Determining distances to galaxies

Aims:

In this project, you are going to use the relationship that Henrietta Leavitt discovered to find out

how far away four Cepheid variable stars are from us. There are three steps in the process:

1. Find the apparent luminosity and period of the Cepheids from their light curves (the period

is the time between two peaks in the Cepheid's brightness).

2. Find the actual luminosity of the Cepheids from their periods.

3. Find the distance of the Cepheids from the apparent and actual luminosities.

1. Finding the apparent luminosity:

The graphs below show the light curves for four variable Cepheids over several weeks. Note how

regular the variation is for each. The vertical axis gives the apparent luminosity of the Cepheids.

? Start by using the horizontal scale on these graphs to find the period of each of these stars.

? Then use the vertical scale on the graphs to find the average apparent luminosity

? Enter this information in the data table on page 4.

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