Using a Hertzsprung Russell diagram and cephid variables to estimate distance in astronomy

Supporting notes are at http://www.fizzics.org/Pages/Measuring-astronomical-distances.aspx The video sets out to explain real and apparent magnitude and how we use the observed magnitude and colour of a star to measure the distance from earth using a Hertzsprung Russell diagram. In the second part an explanation of the use of stars of variable brightness as standard candles to estimate the distances of remote galaxies containing a Cepheid variable.