Stellar parallax

The difference in direction of a star viewed from the two ends of a line with a length equal to the radius of the Earth’s orbit is called the PARALLAX of the star.

Stars that are close to the earth clearly have a larger parallax than ones far away. In other words their direction when viewed from the Earth changes significantly as the Earth orbits the Sun. By significantly we mean a fraction of a second of arc. For example alpha Centauri (distance 1.33 parsecs) has a parallax of 0.75" of arc.

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