Practical Exercises for AST101
The Changing Sun and Moon

Purpose

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 through late April. 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

Using any source you want, look up the times of sunrise and sunset for Stony Brook for a full year. You need not do every day of the year - once a week will suffice. 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. Beware of the switch to daylight savings time. See the notes below on making proper graphs and tables.

In your report, comment on the data. Does any of it surprise you? Note in particular the days of the earliest and latest sunrise and sunset, and the shortest and longest days. Why do they not coincide? When is the day 12 hours long? Why does it not coincide with the vernal and autumnal equinoxes?

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 8 observations over an 8-week period, and should try to obtain 10 weekly observations, 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.

In you report, comment on the apparent motion of the Sun along the horizon from week to week. If your data are good enough, you may be able to determine whether or not the apparent speed of the Sun's day-to-day motion along the horizon is constant. Comment on what you would expect to happen if you were to continue these observations for the entire year. Explain how these observations are related to Stonehenge, Medicine wheels, and other paleolithic obervatories.

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 February 10, 2005. 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 at least 8 weeks following the February new moon. It is important to plan to make your observations at the same time each night (to within 15 minutes).

You must make at least 8 observations over two months, but will be able to make much better sense of the data if you observe on every clear night. The moon will not be visible on all nights. If it is not note that fact and the time you looked for it. Make a summary table of your observations.

For each obervation, note where the moon is and its phase. Locate the moon by its direction (N, S, E, W) and its altitude above the horizon (use your fist at arm's length). Look for any regularity in the location of the moon, and for a relation between the location of the moon in the sky and its phase. Sketch the appearance of the moon and its position in your logbook.