Stars, black holes and galaxies

Our universe is defined by stars. This topic explores how they came to be and where they end up. This includes a discussion of black holes and galaxies.

Quasars and galactive collisions

Quasars are the brightest objects in the universe. The gamma rays from them could sterilize a solar system (i.e. obliterate life). What do we think these objects are? Why don't we see any close by (which we should be thankful for)? Could they tell us what our own galaxy may have been like 1 billion or so years ago?
Quasar correction
Quasar Correction
Galactic collisions
Collision of the Milky Way Galaxy with Andromeda (forming "Milkomeda")

Stellar parallax

We've talked a lot about distances to stars, but how do we know? Stellar parallax--which looks at how much a star shifts in the sky when Earth is at various points in its orbit--is the oldest technique we have for measuring how far stars are. It is great for "nearby" stars even with precise instruments (i.e, in our part of our galaxy). To measure distance further, we have to start thinking about Cepheid variables (other tutorial).
Parallax in observing stars
Parallax in Observing Stars
Stellar parallax
Another version of the stellar parallax introduction
Stellar distance using parallax
Stellar Distance Using Parallax
Stellar parallax clarification
Stellar Parallax Clarification
Parsec definition
Parsec Definition

Cepheid variables

Stellar parallax can be used for "nearby" stars, but what if we want to measure further out? Well this tutorial will expose you to a class of stars that helps us do this. Cepheids are large, bright, variable stars that are visible in other galaxies. We know how bright they should be and can gauge how far they are by how bright they look to us.
Cepheid variables 1
Cepheid Variables 1
Why cepheids pulsate
Why Cepheids Pulsate
Why gravity gets so strong near dense objects
Why Gravity Gets So Strong Near Dense Objects