Unit 27
Galaxies and cosmology.
The largest scale: galaxies and their arms, the dark matter in their spin, and the oldest light there is.
Before this unit
The unit, lesson by lesson
Lessons
3 lessons · 18 practice questions · about an hour
Galaxies
Islands of billions of stars: why a spiral galaxy’s arms are blue and why they don’t wind up, what an elliptical galaxy’s colour tells, and how long the Sun takes to go round the Milky Way.
Dark matter and rotation curves
Weighing a galaxy by its stars’ speeds: the speeds do not fall at the edge, so it holds far more mass than shines, spread in a halo round it.
The cosmic microwave background
The oldest light we can see: a glowing fog that filled the young universe, cleared about 380,000 years after the Big Bang, and has stretched into microwaves since.