Name:________________________________

ID number:____________________________

Lab Sheet: Using Cepheid Variable Stars to Measure the Distance to a Nearby Galaxy

I. Find the Cepheids!

A. Record all the grids you visited: 

  26
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B. Cepheid information

Find a minimum of 8 Cepheids. 
Cepheid name   Grid #   Avg mV   P(days)    Mv     mV-Mv
____________   ______   ______   _______  ______  ______ 
____________   ______   ______   _______  ______  ______ 
____________   ______   ______   _______  ______  ______
____________   ______   ______   _______  ______  ______
____________   ______   ______   _______  ______  ______
____________   ______   ______   _______  ______  ______
____________   ______   ______   _______  ______  ______
____________   ______   ______   _______  ______  ______
____________   ______   ______   _______  ______  ______ 
____________   ______   ______   _______  ______  ______

C. Other objects of interest:

Grid #   (x,y)coordinates                Comments

  26        178, 113         Blip in lower right section
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II. The distance to M100

A. The P-L relation

Calculate the absolute magnitudes for each Cepheid in Part I, Section B using the equation 

    MV = - [2.76 (log10(P) - 1.0)] - 4.16,

where P is the period of the Cepheid in days from column 4. Enter your results in column 5.

B. The average distance modulus

Calculate the distance modulus (mV-Mv) for each Cepheid in Part I, Section B and write your results in column 6.

Sum all the distance moduli and divide by the number of Cepheids to get the average distance modulus. 

    Average distance modulus: mV-Mv =  __________

C. The distance to M100

Calculate the distance to M100, using the average distance modulus in the equation 

    d(pc) = 10[0.2(mV-Mv+5)]

    d = __________ pc,      or      d = __________ Mpc.
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