Question

Wein’s law applies to blackbody spectra, and blackbody spectra are perfectly smooth curves. However these spectra all have a bunch of dips in them. What are these dips, how are they created, and what do they tell us about the stars?

Answer 1

Blackbody spectra are perfectly smooth curves, that is blackbody emits radiation at all the possible wavelengths. However before this radiation reaches us sometimes it passes through gas clouds which are cooler than the stars.

Hence some wavelengths will be strongly absorbed by these gas clouds. When we analyze the radiation, on the other side of the gas cloud the spectra will have bunches of dips in them. These dips correspond to absorbed wavelengths. Such a spectrum is called an absorption spectrum. By analyzing the missing wavelengths the constituents of gas clouds can be predicted. This tells us about the outer layers of stars.

Helium was first found on sun using such abosorption spectra.