Astronomy 101 Project: The Observations

For this project, you will be making observations of the Moon to determine its synodic and sidereal periods. "Synodic" refers to a time that is measured relative to the Sun. The synodic period of the Moon is the time it takes for the Moon to go from new phase to the next new phase (or full to full, etc.). Since Earth is orbiting the Sun, the synodic period of the Moon is not the same as the time it takes for the Moon to orbit Earth with respect to the background stars, which is called the sidereal period. The difference between the Moon's synodic and sidereal periods is roughly two days.

Purpose: You will be taking some simple measurements of the position and phase of the Moon over a six week period. From these observations, you will determine the synodic and sidereal periods of the Moon and summarize your findings.

Procedure: You will make observations of the Moon each week for the next six weeks. Ideally, make an observation of the Moon every day. The only stipulation is that observations must be at least 16 hours apart. You'll find that the more observations you can get in, the better your results will be once you reach the analysis sections of the project.

You can keep a record of your observations using this Word document. You can also print a copy of the data sheet.

In class, we learned the different phases of the Moon. Of particular use here is knowledge about the rise and set times for the major phases of the Moon. You should plan out your observations. After all, the Moon is not always up in the sky at 7 PM. On some days, you will be able to observe the Moon during the day. On some days, the Moon will only be up at night. Use your notes from class to plan out your observations. The Moon will be up in the sky for at least nine hours every day. You can use this fact to avoid having to observe in the dead of night or very early in the morning. A little planning will go a long way.

Now that you have planned out your observation, it is time to go out to look at the Moon. Observations can be done from any location from which you can see the Moon; you do not have to go to Parkland to make these observations.

For each observation you make, you must start by getting yourself oriented. Make sure that you can find the principal cardinal directions (north, east, south, and west). If you are having trouble with this, remember the following:
1) Champaign-Urbana streets are nearly all aligned north-south or east-west. You can use these to help with cardinal directions.
2) On a relatively clear night, you should be able to find Polaris. Remember that Polaris is near the North Celestial Pole in the sky.
3) During the day, remember that the position of the sun can be a guide in determining cardinal directions. The sun will be due south at noon (1 PM while on Daylight Saving Time). It will rise to the south of east and set to the south of west between late September and late March.

Once you are oriented to the cardinal directions, you will need to record the following information:

Date of the ObservationEstimated time since rise (hours)
Time of the ObservationEstimated rise time
Phase of the MoonActual Rise Time
Moon's position in terms of cardinal directions (NE, S, SSW, etc.) and altitude

The time of the observation and the location of the Moon are important in determining the estimated rise time of the Moon. If you are observing the Moon close to the horizon in the eastern part of the sky, the Moon has recently risen. If the Moon is due south, it will have risen approximately six hours earlier. If the Moon is setting in the west, it will have risen approximately twelve hours earlier. Estimate the rise time of the Moon as accurately as you can for each of your observations. Remember that you can also use your class notes if you need help estimating the rise time of one of the major phases.

For the actual rise time, you can find this information on any weather website (look for "Astronomy") or the United States Naval Observatory website. If the time of moonrise is after the time you observed the Moon, the rise time would be from the previous day.

Record as many observations as you can for each week. The last day of the week is the due date to submit your observations. If you make observations when you don't have your data sheet, record them somewhere else and transfer them to your data sheet as soon as you can. You can also submit your data sheet using the appropriate dropbox on Cobra.

Each week of observations is worth five points toward your project grade. Be sure to get the observations turned in on time to get full credit. You will be expected to get a full set of observations if that is possible. If it has been a particularly cloudy week and you couldn't get three observations, just turn in what you have. You will not be penalized for inclement weather. However, do remember that if it is clear enough during the week to get in at least three observations, you will lose points for missed observations.