Stellar parallax and the distance ladder – basic principles
How it works
Stellar parallax is the apparent shift of a star against the background of very distant objects when the Earth moves on its orbit. It is an important proof of the Earth's motion and is used to measure the distances to nearby stars. The parallax angle is determined from observations that are typically about six months apart. The distance in parsecs is obtained as the reciprocal of the parallax angle in arcseconds: d = 1/p. For greater distances, other methods of the distance ladder are used, for example Cepheids, Type Ia supernovae or, on very large scales, redshift. Each method is suitable only for certain objects and distance ranges and builds on the calibration of earlier stages.
The distance of a nearby star in parsecs is calculated as the reciprocal of its measured parallax angle in arcseconds: d = 1/p. For greater distances, other methods of the distance ladder are used, which are based on known luminosities or spectroscopic properties.
An example
A star has a measured parallax of 0.2 arcseconds. How far away is it?
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50 Exercises
To the learning unit →Own explanation and own practice exercises by AmyMath. Subject reference framework: Astronomy. The topic assignment may vary by federal state.