Parallax measurement of distance. Diagram showing the principle of measuring astronomical distances using parallax. Parallax is the shift of a nearby object against a distant background when viewed from two different positions. Here,a nearby star is viewed from either side of Earth's orbit (lower centre),the largest possible baseline. Parallax measurements are given in parsecs,where an object with a 6-month parallax shift of 2 seconds of arc is at a distance of one parsec. 1,296,000 seconds of arc circle the sky. One astronomical unit (AU,the Earth-Sun distance) is 150 million kilometres. A parsec is 30,900 trillion kilometres. Parallax can be detected for stars up to 100 parsecs away | |
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Crédit: | Science Photo Library / Lomberg, Jon |
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