To make students more familiar with the measurement of red shift and the relation Hubble found, try the activity at the following Web site:

http://www.astro.washington.edu/labs/hubble. This activity is very well explained and shows students how to measure galactic red shift with provided images and tools.

With the data they have collected from the web, have the students calculate their redshifts and velocities using the equations listed above. Then have the students make a plot of velocity versus distance. They may have to make use of their experience with scaling from previous exercises to fit the graphs on normal graph paper.

What your students should discover is that their plots form a straight line. Have your students calculate the slope of this line, and a possible equation to determine the velocity as a function of distance. Hubble found this equation to be:

Velocity = "constant" x distance.

This "constant" is now called the Hubble constant. As mentioned before the value of this "constant" is still being debated, for as your students may discover, the points fall very close but not exactly on a straight line, more data are needed before we are really sure. Therefore, the equation for velocity could actually be a slightly steeper line, or possibly not even a line at all. Today, typical values of the Hubble constant range from 50 to 100 km s^-1 Mpc^-1.

 

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