Galaxies

The solar system is just a tiny speck within a galaxy of hundreds of billions of stars — itself one among hundreds of billions of others.

Types of galaxies

Spirals, ellipticals, irregulars: the major families of galaxies and what sets them apart.

Galactic structure

Bulge, disk, halo, and the supermassive black hole hiding at the center of the Milky Way.

Large-scale phenomena

Galaxy clusters, dark matter, dark energy, and the ongoing expansion of the universe.

Black holes

Event horizon, stellar and supermassive black holes, and the first image ever captured.

Big Bang

How the universe began, cosmic inflation, and the cosmic microwave background.

Dark matter and dark energy

What we can't see but can measure: 95% of the universe's contents.