The Northwestern University Astronomy Web Lab Series

adapted for use at Western Kentucky University

Measuring the Distance to a Nearby Galaxy


How far away are the stars we can see in the night sky?

How far away are the galaxies beyond our Milky Way?

In this lab you will focus on a particular technique that is useful for measuring distances to neighboring galaxies, and the nearest galaxy clusters. You will use actual Hubble Space Telescope (HST) images to find the distance to a galaxy named M100, by measuring the brightness variations of particular stars known as Cepheid variables.

Along the way, you will learn some basics about digital astronomical images, about detecting variable phenomena, and how astronomers tackle a problem which cannot be addressed directly.

Feel free to do the lab at whatever pace you wish. If you find yourself getting bored with background material in the first sections, move on to the next section. You can always go back to previous pages to learn any background you missed.

Note: The lab sheet does not have all the information you need to do the lab. Please be sure to read the associated Web pages as you work through the lab sheet.


Begin Lab Activity Resume Lab: resume previous work
Tutorial pages:

References and Bibliography


Last updated: 7 April 2006
Richard Gelderman (