Bates College

Astronomy/Geology 110


Lunar and Planetary Science

OBSERVING


It is expected that through the semester you will keep a journal in which you record your observations of the sky. Since the primary purpose of this is to develop some feeling for how things change with time, your journal will only be good if you look at the sky frequently. The weather in the winter in Maine is not always clear! Hence you should plan to observe the sky at least briefly at every opportunity! Develop the habit of looking up at the sky every evening as you exit Commons, and if it is clear, plan to spend a few minutes observing. On most such evenings you can expect to find me out with a telescope on the Carnegie porch, so stop by.

The worst thing you can do is to do no observing until the last week of the semester. You will never have enough observations to understand how things behave. And it will be just your luck that the whole week will be cloudy. It is fairly traditional in astronomy to play pool when it is cloudy, and most major observatories have a pool table. Hanging on the door of the pool room of the Mount Wilson Observatory is a cartoon figure of a skeleton playing pool. The caption reads "Waiting for the Weather to Clear". You get the message? "It was cloudy" will not be considered an acceptable reason for having no observations! You can assume that I will know what nights are clear.

Furthermore, all observations recorded in your journal should be YOUR OWN! I expect that you will observe in groups, and I strongly encourage that, but before you write something or draw a sketch in your journal and date it, you make sure that YOU HAVE SEEN IT YOURSELF! Then and there! I will supply you with an affidavit form certifying that all observations in your journal are your own. Copying observations from another person's journal or making up data are serious lapses of scientific integrity equivalent to cheating on an exam. An honest journal with a small number of observations is always better. Enough said!

Right now you are probably asking yourself, But what should I observe? Here is a basic list. Other things might be added from time to time during class discussions. You should use the journal for this class which is available in the bookstore, as it provides LOTS of guidance for observing. The list below is only a brief summary.

THE STARRY SKY You should notice the way the stars appear to move as you see them in various directions. You should be able to measure the time it takes the stars to seem to go around once. You should be able to figure out where the "pole" of the stellar motion is. You should understand where the "equator" and "ecliptic" are in the sky and what they mean. You should understand the motion of the SUN through the background of stars. You should be able to interpret your observations in a system in which the stars are fixed in space. This will take a while, so you should start right away!

THE MOON You should observe the Moon whenever you can see it, and ask yourself the following questions, and record your answers:

1. What direction do I look in to see the Moon NOW? (East, South, West, North?...) How high above the horizon is it? What is the relation between the direction I look and the elevation of the Moon above the horizon? Can I draw a path through the sky which is followed by the Moon? (It will take a number of observations of the Moon before you can answer the last questions.)

2. How is the Moon oriented in the sky? Where is the "north pole"? What is the relationship between the orientation of the Moon and its position as observed in question 1? What does this say to you about how the Moon moves?

3. What is the PHASE (crescent, full, etc) at any given time? What is the relationship of this phase to the relative positions of the Moon and the sun? How can you interpret this in terms of the motion of the Moon, Earth, and sun? Where does the Moon get its light? Do not fail to include observations made in the morning and through the day.

4. How fast does the Moon move compared with other objects? Some evenings you will observe the Moon close enough to another object (star or planet) that you will be able to see relative motion. Watch the sky long enough to do this. How long does it take the Moon to move its own diameter with respect to other objects?

5. Where are the objects on the "selenography" list found on the Moon? You should be able to locate the "maria" by just looking up at the Moon. With a telescope, you should be able to find the large craters and other objects. Draw your own sketch map of these things while using the telescope.

JUPITER You should observe Jupiter whenever you can see it, and ask yourself the following questions, and record your answers. Throughout the semester you will be able to view Jupiter in the evening sky, although at the beginning it will rise fairly late. You should understand why the time of rising gets earlier through the semester.

1. Where is Jupiter in the sky with respect to the sun? How does that change through the winter? Can you describe the cause of this change?

2. If Jupiter is close to other visible objects, draw a map of the relative locations early in the semester. Do this again later in the semester. Has Jupiter moved with respect to the stars? You might need a telescope to do this.

3. With a telescope, note the position of the "north pole" of Jupiter and relate it to the path Jupiter follows through the sky, as for the Moon. You can think of the stripes on Jupiter as being like parallels of latitude.

4. With a telescope, observe the four bright moons of Jupiter. Note their positions with respect to each other, Jupiter, and Jupiter's stripes. Draw a sketch map of these positions. When possible, check after a couple of hours and see how the moons have changed positions. After many observations try to determine which moon is which- Galileo did this. If you observe the moons regularly, you might get to where you can see slight differences in color. Very occasionally, it is possible to see a black spot on Jupiter which is the shadow of a moon!

SATURN You should observe Saturn whenever you can see it, and ask the same questions as for Jupiter, except that you are not likely to see many of the moons, but you CAN note and sketch the RINGS. One moon of Saturn is so bright you should be able to watch it over several weeks and determine its orbital period. Throughout the semester Saturn will be visible in the early morning before sunrise.

MARS Throughout the semester Mars will be visible in the very late evening and relatively close to Saturn, rising first at midnight and then gradually earlier. You should come to understand the reason for this motion. Perhaps you will be able to see a polar cap with a telescope. You should observe and plot Mars on a number of occasions to see how rapidly it moves across the background of stars.

VENUS A week into the semester, Venus rises an hour or so before the sun, and gradually earlier, so you might see it in the east early in the morning. Observe Venus with a telescope several times. Draw a sketch map each time of the shape that you observe. Can you interpret your observations?

MERCURY Through early February it should be possible to see Mercury just after sunset, and in early March it should be possible to see it just before sunrise. Try to observe this elusive planet which many people never see in their whole lives.

URANUS and NEPTUNE In the early winter, these distant planets set after the sun. It would be difficult, but you might try to observe them, and describe their appearance and how it compares to the appearance of faint stars. Uranus is bright enough to see with the "naked eye" in a very dark place, but the campus does NOT pass this test.

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