eli5: Prior to actual imagery from space, how did scientists know what distant objects looked like?

Question

Was it I’m a math equation? Was it a wild guess?

In: 6

Answer 1

There are very few things out there that we couldn’t see pretty well from Earth. Probes and space telescopes can give us tremendous detail, but we could already see all the planets, nebulae and galaxies using Earth-based telescopes.