The Moon's Orbit: Worksheet #2

Fall 2011 ASTR 110L, Sec. 2 Name: ________________

Date Diameterd DistanceR
11-Sep 23:00 ____________ ____________________
13-Sep 23:00 ____________ ____________________
15-Sep 05:14 ____________ ____________________
17-Sep 05:38 ____________ ____________________
20-Sep 06:30 ____________ ____________________
23-Sep 05:52 ____________ ____________________
24-Sep 05:38 ____________ ____________________
26-Sep 06:00 ____________ ____________________
28-Sep 18:00 ____________ ____________________
30-Sep 19:08 ____________ ____________________
02-Oct 19:24 ____________ ____________________
04-Oct _____ ____________ ____________________
06-Oct 19:50 ____________ ____________________
08-Oct 22:32 ____________ ____________________
10-Oct 20:06 ____________ ____________________
11-Oct _____ ____________ ____________________
12-Oct 21:51 ____________ ____________________
15-Oct 06:21 ____________ ____________________
17-Oct 05:11 ____________ ____________________
19-Oct 06:17 ____________ ____________________
21-Oct 06:00 ____________ ____________________
23-Oct 06:00 ____________ ____________________
25-Oct 06:00 ____________ ____________________
Date Diameterd DistanceR
27-Oct 06:00 ____________ ____________________
29-Oct 18:22 ____________ ____________________
31-Oct 20:20 ____________ ____________________
02-Nov 22:08 ____________ ____________________
04-Nov 22:45 ____________ ____________________
06-Nov 22:22 ____________ ____________________
08-Nov _____ ____________ ____________________
10-Nov 22:50 ____________ ____________________
13-Nov 03:43 ____________ ____________________
15-Nov 00:44 ____________ ____________________
17-Nov 02:51 ____________ ____________________
19-Nov 06:00 ____________ ____________________
21-Nov 06:26 ____________ ____________________
______ _____ ____________ ____________________
______ _____ ____________ ____________________
______ _____ ____________ ____________________
______ _____ ____________ ____________________
______ _____ ____________ ____________________
______ _____ ____________ ____________________
______ _____ ____________ ____________________
______ _____ ____________ ____________________
______ _____ ____________ ____________________
______ _____ ____________ ____________________

INSTRUCTIONS

First, measure the Moon's diameter, d, on the Moon photos in class. Compared to the images we measured directly at the telescopes, these photos have been magnified 10 times; thus 1 cm in the photos is equal to 1 mm at the telescopes. This means you can measure image diameters in centimeters on the photos, and easily convert your results directly to the diameters measured in millimeters at the telescopes. For example, on the 11-Sep photo the Moon's diameter is 10.6 cm; if you had measured the diameter at the telescope that night you would have found 10.6 mm, so write `10.6 mm' for the Moon's diameter on that date.

Extra Credit: As you measure these photos, take time to look at them. Most of them are real, but a few are computer-generated. Can you spot the fakes? Underline the dates of images you think are computer-generated.

Second, copy the `Average diameter' values from Worksheet #1 to the `Diameter' column for the corresponding dates here. Fill in the actual times of your observations. (See me if you missed any of these observations.)

Third, once you have listed all the diameters, compute the Moon's distance, R, using the formula

R  =  D × (F ÷ d)

Here F = 1200 mm is the focal length of the telescope's main mirror. Since d and F both have units of millimeters, the ratio F ÷ d is a pure number — the units cancel out. In fact, this ratio is also the ratio of the Moon's distance to the Moon's diameter. So to get the Moon's actual distance, just multiply by the Moon's diameter, which is D = 3,476 km. You can round the result to the nearest 100 km.


Joshua E. Barnes      (barnes at ifa.hawaii.edu)
Updated: 22 November 2011
http://www.ifa.hawaii.edu/~barnes/ast110l_f11/moonorbit_ws2.html
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