PCS 181 Lecture : unit 2 galaxies.docx

• School: Ryerson University
• Department: Physics
• Course: PCS 181
• Professor: Margaret Buckby

Document Summary

The identification of other galaxies, or independent stellar systems, goes back to 1924, when edwin hubble found cepheid variables in the nearby galaxies messier 33 and. Application of the period-luminosity relation for these variables in the. Magellanic clouds established that these were objects outside the confines of the milky. More thorough studies show that galaxies exhibit a wide range of properties, from giant galaxies of 1013 solar masses and sizes over. 150,000 pc in diameter to dwarf galaxies of 106 solar masses and about 1,000 pc in size. Dwarf galaxies are by far the most numerous. It is estimated that about 100 billion galaxies in the universe are observable with existing telescopes. Hubble quickly realized that the vast majority of galaxies have only a small number of shapes. A classification based on their optical appearance or morphology is limited to four fundamental types of galaxies ellipticals, spirals, irregulars, and s0s.