So, I've begun my World of Cinema class. In class on Wednesday, earlier in the week, we watched a film called Back to God's Country, directed by Nell Shipman, a Canadian writer/director/actress from the early 20th century. Back to God's Country is a silent film, made in 1919. What a fascinating film about a virtuoso female filmmaker!

Quasars are the most luminous examples of an active galactic nucleus. They are found very far away from us, and some quasars are millions of times brighter than our Sun but occupy a very small region of space. Quasars are powered by the energy created as gravitational potential energy turns into kinetic energy as matter falls into a black hole.

Method 1: Main Sequence Fitting (finding distances by comparing main sequence stars of different clusters).

1. Identify a nearby cluster with known distance (from parallax), and thus get the luminosities of its main sequence stars - standard candle.
2. Take a faraway cluster's main sequence stars and compare their brightness to the std. candle.
Since stars of the same color have the same luminosity, the difference in their apparent brightness would be proportional to the distance between them.

Method 2: Cepheid Variables

Cepheid stars are very luminous and vary in brightness with periods ranging from days to months. Cepheid variable stars with longer periods have greater luminosities (Period-Luminosity Relation).
Because the period of a Cepheid variable star tells us its luminosity, we can use these stars as standard candles. Gives distances up to 100 million ly.

Method 3: White Dwarf Supernovae As Standard Candle

White-dwarf supernovae can also be used as standard candles, because they happen in similar stars and hence should have similar luminosities.
Apparent brightness of white-dwarf supernova tells us the distance to its galaxy (up to 10 billion light-years)

Method 4: Tully-Fisher Relation:

Entire galaxies can also be used as standard candles galaxy luminosity is related to rotation speed: as both are related to mass in the galaxy (higher the mass, the more luminosity, as well as rotational speed).