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The distance to a star if it has a parallax angle of one arcsecond (1/3600 of a degree). The parallax angle is half the angular distance that a nearby star appears to move by, relative to distant background stars, when the Earth travels half way around its orbit. One parsec is equal to 3.26 light-years.

Parallax. The apparent motion of a near by star is a small ellipse in the sky relative to background stars over the period of a year.

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