hubble-space-telescope

Astronomers' galaxy counts have swung from 100 billion to 2 trillion and back to hundreds of billions. Here's why the number keeps changing, and what it actually means.

A telescope gathers more light than the eye and resolves finer detail. Galileo's 1609 refractor showed him moons around Jupiter. ESO's 39.3-meter Extremely Large Telescope collects nearly a million times more light than Galileo's lens, once adaptive optics cancels the blur of Earth's atmosphere.