AST 301 Lecture Notes - Lecture 41: Globular Cluster, Light-Year, Photon
Document Summary
What do we want to know about the universe. Cosmology is everything we want to know about the universe. If the u(cid:374)i(cid:448)erse is i(cid:374)fi(cid:374)ite i(cid:374) size, age, a(cid:374)d is isotropi(cid:272) the(cid:374) it does(cid:374)"t (cid:373)atter (cid:449)here (cid:455)ou look, (cid:455)ou"d see a star a(cid:374)d the sk(cid:455) (cid:449)ould radiate as bright as the sun. Therefore: the universe has finite size, finite age, universe is expanding. The distance to a galaxy determines how big of a shift toward the red we see its spectrum. All galaxies move away from each other. The further a galaxy is from another galaxy, the greater the difference. Within a galaxy cluster, where gravity is stronger than the expansion of space, you can have motion towards each other. But outside the cluster the galaxies recede from you. The redshift is not due to the doppler effect, but it is cosmological, the metric of the universe changes. A light wave traveling through an expanding universe stretches, and wavelength increases.
