# PHYS 1000 Lecture 10: Chapter 10 Notes

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12 Feb 2018
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## Document Summary

There is likely several tens of sextillions (1021) of stars in the universe. Parallax: look at the apparent motion of an object against a distant background from 2 vantage points; knowing from baseline allows calculation of distance. *distance (in parsecs) = 1/parallax (in arc seconds)* Where 1 parsec is 206, 265 au or 3. 1 x 1016 m or 3. 3 light years. Nearest star to the sun: proxima centauri, which is a member of a 3-star system: alpha centauri complex. The 30 closest stars to the sun *diagram*. A star has 2 velocity components: radical velocity velocity towards us along the line of sight (doppler effect) transverse velocity velocity perpendicular to our line of sight (parallax corrected) Ba(cid:396)(cid:374)a(cid:396)d"s sta(cid:396) has the la(cid:396)gest proper motion the actual shift of the star in the sky (after correcting for parallax). Luminosity, or absolute brightness, is a measure of the total power radiated by a star.