Astronomy Lab
Observing Variable Stars
Name ______________________
Introduction: In this activity, you will estimate the magnitude of a variable star, determine its
light curve and do an analysis of magnitude, range, and period measurements.
Your completed report should include this sheet with your calculations AND the graph of W Cyg
magnitudes with an estimated light curve sketched on it.
Part I. Magnitude Data
Complete the chart below by making estimates of W Cyg in class:
Day Magnitude
0
24
82
116
144
156
178
Part II. Plotting a Light Curve
Use the graph paper provided to plot your estimated magnitudes and sketch a light curve for W
Cyg. If you prefer, you may generate a graph using Logger Pro. The advantage of Logger Pro is
being able to use the curve fitting options.
Determine the length of one period of variability to the nearest day. Record your answer
below, and explain how you calculated it.
Experimental period of W Cyg ________ How calculated:
Next, determine the change in magnitude (range) and enter it below. Remember to use the
curve, not the actual data points for this procedure. Use 1 decimal place in your answer.
Example: 1.3
Experimental range of magnitude _______
Using data from the entire class, we will together determine the light curve and range of W Cyg.
Record the class values below:
Class period of W Cyg:
_______
Class range of W Cyg: _______
Part III. Statistical Analysis of Data
Calculate the error in your measurements and in the class measurements of W Cyg and report
the values below. Show your calculation set-ups for full credit! Express your answer to the
nearest 1%.
The historic values for W Cyg, derived from observations reported to the AAVSO are:
Period = 131.1 days
Magnitude range = 1.5
Percent Error = (experimental value - AAVSO value ) x 100
AAVSO value
Period Error (%)
Range Error (%)
Your error
___________
____________
Class error
_____________
____________
Part IV. Questions
1. The error measurements for the class values of data and light curves of W Cyg are
usually better than an individual’s error values. Why?
2. What type of magnitude scale is used in this activity, apparent or absolute?
3. Suggest one mechanism that would cause a star to have a variable magnitude.