University of Michigan - Department of Astronomy

Version: Luminosity

Spectral Classification and the Pleiades - Worksheets

Table 1: The Pleiades Spectral and Magnitude Data

Star Number Spectral Type Spectral Lines Used To Classify Photo Diameter Flux (W/m2) Apparent magnitude


Average Value: L/ f = ________________________.

Distance equation:


d = _________________

Turn in you graph and table with the worksheets. 

Concluding Questions

  1. If you plot flux vs. spectral type for a random group of stars in the sky, why don't you trace out main sequence? Why do you see a main sequence when you plot the data for the stars in the Pleiades?

  2. What quantities did you plot for the standard stars? What quantities can we actually directly observe for these stars? What do we need to know about these stars to obtain the quantities you plotted?

  3. What conditions would be necessary to use spectroscopic parallax to find the distance
    to a galaxy?

Part 4 (optional)

Fill in the values of m for the pleiades stars in the table at the begining.

Attach your magnitude-spectral type H-R diagram and table of m and M values to the worksheet.

Distance Modulus: _____________________

distance calcuation:

d = _____________________

Part 4 Questions

  1. How did you know what unit d was in when you plugged in the distance modulus?

  2. Would a bigger distance modulus mean a cluster is closer, or farther away? Explain.

  3. What would the distance of a cluster be with a distance modulus of 0? Explain or show your work.

  4. Interstellar dust absorbs light, especially blue light, making stars look dimmer and redder than they really are. This has been accounted for in the standard stars, but not the pleiads. Explain how this effects the position of your pleiades data on your graph, and how that changes the distance.

Last Modified: 8/11/05

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