Question: How is Spectroscopy used to analyse interstellar nebulaas

Andrew McKinley answered on 20 Nov 2014:

If you look at a nebula through a telescope you will see all the colours of that nebula. You will also have (hopefully) seen using a prism to split white light into its component parts (see the icon of the Spectroscopy Zone in the top left of this page!). If you are able to split the sunlight up enough, with a wide enough dispersion (this will take more than just a prism!), you start to see dark lines. This link to the National Optical Astronomy Observatory shows you the expanded solar spectrum (it is over multiple lines – you ‘read’ this like a book – start at the first line, go left to right, then next line, left to right). The ‘dark lines’ we are interested in appear as ‘gaps in the spectrum:

Each of these ‘gaps’ is due to the absorption of a particular element, and this gives us a ‘fingerprint’ of the elements in our sun. This is the exact opposite of the flame tests – if we burn a metal, it gives out a particular colour, but if we have enough of it in a plasma (like the sun), it will actually absorb that same colour and we see it as a gap in the spectrum.

We can use the exact same technique on distant nebulae to identify what elements are present – we look for the dark lines, and we know the wavelength that each one absorbs, so we can see what elements make up the interstellar ‘nursery’.