1. Variable Stars

2. Changing Light
Some stars have been known to change their luminosity over time.
The AAVSO (American Association of Variable Star Observers) provides history, tips and current news.

3. Properties of Variables
Light curves are used to track the luminosity of a variable star with time.
Measure period and amplitude
Some stars are very regular, while others are irregular.

4. Extrinsic Variables Eclipsing Binaries
Binary stars vary in apparent luminosity as one member eclipses another.
Contact Binaries
If binary stars come into contact from gravity.

5. Recurring Novae
Gas from one star in a binary can be transferred to the primary star.
Luminosity flares up and down
Irregular pattern
As this pattern repeats, the star is a variable star.

6. Intrinsic Variables As giants, stars can become unstable.
The temperature and luminosity fluctuate as the gas expands and contracts.
These are pulsating variables.
unstable region

7. Standard Candle
The best measure of large distances are variable stars.
Pressure and radiation precisely oscillate
Luminosity directly related to the period
The apparent magnitude and period give the distance.
Pressure increases as helium heats up
Pressure decreases as helium ionizes and cools
Process repeats

8. RR-Lyrae RR-Lyrae stars are low mass pulsating variables. About 1 M
Period less than a day
Used for cluster distances

9. Cepheids
Large mass stars that pass through the unstable region are known as Cepheid variables.
From 5 M to 20 M
Period of 1 to 100 days
Cepheids are important to measure distances to other galaxies.