# Variable Stars

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• Created by: KingOlir
• Created on: 29-04-17 14:50

## Binary Stars

One of the reasons we have variable stars is due to some of them being Binary Stars. These are stars which have smaller star orbiting around them.

These stars fluctuate at regular intervals. At certain points, the star will seem dimmer.

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## Cepheid Variables 1

Another reason for variable stars are stars called Cepheid Variables. Their magnitudes go through regular, periodic fluctuations.

The reason for this is that, while most stars have an equilibrium between their gravitational pull inwards and their forces from nuclear fusion outwards and thus they maintain a fairly constant brightness, Cepheid Variables do not keep this stable state. Periodically, the star pulsates as the gravitational pull overpowers the outward forces keeping the star together, but then resets as the outward force catches up with the gravitational force.

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## Cepheid Variables 2

We can use the time period (the amount of time it takes for the variable star to undergo a full cycle) of a Cepheid Variable star to find out its absolute magnitude using a graph similar to the one on here, and using that absolute magnitude, we can find the star's distance from Earth using a rearrangement of the equation:

M = m + 5 - 5*log*d

Using this graph, we can work out the absolute magnitude of a Cepheid Variable, which means that we can work out the distance to that star. This is vital for working out distances to far away systems, for which using parallax does not work.

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