gcsescience.com                                       43                                       gcsescience.com

Stars and the Universe

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.

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 that 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.
Line Spectrum

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.
Line Spectra showing Red-Shift

The lines have moved towards the red end of the spectrum
changing colour as they go. This is called the red-shift.

back    Links    Universe    The Solar System    Revision Questions    next

gcsescience.com      Physics Quiz      Index      The Universe Quiz      gcsescience.com

Home      GCSE Chemistry      GCSE Physics

Copyright © 2015 gcsescience.com. All Rights Reserved.