On this night in science
Galileo sees Neptune without knowing it
December 28, 1612
On this night in 1612, Galileo was watching Jupiter through his telescope when he sketched a faint star nearby. It wasn't a star at all: it was the planet Neptune, which no one would recognize as a planet for more than two hundred years.
Why it mattered
Neptune moves so slowly across the sky that it looked like any other star. Even great scientists can see something amazing and not know it yet.
Wonder together
How could you tell whether a tiny point of light is a star or a planet?