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The Universe - Big Bang - Red-Shift - Line Spectra.
Links in Pink will take you to the GCSE Chemistry site.
When we say
that light from other galaxies is red-shifted
we mean that light in line spectra appears at longer wavelengths.
We are
familiar with the idea that different
elements
show different colours in a flame test.
Sodium is yellow/orange,
potassium is lilac, lithium is
red.
The
particular colour which an
element shows
depends on the difference in
energy between its electron shells.
Light is emitted at a particular wavelength
(colour) when
electrons move
from a high energy (outer)
shell to a lower
energy (inner) shell.
The colour which we see is a combination
of a number of different wavelengths
as electrons move between different shells in
the same atom.
We can see these different
wavelengths as lines on a spectrum
for a particular element.
The
spectrum below shows three important lines for sodium.
If the above sodium spectrum is
compared
with spectra for sodium from other
galaxies,
you can see that the positions of the
lines have changed.
The lines have moved
towards the red end of the
spectrum
changing colour as they go.
This is the red-shift.
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Copyright © 2008 Dr. Colin France. All Rights Reserved.