spectral lines

[blackeyed]

Can anyone explain to me what are spectral lines?
I'd be really grateful.

[jake-the-peg]

If an electron in an orbit (shell) of an atom moves from a higher more energetic shell to a lesser energetic shell it emits a photon of light. that light has a particular frequency given by f=E/h where E is the energy and h is something called Plancks constant.

This means that if you split up light with a prism or diffraction grating in a device called a spectrometer you can see bright lines. These bright lines correspond to these changes in electron energy levels and are called emission spectral lines.

Because every material has its own unique set of possible electron orbitals the result is a kind of fingerprint of the material that made the light.

In fact the element Helium was first discoverred by it's spectral fingerprint in light from the sun Long before it was isolated on Earth.

If you pass white light through a material electrons will absorb the same specific frequencies and you get dark spectral lines we see these in light from stars like the sun as the light is absorbed it gasses in their upper atmosphere.

We can also tell from a bodies spectral lines how fast it may be moving away from us.

Sodium has a very distinctive pair of yellow lines in it's spectrum. If you measure the light from a galaxy and find those lines not in the yeallow but down in the Red you know that that body must be moving away from you very fast and you are seeing it as red because the galaxy is moving away from you so quickly that the light is spread out to a longer wavelength.

Sometimes these are called Fraunhoffer lines after the Physicist who first worked on them

http://en.wikipedia.org/wiki/Fraunhofer_lines

You can learn a lot of other things by studying spectral lines - there are entire modules in University courses on them. Th

[blackeyed]

thanx a lot JTP for your very good answer but can you also explain what is a spectrometer?