Simplified Activity 2 The Signature of the Stars

The Expanding Universe
Activity 2
The Signature of the Stars
1. Every element produces a unique line spectrum of light which can be used to identify the elements
present in a distant galaxy. If the galaxy is moving away from us, the lines will be shifted toward the
red end of the spectrum. This shift is like the Doppler shift of sound when an ambulance moves away
from us. In that situation the original sound becomes
A) higher, louder
B) lower, louder
C) higher, quieter
D) lower, quieter
2. Astronomers noticed that the spectra of galaxies were shifted toward the red end of the spectrum
(longer wavelengths) .This means they are moving away from us. The table below shows two of the
lines for Calcium. Use the speed scale at the bottom to determine the speeds of each galaxy.
3. Which graph would you expect If you plotted the distance on the vertical axis vs. speed?
Explain your choice.
Activity 2
The Expanding Universe
1. Plot the distance to the galaxy on the y-axis and the speed of each galaxy on the x-axis.
2. Draw a line of best fit. Should it include (0, 0)? Explain.
3. The points are scattered around the line instead of being right on it. What might cause this?
4. Calculate the slope of the line using two points on the line. Circle the two points that you
used. Show your calculations below. Don’t forget to include units and powers of ten.
5. Change the unit of the slope into years. Show your steps below.
6. What is the meaning of this time?
Activity 2