II. Assignment:
NOTE: Everything must be typed for this lab with the exception of your drawings and graphs and observational notes. Combine everything into one single document, inserting any photos.
PRE-LAB QUESTIONS:
Using the information above, answer the following questions (must be typed), making sure to have everything in your own words and put your explanations in complete sentences.
List some of the factors that could affect an asteroid’s brightness.
How is the light reflected off of an asteroid?
How would the brightness of light from an asteroid depend on its orbit around the Sun?
How does the position of the Earth, relative to that of an asteroid, affect the asteroid’s apparent brightness?
In addition to moving in its orbit, what other motions might an asteroid undergo that would affect its apparent brightness.
ACTIVITY:
Procedures:
Set up (Potato #1 round):
Establish a work area that has a dark background or place a dark piece of paper to be your background.
Spear your spherical/round potato onto your fork. (Something that might also work is to cut an apple in half and using two toothpicks you can place the potato on top of the apple.) Spear your potato in such a way that it goes through the center of mass and is as balanced as possible.
Place your light source so that it shows on the potato
Position yourself so that you see the potato as in the above image, you being on the same side of the light source, with your paper and pencil. Note: Be sure to keep your light source in the same position at all times, simulating the sun.
For your drawings in step (f.) you are going to treat the potato like a “clock” and rotate it 4 times, 90 degrees each time (so that it is at 00, 15, 30, 45 min past the hour). You want to make sure that you observe it from the same level vantage point, from your light source, each time. This is where it might be helpful to have a friend/helper rotate the potato, so you can remain stationary as it rotates.
Using the Lab Worksheet (which must include your handwritten signature and date on your drawings of your potato): Take an image of your potato in the 1st position, along with your ID card that has your name, signature and date on it, to be inserted into your lab report. Carefully observe the potato going through a few rotations. Make a note if you can see a change in the amount of visible surface area as it rotates. In the four squares on the worksheet, draw your spherical/round potato in the four desired positions. Try to include any shadowing or “craters”/indentations that you see.
In the Observation Notes under the four boxes – type a description of anything you notice, especially noting if the visible surface area changed as the potato rotated. For example, your answer might be similar to the statements: “It didn’t change at all,” or “It gets bigger then smaller,” etc. Also, make a note as to whether you saw any periodic or repeating features, i.e. peaks and valleys that repeated or not. (After a rotation or two).
Set up (Potato #2 horizontal position):
You are going to repeat the process above, but now with your elongated potato. Place the potato horizontally (long-side down).
Repeat all of the above steps including taking an image of your potato (along with your ID card) in the 1st position and filling in the Worksheet drawings and making any observation notes.
Set up (Potato #2 vertical position):
You are going to repeat the process above, still with your elongated potato, only now place the potato vertically (short-side down).
Repeat all of the above steps including taking an image of your potato (along with your ID card) in the 1st position and filling in the Worksheet drawings and making any observation notes.
Graphing: For each of the three set-ups above, you will create a graph that shows how the amount of visible surface area changed as the potato rotated. Think about what a graphical sketch of fraction (or percentage) of visible surface area (y-axis) vs. time (x-axis) would look like for each potato set-up. Keep in mind that the maximum percentage of surface area that you can observe while seated in front of the potato is approximately 50%, i.e. you cannot see the back of it. See the illustration below of the axis system and of a sketched graph. This sketch may or may not be similar to the ones you deduce from your observations. Note: On your graph, include the four points that you come up with for each of your drawings and then try to connect them with a smooth line as shown below. Use the worksheet provided, but still make sure to label your graphs. Scan or take a clear photo of your worksheet to insert into your lab report. Now, we’ll test your hypothesis.
POST-LAB QUESTIONS:
Using the information above, answer the following questions (must be typed) and in complete sentences.
The sketches that you have created are very similar to the light curves graphed by astronomers. In this case light reflected from an asteroid is measured electronically and the amount of light reflected (called the amplitude of the reflected light) is graphed against time. Explain in your own words how you think such measurements can give astronomers an estimate of the shape of an asteroid.
If an asteroid is observed throughout one complete rotation and its maximum brightness is three times as great as its minimum brightness, what can be inferred about the area of the largest side compared to the smallest side?
If astronomers happened to observe a carrot-shaped asteroid that is rotating around its long axis while its “north” pole (the stem-end) is facing Earth, what would the light curve for this asteroid look like?
In order to obtain a good estimate of the shape of an asteroid, it is necessary to observe light curves at different parts of the asteroid’s orbit. Explain why this is necessary.
If your Potato #2, the elongated one, were mounted at an angle of 45 degrees, to the axis of rotation, what do you think your sketch would look like?
How much more difficult would this activity be if you were observing your rotating potato from across the room or the length of a basketball court, or football field? How would these distances affect the accuracy and reliability of your observations?
How does the length of a football field compare with the distance between an Earth-bound telescope and an asteroid? What does this tell us about the need to possibly visit these objects and see them up close?
