[ELI5] How can scientists know about the makeup of distant celestial bodies?

Question

I can understand the mass stuff since you can see how they attract/orbit etc, but how can they say stuff like “This planet has a thin atmosphere of 80% sulphur monoxide and 18% helium and it rains nano-diamonds periodically”.

How can you get all this stuff from looking through a telescope?

In: Physics

Answer 1

The scientific name for it is [Astronomical Spectroscopy](https://en.wikipedia.org/wiki/Astronomical_spectroscopy). As the others have explained, atoms can absorb or emit light, and depending on their electron configuration, the frequencies of light (colors) that are absorbed or emitted will have certain bands that a sensitive spectrometer instrument can detect. It’s possible to identify each element, hydrogen, helium, oxygen, etc., because they each have different electron configurations, and thus different [spectra](https://en.wikipedia.org/wiki/Emission_spectrum).