Before You Begin

1. Find a pre-assigned number of Cepheid variables in the galaxy M100.
2. Use the periods and average apparent magnitude of the Cepheids, and the Period-Luminosity relation, to determine the distance to M100.
3. Estimate the Hubble constant, which represents the current rate of expansion of the universe.
4. Use your derived value of the Hubble constant to estimate the age of the universe.

• Learn the basics of the cosmological distance scale, and how astronomers tackle a problem which cannot be addressed directly.
• Learn something about digital astronomical images, specifically those taken by the Hubble Space Telescope's Wide Field and Planetary Camera 2.
• Learn how the blink technique allows one to easily discern variable phenomena on complicated images.

Plan on 2 to 3 hours to do the lab. 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.

Hardware and software requirements:

• This lab is specifically designed for Netscape 2.0 and higher.
• You will need a computer screen with reasonable resolution and graphics capabilities. You may need to adjust the contrast and brightness as you do the lab.
• Some browsers or machines may not display superscripts and subscripts properly. If "10^x" does not look like 10 raised to the power of x, and "log₁₀" does not look like the word "log" with a subscript of 10, there is a hardware or software problem. If you cannot remedy the problem, you may have to use another computer. Most of the equations in this lab have superscripts and/or subscripts.
• You will need to print a copy of the lab sheet. Even if your screen properly displays superscripts and subscripts, check to see that your printout properly displays them. Otherwise, parts of your lab sheet could be incorrect.

• You will need your lab sheet, a pen or pencil, and a calculator that has the functions log₁₀ and 10^x.

Many links to external Web pages have been provided for those who are interested. These optional pages are intended to introduce some of the many fine astronomy Web pages.

The lab is intended to be fun. You should 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.

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