Properties of Galaxies

Dive into 26.3 Properties of Galaxies to explore how the masses of spiral and elliptical galaxies are determined, their mass-to-light ratios, and the presence of dark matter within galaxies.
To measure the distance to galaxies, astronomers look for “standard candles” within these galaxies. A standard candle is any object that shines with a known luminosity. If astronomers know how much light the object gives off and they know how faint it appears in our night sky, then they can easily calculate how far away the galaxy is. Watch the teacher video Standard Candles for a review of the two most useful standard candles for measuring distances to galaxies: supernovae and Cepheid variables.
Read 26.4 The Extragalactic Distance Scale to learn more about how astronomers measure distances to galaxies using various methods, including cepheid variables, type Ia supernovae, and the Tully-Fisher relation.
Galaxies are far more enormous than anything we have studied so far in this class. You might be surprised, though, to learn about how far apart they are spread. Watch the teacher video Galactic Distances for an introduction to the scale of distances between galaxies.