Before You Begin
There are four fundamental tasks to this lab:
Along the way, you will:
- Find a pre-assigned number of Cepheid variables in the galaxy
- Use the periods and average apparent magnitude of the Cepheids,
and the Period-Luminosity relation, to determine the distance to M100.
- Estimate the Hubble constant, which represents the current rate of
expansion of the universe.
- 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
- 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
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 "10x" 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
- 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 10x.
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.
On to Measuring Cosmic Distances
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