia (spacecraft) : A European Space Agency space observatory that measures positions, parallaxes, and motions of stars. Its repeated all-sky observations have measured parallaxes for more than a billion stars.
Stellar distance : The physical separation between a star and an observer, commonly measured in parsecs or light-years. Parallax provides a direct geometric estimate of this quantity for nearby stars.
Astronomical unit : The mean distance between Earth and the Sun, defined as exactly 149,597,870,700 metres. Earth’s orbital baseline is one astronomical unit from the Sun to either side.
61 Cygni : A binary star system in the constellation Cygnus, notable for its large proper motion and early parallax measurement. Bessel measured its parallax to demonstrate the method in 1838.
Hipparcos : A European Space Agency astrometry satellite that operated from 1989 to 1993 and produced a precise stellar catalogue. It established space-based parallax measurements before Gaia’s much larger survey.
Absolute magnitude : The apparent magnitude a celestial object would have at a distance of 10 parsecs. A parallax distance allows a star’s intrinsic brightness to be expressed as absolute magnitude.
Parsec : A distance unit equal to the distance at which one astronomical unit subtends one arcsecond. A star one parsec away has a parallax angle of one arcsecond.
Thomas Henderson : A Scottish astronomer who measured the parallax of Alpha Centauri in the 1830s. His observations yielded a nearby star’s distance, though publication followed Bessel’s result.
Show all 23