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Lecture 8

PHYS 1600 Lecture 8: F11_PHYS-1600 - Week 8

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PHYS 1600
Elizabeth Nicol

PHYS 1600 Week 8 Unit 8 Study Guide 11- 1 – Distances to nearby stars are determined by stellar parallax. The closest star other than the sun, proxima Centuari, in the constellation centuarus, is about 40 trillion km away. Light takes more than 4 years to get from here to there. The apparent motion of nearby stars among the background of more distant stars, due to earth’s motion around the sun is called stellar parallax. The word parsec (from parallax second) originated from the use of parallax to measure distance. Distance to a star in parsecs = __________________1___________ Parallax angle of that star in arc seconds Or d=1 P Where d is the distance to the star and p is the parallax angle of that star. Distance to a star in light years = 3.26 Parallax angle of that star in arc seconds Example: the nearest star, proxima centauri has a parallax angle of 0.77 arcsec, and so its distance is 1/0.77 or approximately 1.3 pc. Equivalently proxima centuari is 4.24 light years (ly) away. The parallax of proxima centauri is comparable to the angular diameter of a dime seen from a distance of 3km. the parallax angles of the 25 nearest stars are listed in appendix table E-5. As earth moves from one side of its orbit around the sun to the other a nearby stars apparent position 11-1c, the parallax angle, p, is half the angle by which earth shifts positions through the year as seen from that star, measured in arcseconds. The first stellar parallax measurement was made in 1838 by Friedrich Wilhelm Bessel, a German astronomer and mathematician. Downloaded free at PHYS 1600 Week 8 Earth based telescopes gives stellar distance only up to 100 pc. Telescopes in are unhampered by our atmosphere and therefore have higher resolutions than earth based telescopes. Parallax measurements made in space thus enable astronomers to determine the distance to stars well beyond the reach of ground based observations. Combining the distances and the varied brightness we observe will enable us to calculate how much light stars actually emit, and thereby to explore their evolution. The magnitude scales were created before accurate measurements of the relative brightness of stars could be made, and they have since been refined. The original first magnitude stars were about 100 times brighter than the original sixth magnitude stars. Therefore astronomers chose the brightness factor of exactly 100 to define the range of stars. IN other words, it takes 100 stars of apparent magnitude m = +6 to provide as much light as we receive from a single star of apparent magnitude m= +1. Going from m = +6 to m = +5 increases (multiplies) the brightness we see by the same factor as going from m = +5 to m = +4 and so on. Going from m = +6 to m = +1 requires multiplying the same brightness facto
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