SLOW

Have you ever wondered how astronomers can just look at a star, or any other distant object, and know exactly what combination of elements it's made of? The trick of how this is done was partly explained to me in John Gribbin's Deep Simplicity, and completely elucidated by Simon Singh in the equally excellent Big Bang.

The answer lies with spectroscopy: All you do is take the light wave you captured, spread it so you can see the whole spectrum from infrared to ultraviolet, and look for the missing bits. Every element has a unique bunch of lines that are missing that identify it precisely. For example, one element might miss a bit of red and a bit of green, whereas another might miss a bit of red and a bit of violet.

These missing lines are known as Fraunhofer lines or absorbtion lines. They provide clues about a multitude of the properties of the object being observed. The reason these lines are missing is because the elements absorb or decrease the intensity of a particular part of the spectrum.

Follow this link for a good visual illustration of spectroscopy.

Anyone looking for interesting meta-scientific reading will be well advised to seek out the books of Gribbin and Singh. And next time you look at the sun, know that some hydrogen and helium have already been filtered out and if you look really (really!) carefully, you might be able to notice it.

# posted by Slow @ 9:08 am