Astronomy 1L (Lab Class) Information
Observing the Motion of the Moon
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(preliminary version, essentially as posted April 21, 2012)
Not to be confused with the semester-long Moon Project
      You should be done with observations of the motion of the Moon over the last few weeks, because it is now at New Moon, and not visible. Starting Monday or Tuesday the Moon will be up in the very early evening somewhere in the West, and over the following week will move through the same area (Taurus, Gemini, Leo, Virgo, etc) that it went through a few weeks ago. You should observe its position relative to the stars in those constellations as accurately and as often as you can through the day before the project is due (April 30 or May 1, depending upon the class you are in). In other words, if the weather cooperates you will be doing another half dozen or so observations of its position.
     To turn in a report, collect all your observations of the Moon's position in chronological order, with your name and the date of the observation on every page, and with each page numbered as 1 out of so many, 2 out of so many, 3 out of so many and so on, where "so many" is the total number of pages of observations. All these pages and a "cover" page should be stapled or paper-clipped together, so that they should stay together; but the names, dates, and numbering should ensure that if the pages somehow become separated I can properly reassemble them prior to assigning a grade.
     The "cover" page should also have your name on it, and a map covering the entire page, based on one of the maps in chapter 3 that shows the stars and constellations near the Ecliptic (the path of the Sun, and the approximate path of the Moon) from Pisces and Taurus in the West, through Leo and Virgo in the East (in other words, all the constellations visible during the early evening). On that cover page you should indicate the position of the Moon on every single day you observed it, using the position shown on the date of your original observation. If it becomes obvious to you that some of your original observations are "off", do not correct them in plotting their position on the cover page. I want that page to show what your original observations recorded, not what the actual motion of the Moon was like.
     For part of the cover page "map" of the Moon's motion you will have "pairs" of observations separated by about 4 weeks, for which the position of the Moon is almost identical. For those pairs, compare the position of the Moon on the later date to the position on the earlier corresponding date, and note the difference in days between the corresponding observations. If pairs are separated by 27 days, note that number. If they are separated by 29 days, note that number. That number represents the approximate orbital period of the Moon around the Earth (and the background of the stars), but is not necessarily the exact value for the orbital period. To see what the exact period is, you will have to estimate whether the later observations are in about the same place as the earlier ones, or a little ahead of or behind the old ones (ahead of meaning that they are further to the east than the old ones, behind meaning that they are further to the west than the old ones). If they are in about the same place, then the number of days you already wrote down is your best estimate of the Moon's orbital period and should be labeled as such. But if the newer observations are ahead of or behind the older ones, then the actual period is a little less (if the newer observations are ahead of the older ones) or a little more (if the newer observations are behind the older ones) than the number you wrote down. For instance, if the newer observations are about a third of the way from the older observations to the next date for the older observations, then the orbital period is about 1/3 of a day less than the number you wrote down.
     Some of you should be able to use the discussion in the previous paragraph to figure out the orbital period of the Moon without any further input on my part; but some of you may need an illustration or two to help you figure out the answer. For that reason I will post a picture or two and captions showing how they would be used ASAP.