Supernovae Lab

Supernovae Activity - Online

Purpose: To derive a relationship between supernovae distances and their redshifts.

Directions:

For each supernova follow the link to its light curve, and find and click on the maximum brightness (m) on the curve. Remember the lower the number, the brighter the supernova is.
Find and record the distance modulus for each supernova, the distance modulus is defined: D=m-M, where m=the observed maximum brightness and M is the absolute brightness for supernovae: -19.12.
Use the Distance modulus (D) to find and record the actual distance in parsecs: d(distance in pc)=10^(D+5)/5 and in km 1pc=3.09x10¹³km.
Return to this page using the link at the bottom of each light curve page.
Proceed to the red shift measurement section at the bottom of the page.
For each of the ten links measure the redshift as described in the next step.
When you click on the link you will see a graph of the spectrum of the supernova. The name of the supernova will appear at the top of the graph. This graph shows the amount of light (flux) for each color (wavelength of light) which reaches the spectrometer from the supernova. Specifically, this spectrum is an absorption spectrum. The general hill shape of the graph shows the temperature of the supernova, and the bumps and wiggles show which elements have absorbed the light as it travelled from the supernova to the detector that took the spectrum. As you may remember the spectrum of the supernova is like its "finger print". For these supernovae, we will be measuring the Silicon II line. This is the dip in the graph that a doubly ionized atom of silicon would make when it absorbs the light from the supernova. If the supernova were not moving with respect to Earth, the Silicon II line would appear at 6150 Angstroms (6150 x 10^-10m), much as a car horn that is still remains at the same pitch. However, the Si II line is redshifted, indicating that the supernova is moving away from Earth similiar to the change in pitch that you experience as a car horn moves away from you which is known as the Doppler Shift. The red line on the graph indicates where 6150 Angstroms falls on the graph and the Si II "line" appears as the closest dip or trough to the right of the red line. Notice that because the Si II line moves to the right of the graph, its wavelength is longer. The light has been stretched out, which causes it to move towards the redder end of the electromagnetic spectrum which is why it is called, Red Shift.
1. Click on the graph as close as you can to the center bottom of the trough. The screen will flash and return with the flux and wavelength that you have measured listed at the top of the screen.
2. If you wish to remeasure simply click again on the graph.
3. Record the wavelength.
4. Calculate the redshift: (Your measured wavelength - 6150)/6150.
5. Return to this page by following the link at the top of each spectrum page or follow the link to the next spectrum.
Make a plot of the Distance in Megaparsecs (1Mpc=10⁶ parsecs) versus the Speed (Speed=redshift * the speed of light, 3.0 x 10⁵ km/s).
Draw a line on the graph which you think comes nearest to the most of your data points as possible.
Try to find a relationship between the speed and the distance. (How does one relate to the other, could you suggest a mathematical equation? Remember this is real data so there may be some error and the equation may not be exact.)