In this lecture I explain:

What Cepheid variable stars are
The shape of their luminosity time graph and how to find their period using the graph
How the shape of Cepheid variables varies with time, and how the shape affects the luminosity
How Cepheid variable stars are used to measure distance
How to find the luminosity of a Cepheid variable star given its period and vice versa
How to find the distance to a Cepheid variable star given its period and brightness as observed from Earth
Why Cepheid variables are important in the history of astronomy
Henrietta Leavitt's discovery of the relationship between the period of a Cepheid star and its luminosity
Why Cepheid variable stars are in a category of stellar objects called "Standard Candles"

0:00 Definition
0:23 Luminosity vs Time Graphs
1:35 Astronomy before Cepheids
3:31 Henrietta Leavitt
3:52 A problem with measuring distance in space
5:23 Leavitt's idea
6:34 The Magellanic Clouds
7:30 Luminosity vs. Period graphs
10:50 Finding distance to Cepheids
12:45 Example Problem
14:14 Standard Candles

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