INTRODUCTION
In this lab, you will be creating and analyzing the visible spectra recorded both in a laboratory and from five distant galaxies. Using this data, you will determine if these galaxies are in motion towards or away from the Earth and the relative speed at which they are moving. You can download the handout here.
STEP #1
Color in each of the six blank spectra on your lab sheet to show the colors of the visible spectrum. Use the data table below to see where each color should go on the spectra.
VIOLET
390-455 nm
BLUE
455-492 nm
GREEN
492-577 nm
YELLOW
577-597 nm
ORANGE
597-622 nm
RED
622-700 nm
STEP #2
Energy with a wavelength less than 390 nm is called ultraviolet. Please label (but don't color) this on each of your spectra. Energy with a wavelength longer than 780 nm is called infrared. Please also label (but don't color) this on each of your spectra. Keep in mind, some of the galaxies may have spectra that are shifted entirely off the portion that we are looking at. Don't worry about drawing any lines that are off the spectra provided on your handout.
STEP #3
Use the data table on the right to determine the location of each spectral line for the standard spectra and for several distant galaxies. Mark with a dark, black vertical line, the location of each of the spectral lines in each spectrum. Extend your lines slightly above and below each spectrum.
| SPECTRUM | LOCATION OF SPECTRAL LINES (nm) |
|---|---|
| Standard Spectrum | 420, 450, 530, 640, 656 |
| Virgo A Galaxy | 440, 470, 550, 660, 676 |
| Coma Pinwheel Galaxy | 470, 500, 580, 690, 706 |
| Andromeda Galaxy | 380, 410, 490, 600, 616 |
| Cetus A Galaxy | 430, 460, 540, 650, 666 |
| M65 Spiral Galaxy in Leo | 620, 650, 730, 840, 856 |
STEP #4
Let's figure out why the spectra of these galaxies look different. An object’s motion affects the energy emitted by that object. If it is moving away, the wavelength of the light it is emitting is stretched. If it is moving towards you, the wavelength of the light it is emitting is compressed. See the image to the left. Please watch this video on the doppler shift before proceeding. When you are done, use this information to answer the conclusion questions on the back of your lab sheet.