sciencesoup:

Spectroscopy: Astronomy’s most powerful tool

For a long time, much of the universe was a mystery because it seemed so far out of reach, but the emergence of spectroscopy in the 19^th century has allowed us to study the distant skies using the only information we have: light. Amazingly, it’s shown us that everything in the known universe is made up of the same elements we find here on Earth. Basically, spectroscopy uses the light of a star, planet or galaxy to decipher its properties. The light is separated out according to wavelength much like a prism separates out colours, and a spectrum is then generated: a unique pattern of lines that can show us all of the elements present in the star, almost like a cosmic barcode. Because an atom of a certain element will both emit and absorb the same frequency of electromagnetic radiation, we can detect what elements make up a star in two different ways, depending on our vantage point. Firstly, using the emission spectrum, which is produced by elements that emit radiation of a specific wavelength when heated, and secondly using the absorption spectrum, which is produced by elements absorbing certain wavelengths of light travelling outwards through the star, then re-radiating it in another direction, giving us dark lines in our spectrum. However, if we were looking at the star from the direction of the re-radiation, we would then view the spectrum as emission and not absorption. It all depends on perspective.

(Image Credit: 1, 2)