The Earth and Beyond
The Universe - Big Bang - Red-Shift - Line Spectra.
When we say
that light from other galaxies is red-shifted
we mean that light in line spectra appears at longer wavelengths.
familiar with the idea that different
show different colours in a flame test.
Sodium is yellow/orange, potassium is lilac, lithium is red.
particular colour which an
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.
spectrum below shows three important lines for sodium.
If the above sodium spectrum is
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
changing colour as they go. This is called the red-shift.
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Copyright © 2012 Dr. Colin France. All Rights Reserved.