Practical Exercises for AST101
The Changing Sun and Moon


Astronomy is an empirical science. That means that all we know is based on observations. Nothing is true because a book or your professor says so. It is true because you can check with your own eyes or some apparatus that it is true. To experience the flavor of what scientists do, and show you that some of the things you learn can be easily checked with your own eyes, you will do some observations of your own. You will make measurements, describe them in sketches, graphs, and words, and draw conclusions from them.

The success of science depends on the integrity and accuracy of all the observations that are reported. No falsifications or deliberate misrepresentations of observations can be tolerated without destroying the very foundations of science.

Note 1: we have in the recent past had quite a bit of trouble with reports of observations that were never made, reports copied from others, and other cheating. Any such behavior will be reported to the Academic Judiciary and leads to the award of a Q grade, as well as severe grade penalties in the course. See below for details.

Note 2: All the activities require regular observations on dates throughout the 7-week period from September 10 to October 26. It is impossible to make up for lost work if you do not start in time, you must work on it regularly.

Description of the Activities

Your work consists of three separate activities. You must do all three.

Activity 1: Times of Sunrise and Sunset

For a 7-week period starting on approximately September 10, check the newspaper (Newsday, NY Times, etc., but do not mix the sources) for the times of sunrise and sunset on a given day, once a week (best if done the same day each week). Calculate for each of these days the length of daylight and an approximate time for astronomical noon, by taking the time midway between sunrise and sunset. You may obtain the times of sunrise and sunset from other sources such as web pages. In any case, report the source you used.

Make a table in which you list for each date the times of sunrise and sunset, the length of day, and the time of astronomical noon. Also make four graphs, one each for sunrise, sunset, length of day, and time of astronomical noon, to show how this quantity changes with date. See the notes below on making proper graphs and tables.

Activity 2: Location of Sunset

Pick a place where you can see the western, southern, and eastern horizon and the sunset, and where you can return regularly during the semester. Good places are those with few obstructions (e.g., pastureland, or sports fields) or the top of a building that is taller than most around it (e.g., the top of the Earth and Space Science building). Make a sketch of the horizon, with the major landmarks you see on it: trees, power line poles, buildings, etc. (Further details, hints, and requirements on the sketch are given below.)

Once or twice a week note where the sun sets on your sketch. (Yes, Long Island weather is lousy, but there is almost always at least one clear sunset a week.) Be sure to record the date and time of each observation in your logbook, as well as the sunset location and the circumstances of the observation. You must make at least 7 observations over an 7-week period starting about September 10, spread as evenly as possible (weather permitting). Make a summary table of your observations. Where you see the sun relative to landmarks depends, of course, on where exactly you stand. Especially for nearby landmarks this makes a difference, so do note where exactly you observe from to within a few feet, and return there each time.

Activity 3: Location and Phase of the Moon

The Moon has provided a constant source of interest and inspiration over human history. Its day-to-day movement through the heavens is so common as to escape notice. This activity will involve documenting the Moon's motion through a month.

The moon will be new on September 17 and October 16, 2001. If the sky is clear it will become visible as a crescent a few days after new moon. The purpose of this activity is to record the Moon's appearance and location in the sky over a period of about two weeks following the September new moon and 10 days following the October new moon. It is important to plan to make your observations at the same time each night (to within 15 minutes). Choose a time between 7 and 10pm. If you observe close to sunset, you can start seeing the moon 1 day after new moon. Roughly for each hour later, you have to wait an extra day before starting. In the first period, continue for 2 weeks after your start time. For example, on Sept 17 the sun sets at about 7pm. If you choose 9:30pm as your observing time, 2.5 hours after sunset, you have to wait until Sept 19 or 20 to start seeing the moon. Then you have to continue your observing period until two weeks from then, i.e., until Oct 3 or 4. For the second period, there is no full 2-week period until the due date for the report on Oct 29, so stop on Oct 26 or 27 no matter when you started. You must make at least 6 observations (total over the 2 periods), with at least 2 in each one. Make a summary table of your observations.

More Detailed Instructions


A logbook is a note book in which an observer records in some detail all his/her activities. You should buy a small notebook especially for this purpose, and hand it in with your report. It is an essential part of your activity to keep a logbook, and it will determine part of the grade. In your logbook, you should describe accurately where you did the observations, and for each observation you make you should note the time, date, weather, results of your observations, and any further relevant information.

Here is an example logbook entry:

Example Logbook Entry
A good logbook entry is dated, and the pages numbered. Note the time and date are there, as well as a brief comment about the conditions. A part of the whole sketch for sunsets is roughly drawn, and enough measurements are in it to locate the sunset and transfer the observations later to the full sunset sketch. The observing site is not described, but it is noted where the description can be found. Deletions are fine, it is a work in progress, but make them clear so there is no doubt what you meant to keep and what not.

Accuracy and care in observing

Because science is based on the premise that what we see is always true, and takes priority over theories, we can only do science and understand nature if we can be sure of reported observations. Therefore, scientists have high standards of what is an acceptable observation. You only report seeing the sunset if you really saw the Sun set. If it disappears behind a cloud bank a while earlier, too bad. Do not guess where it might have set. If you guess anyway and get it badly wrong, then you report an impossible observation, and such carelessness is scarcely better than completely making it up: both are fraud, and treated as such. The same is true for the Moon: the Moon is not always up at night, and may be behind clouds, so if you cannot find it you are probably right: it must be below the horizon or behind a cloud. Again, you know very well what the Moon looks like, so you know when you saw it and when you did not. If you didn't see it, don't report seeing it.

Sketches of the Horizon

Your sketch of the horizon should be at least the size of a sheet of legal paper (8.5 by 14 inch). Use it with the long side parallel to the horizon. Use separate sketches for your sunset observations (where the sketch only needs to cover about 60 degrees centered on west) and the Moon observations (where it needs to cover more than 180 degrees, from northeast via south to northwest). Mark West, South, and East on your map, either by using a compass or by determining West from the location of sunset on the first day of autumn (September 22, 2001). Note: You should put all your sunset observations into the same sketch. Also put all your moon observations in one sketch. See Bennett's book, figure 2.10 on page 45, on how to measure angles with your hands. In each sketch, measure four angular distances between pairs of landmarks of your own choosing, and mark these in your sketch. Make sure the values range between 3 and 30 degrees for the sunset, and between 20 and 120 degrees for the moon sketch.

Example Moon Sketch
Sketch for the moon observations. Note the horizontal line for the horizon, the clearly indicated and named landmarks, and the marks for East, South, and West on the horizon. Each moon position is drawn with the phase as observed and labelled with the date of observation (Note: the set of observations as shown is not correct!). Make sure you also put the moon in the correct direction and height above the horizon. Draw the horizon about 1/3 of the way up, and let the top of your sheet correspond to an altitude of 80 degrees.

Example Sunset Sketch
Sketch for the sunset observations. Note the horizontal line for the horizon, the clearly indicated and named landmarks, and the marks for West on the horizon and for the scale. Each sunset position is drawn as observed and labelled with the date of observation (Note: the set of observations as shown is not correct!).

Good Tables

A good table lists all information clearly, aligns information neatly in columns that are clearly separated from each other. The rows are also neatly aligned, and the columns have headers that say what is in the column.

Here is an example of a good table:

Example Good Table
Note the table number and descriptive but short title. Note the headers describing the quantity in each column, and the unit in which it is measured. Note the alignment of the numbers in the columns.

Good Figures

A good figure has tickmarks and labels on the X and Y axis. The tickmarks are equally spaced and whatever quantity is plotted changes by equal amounts at each tickmark. Each axis carries a label that indicates what is plotted there. All marks are large enough to be read easily. Symbols in the graph are big enough to be clearly visible. Also, the length of each axis is chosen so that all the data fits on and not too much space is left. CAUTION: If you are using some computer program (like a spreadsheet) to make your graphs, do not assume that it will get these things right automatically. Often, it will not.

Here are examples of what to do and what not to do:

Example Bad Graph
Note the lack of clear axis labels, the unequal spacing of labels on the horizontal axis, too small plot symbols, lots of wasted space because the range of the vertical axis is much larger than needed to accommodate the values in the graph.

Example Good Graph
Note the labels on each axis, which specify what is plotted and in which units. Note the large symbols, and note that the range of values along each axis is well matched to the values actually in the graph: everything fits in, and there is not too much empty space.

Requirements for your report

To complete the practical assignment, you must hand in the following:

  • Logbook: This must contain the raw results and notes of all your observations, as well as the calculations and manipulations you performed to get the final results. Without it, the report will be returned ungraded, and a grade of zero given for the work.

  • Report: In the report, you describe the results of your observations, illustrated with graphs, tables and sketches where required and/or appropriate. The report should be scholarly: neat and legible, with correct spelling and grammar. (Note that this not require that it be typed, but make sure your handwriting is clear.) Use plain and clear language. The report need not be long, 3-5 pages of pure text (excluding graphs, sketches, tables) should be enough, and less may be possible if your writing style is especially clear and crisp. Note that all the final tables, graphs, and sketches must be in the report. Do not refer to raw versions in the logbook.

  • Academic Honesty Statement: You will be given a statement declaring that your report satisifies the requirements of academic honesty (see below). You will print your name and ID on this, sign and date it, and staple it to the front of your report. You will be given a copy with the handout, but you can already see it here. Without it, your report will be returned ungraded, and a grade of zero given for the work.

    Academic Dishonesty

    In the recent past, we have had considerable difficulty in both AST101 and AST105 with academic dishonesty in the practical exercises. Anywhere between 10 and 30 students per course per semester were caught copying (parts of) reports from friends or doing (parts of) the assignment in groups, or making up and/or looking up observations in books or on the web, and then trying to pass these off as their own work. As always, these violations of honesty are also violations of University rules. They are invariably reported to the academic judiciary. Students so reported will receive a grade of Q on their transcript, unless they appeal the accusation successfully. Fortunately, such transgressions are very easy for us to find and prove, and as a result I do not know of any recent case of an accused student being found not guilty at a judiciary hearing involving the practical exercises for astronomy courses.

    While I am absolutely determined to punish any case of academic dishonesty that I find, it is very unpleasant to have to do so. It is much better to avoid even the semblance of wrongdoing and have no cases to report. Let me, therefore, state very clearly what I expect and give some examples of what I (and the judiciary) consider to be dishonesty:

    Should you have any remaining doubts about what is allowed and what is not, please come and talk to me for clarification. You may also visit the web site of the Academic Judiciary, at for more information.