Eli5: how do we know the properties of things in space like stars and planets if we’ve never been on them?

Question

Eli5: how do we know the properties of things in space like stars and planets if we’ve never been on them?

In: Other

Answer 1

We measure them from a safe distance. We’ve only been on the Moon. Everyplace else in the Universe is only known through distant observation or near observation by robotic space probes.

That said, you don’t measure the temperature of lava in a volcano by going to the lava either. From a safe distance you make your measurements because lava is not human-friendly.