Parallax: Quick Facts

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Photos

Diagram illustrating how astronomers calculate the distance to a star using parallax: Earth is shown in two positions on opposite sides of its orbit around the Sun, with lines extending to a nearby star X and further to distant background stars. The apparent shift in star X's position, measured as angle A, is used to determine its distance, with the baseline labeled as 186,000,000 miles.

Change of parallactic angle with altitude.

Measurement of parallax by observations from a northern and a southern observatory.

Diagram illustrating stellar parallax, showing Earth at two points in its orbit around the Sun, with lines connecting each position to a distant star and forming an angle labeled p to represent the parallax shift.

Diagram showing binocular and instantaneous parallax, with two eyes labeled NL and NR, and lines from each eye converging on two points, A and B, to illustrate depth perception.

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Topics

stellar parallax solar parallax lunar parallax secular parallax moving cluster parallax spectroscopic parallax trigonometric parallax convergent point Charlier’s method Astronomical observatory reference frame How Do We Know How Far Away the Stars Are?position vector astrolabe Heliometer Proper motion Gravitational microlensing Zone of avoidance

Key People

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Frank Schlesinger

American astronomer

Gill, Sir David

Sir David Gill

Scottish astronomer

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Jean Richer

French astronomer

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Thomas Henderson

Scottish astronomer

Nicolaus Copernicus. Nicolas Copernicus (1473-1543) Polish astronomer. In 1543 he published, forward proof of a Heliocentric (sun centered) universe. Coloured stipple engraving published London 1802. De revolutionibus orbium coelestium libri vi.

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