AST201H1 Lecture Notes - Lecture 15: Inverse-Square Law, White Dwarf, Cosmic Distance Ladder

• School: UTSG
• Department: Astronomy & Astrophysics
• Course: AST201H1
• Professor: Michael Reid

Document Summary

Ast201: hubble"s law and the expanding universe (chp 20. 2-20. 3) In the early 1920s, edwin hubble measured the distances to spiral nebulae and proved that they were well outside the milky way. Standard candles like cepheids (pulsating variable stars: measuring a cepheid"s period allows us to determine its luminosity and calculate its distance (with the inverse square law for light, the longer the period, the more luminous the star. Obeys a period luminosity relation: we can determine its luminosity by measuring the period btw its peaks in brightness and then use this luminosity to determine the distance. Hubble also noticed that the spectra of most distant galaxies were redshifted. Hubble found that, the more distant a galaxy was, the larger its redshift (for distant galaxies only. It"s btw 21-23 km/sec/ million light yrs (galaxy"s speed away from us is btw 21 and 23 km/s for every million light yrs of distance from us)