AST 208 Semester Projects

I thought it might be worthwhile giving a few reminders and suggestions for writing up your semester projects. Let me begin with the moon project, since that involves the greatest number of students.

1. The goals of the moon project are to derive estimates of the synodic and sidereal periods of the moon using your own observations. The synodic period is how long the moon takes to go from one phase back to the same phase (i.e., full moon to full moon, or

first quarter to first quarter). The sidereal period is the time the moon takes to return to the same place in the sky with respect to the background stars and is the true orbital period of the moon. The data you have on hand are your markings of the location of the moon with respect to the stars on the star chart, plus your notations on the phase of the moon at those particular dates and times.

Your writeup should cover the following areas:

i. Include a paragraph or two of introduction, stating the purpose of your observations.

ii. Include a paragraph or two concerning how you carried out your observations, discussing any problems that you encountered along the way.

iii. Include a summary of your observations. This should at least be a list with the Universal Time date, the Universal Time (add 5 hours to EST or 4 hours to EDT, changing the date accordingly if necessary), the phase of the moon, and a note on where the moon was located in the sky (i.e., Sickle of Leo). You may include sketches or your sky charts with the position of the moon plotted if you think it would be helpful.

iv. Use your observations to determine the sidereal and synodic periods of the moon. Describe how you derived your results. Estimate the uncertainty of your values.

v. Compare your results with the actual values of 27.3 days (sidereal) and 29.5 days (synodic). Comment on whether the differences are consistent with your error estimates. You should always be guided by your observations, not by what you “know” the right answer should be.

2. Those of you who have been photographing the planets will need to use the star images surrounding the planets to determine the right ascension and declination of each planet you observed on the various dates of observation. I can show you how to do this, so you may want to stop and see me sometime soon. You will then be able to compare your positions with the predicted positions of the planets, using epemerides available on the web.

3. If you have been observing a variable star, your writeup should include the following steps:

i. Identify the variable you observed and tell which chart you used in making your estimates of the brightness of the variable. You should state how you made your observations (naked eye, binoculars, etc.) and what comparison stars you used.

ii. You next need to report your observations. Give the date and time of each observation. Here it is convenient to turn the dates and times from Universal Time to Julian Dates. The Julian date is a calendar system that just counts days. You can use the calculator at

http://wwwmacho.mcmaster.ca/JAVA/JD.html

to turn your universal time dates into Julian dates, which are convenient for doing calculations. Then give the magnitude you estimated for the variable star. You may want to add a comment if some observations were more uncertain than others.

iii. Then you want to use your observations to make a phased light curve. If you have a large number of observations, you may try to calculate the period of the variable star on your own. If you do not have that many observations, you can use a period from the literature (be sure to state your source). To calculate the phase you take the Julian date and divide by the period. Just as an example, say you have a period of 5 days and a Julian date of 17.5 (your real JD will be much bigger). 17.5/5 = 3.5. Just keep the part after the decimal point, 0.5 in this case. That is the phase. Now if you plot your estimated magnitudes versus phase, you will be mathematically folding all of your observations into a single light cycle of the star. When you plot magnitude versus phase you have the “phased light curve”.

iv. Comment on how well your observations match your expectations. How accurate do you think each of your magnitude estimates is?

4. Some of you are making telescopic observations of the moons of Jupiter. A goal here is to see whether, from your own observations, you can determine the orbital periods of the different moons. A difficulty is telling one moon from another. If you get stuck, you can use the java utility on the sky and telescope website to tell you which moon was which at the time that you observed:

http://skyandtelescope.com/observing/objects/planets/article_830_1.asp

Once you estimate the orbital periods from your own observations you can compare them to the known orbital periods. As with the other projects, you will want to include a list of your observations, perhaps with sketches of the relative positions of the moons with respect to Jupiter. If you get ambitious, you can see whether your results indicate that the moons obey a form of Kepler’s third law.

If you are doing a different semester project, you’ll have to devise a reporting scheme of your own. Remember to report all relevant observations and include estimates of uncertainties where appropriate.