PHYS 1000 Lecture Notes - Lecture 14: Milky Way, Cosmic Distance Ladder, Spiral Galaxy

• School: University of Windsor
• Department: Physics
• Course: PHYS 1000
• Professor: Mr.Mark Lubrick

Document Summary

Although difficult to estimate, there is likely hundreds of billions of galaxies (maybe more). From earth, we see few stars when looking out of galaxy, many when looking in. One of the first attempts to measure the milky way was done by herschel using visible stars. Unfortunately, he was not aware that most of the galaxy, particularly the centre, is blocked from view by vast clouds of gas and dust. We have already encountered variable stars nova and binary system. There are other stars whose luminosity varies in a regular way, but this is an intrinsic trait of the star itself. Two types of pulsating variable stars that have been very important: rr lyrae stars and cepheids. The upper plot is an rr lyrae star. All such stars have essentially the same luminosity curve, with periods from 0. 5 to 1 day. The lower plot is a cepheid variable; cepheid periods range from about 1 to 100 days.