AST 301 Lecture Notes - Lecture 39: Spiral Galaxy, Weakly Interacting Massive Particles, Star Formation
Document Summary
Dying stars expel gas and new elements, producing hot bubbles. Hot gas cools, allowing atomic hydrogen clouds to form. Further cooling permits molecules to form, making molecular clouds. Gravity forms new stars and planets in molecular clouds. The interstellar medium that makes new star systems. Making stars dimmer and redder is called interstellar extinction. William and caroline herschel (1785) were astronomers trying to map the shape based on observations using the law of physics. They assumed there is no extinction/ nothing obscuring our view, and stars have the same brightness. New way of getting distance- cepheid variables in the lmc. The lo(cid:374)ger a cepheid"s period, the greater its lu(cid:373)i(cid:374)osit(cid:455) is. After calibrating using cepheids with known distance, we can measure the period and m to find how far away the star is. The more luminous the cepheid, the longer its pulsation period. Rr lyrae variables are horizontal-branch stars that all have roughly the same avg. luminosity of about 100 l.
