Distance to a Star
Distance Units:
-A light year (ly) is the distance that light can travel in one year, which is 9.5 trillion km, so 1 ly = 9.5
trillion km.
-One parsec (pc) is equal to 3.26 light years.
-An arcsecond is the measure of the angle of apparent change in a star’s position.
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Measuring Distance:
-Stellar Parallax: The measurement of the shift of a nearby star because of the earth’s revolution around
the sun.
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It only works for stars up to 1,000 light years away.
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Stars further away have less change.
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Parallax Examples:
-The star Sirius has a parallax of 0.37921 arcseconds. (1/1000 of a degree) What is the distance in light
years?
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Parallax is 0.37921 arcseconds
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Distance is 1/parallax
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Distance = 1/0.37921 arcseconds
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Distance is 2.367 parsecs
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To convert parsecs into light years, multiply 2.367 by 3.26(ly in a parallax).
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The distance is 8.6 ly
-A star has a parallax of 0.76887 arcseconds. What is the star’s distance from earth in light years?
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Parallax is 0.76887 arcseconds
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Distance is 1/p
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Distance is 1/0.76887 arcseconds
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Distance is 1.3 parsecs
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To convert into light years, multiply 1.300 by 3.26.
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The distance is 4.2 ly
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