Regular Lab Night. U = E - M and P = E + M

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Miles Maximilian Greer
5 years ago
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1 Name Eclipse Lab: Regular Lab Night Watching a Lunar Eclipse Observations of eclipses were one of the keys to ancient astronomy, and today you will observe the oon as it is eclipsed by the Earth. Eclipses come in two types, solar and lunar. Solar eclipses happen when the oon passes between the Earth and the and blocks the rays of the. Because the oon is much smaller than the Earth, it can only block the light of the for part of the Earth. Earth oon The oon s shadow has two parts, the umbra, where the light of the is completely blocked, and the penumbra, where the light is only partially blocked. Observers in the umbra see a total eclipse, those in the penumbra see only a partial eclipse. Because of a curious coincidence of astronomy, the umbra forms a cone whose tip is very near the Earth. This implies that only a very small portion of the Earth gets to see any given total solar eclipse. Lunar eclipses occur when the oon passes through the shadow of the Earth. Like the oon s shadow, the Earth s shadow has both an umbra and a penumbra. When the oon passes completely within the umbra, as it does tonight, we get a total lunar eclipse. Note that near the oon, the umbral shadow of the Earth is smaller than the Earth, while the penumbral shadow is larger. Because of the coincidence mentioned before, it is possible to relate the sizes of the umbra and penumbra as they pass near the oon. These relations are given by U = E - and P = E + where P, U, E, and are the diameters of the penumbra, umbra, Earth, and oon respectively. Because it is difficult to see the boundary of the penumbra, we will use the diameter of the umbra to estimate the relative size of the Earth and oon. Earth oon

2 While we are observing the eclipse, which will stretch from around 10:30 until well past midnight, you will also be observing other astronomical objects such as ars. Information about using the telescopes can be found under Outside Lab 2. Exercises: 1. At approximately 10:30, sketch the oon on one of the provided circles (note the time on the sketch). Note in particular if the oon seems uniformly illuminated, or if one side vs. the other is brighter or darker. Any sign of non-uniformity of illumination indicates that the oon is already in the Earth s penumbra. Comments/Observations:

3 2. While Time: you are waiting to make your second measurement, use the provided telescopes to observe details on the oon s surface. Comments: 3. At about 11:00, make your second sketch of the oon on the circle provided. Note the shape of the Earth s shadow on the oon. Draw the shape of the light/dark boundary as carefully as possible. 4. You are seeing the shadow of the Earth on the oon. Based on your observations, what can you conclude about the shape of the Earth? Comments: 5. While you are waiting to make your third measurement, use one of the telescopes provided to examine ars and any other objects indicated by your instructor. Carefully sketch any details that you can see. Sketches/Comments:

4 6. At about 11:30, make your third sketch of the oon on the circle provided. Again, pay particular attention to the shape of the boundary of light and dark. 7. We are now going to estimate the angular size of the oon (the entire oon, including the dark portion). To do so, hold up a set of calipers and close/open them until the oon seems to be just held in the calipers. Simultaneously, have your partner measure the distance from the calipers to your eye. According to the small angle formula, the angular size of the oon (in radians) is just the separation of the calipers s divided by the distance d from your eye to the calipers. s d The units of s and d must be the same (I recommend millimeters). After one of you has held the calipers while the other measured the distance, trade places. Recalculate the angle, and average your results to decrease the errors. s 1 = d 1 = 1 = s 2 = d 2 = 2 = ave = 8. Using the transparencies provided by the instructor, attempt to measure the relative size of the Umbra and the oon using your second and third drawings. Average them together to get a more accurate number. The ratio we are measuring is R U E E 1 R 1 = R 2 = R ave = 9. Using the fact that the Earth is 12,800 km in diameter, find the diameter of the oon using = E/(R+1). E = R 1 =

5 10. Since we know the size of the oon (from part 9) and the angular size of the oon (from part 5), we can get the distance to the oon. According to the small angle formula, the distance to the oon D is related to the size of the oon and the angular size (in radians) by the formula D Rearrange this formula to find the distance D to the oon. The correct distance is 352,000 km. Find your percent error. What do you think contributed most to this error? D = Dactual Dmeasured = error = = Dactual Answer: 11. At 12:00, sketch the final picture of the oon. Why do you think you can see the portion of the oon that is in shadow? Does this region have any distinctive coloration to it? What type of light can best penetrate a lot of the Earth s atmosphere (hint: what color is the at sunset)? Can you account for the color of the oon? Answers:

Name: Partner(s): 1101 or 3310: Desk # Date: Eclipses. Purpose

Name: Partner(s): 1101 or 3310: Desk # Date: Purpose Eclipses Describe the orbit of the Moon Explain the differences between the types of solar eclipses Explain the differences between the types of lunar