Lab_2_Seasons_S24

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Apr 3, 2024

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Lab 2: Earth's Seasons Name: Group Name: Lab 2: Earth’s Seasons Submitting Today's Lab For today's lab, you'll be taking photos with your phone and including them as part of your work. For this reason, we request that you do not turn this lab in on paper, but instead submit it as an electronic file. However, during class, while working with the globe and taking pictures, we suggest that you use the paper version of the lab found in your lab binder to direct you in your work and scribble notes. When you are ready to fill in the electronic (word doc) version of this lab, go to D2L and find the link to "Template Word Doc for Lab 2". Download the file, and fill it in with typed answers and the pasted photos you took. Make sure you paste each photo into the document at the relevant prompt, as an answer to the relevant question—you will not get credit if you just attach a pile of miscellaneous image files at the end of your lab. When you are done working on the lab, save your file as a single pdf (with your photos embedded), and then upload it to Gradescope. Group Activity Set-Up With your lab group, collect your materials; you will need a globe and a ﬂashlight connected to a ﬂashlight stand. Find a relatively dark location in the planetarium auditorium or in the black-light hallway. Place the globe (which represents Earth) 4–6 feet away from the ﬂashlight (which represents the sun). Adjust the ﬂashlight so that it is centered on the globe, and parallel to the ground (or as close as you can get it). 1

Lab 2: Earth's Seasons You can turn the ﬂashlight on with the larger black button at the base of the ﬂashlight. There is a small silver button on the side of the ﬂashlight that changes the intensity of the ﬂashlight. You'll probably want to use one of the brighter settings. The division between day and night is called the terminator (see red arrow on the picture below). To best view the terminator, stand directly in front of it and take a few steps back. Do not focus on the reﬂection of the ﬂashlight If the globe is properly centered on the ﬂashlight, the terminator will be coincident with the line that extends up from the center of the base of the globe. There is one terminator on either side of the globe: one for sunrise and one for sunset. PART A - NORTHERN SUMMER SOLSTICE The northern summer solstice represents the time of year when the northern hemisphere is tilted toward the Sun; in your globe/ﬂashlight model, this corresponds to the time when the metallic brace supporting the globe is oriented toward the ﬂashlight. Orient the globe so it is the northern summer solstice. 2

Lab 2: Earth's Seasons A1. Consider New York City, USA and Los Angeles, USA. You probably know that sunrise occurs first in New York, and then a few hours later, it occurs in Los Angeles. In the evening, sunset occurs first in New York—and later it occurs in Los Angeles. Move these cities through each terminator reproducing (1) sunrise in New York, (2) sunrise in Los Angeles, (3) sunset in New York, and (4) sunset in Los Angeles. As viewed from the top down (i.e., north pole), is Earth rotating clockwise or counterclockwise? (1 point) A2. Now locate New York City, USA and Santiago, Chile. Note that they share approximately the same longitude (i.e., they are at similar points E–W on Earth), but New York is in the northern hemisphere and Santiago is in the southern hemisphere. Estimate the average longitude value of New York and Santiago. Note whether it is a west longitude (marked with a "W" on the globe) or an east longitude (marked with "E" on the globe). (1 pt) A3. On the northern summer solstice (June 21), how does the time of sunrise in New York compare with Santiago? Does it occur earlier, later, or at the same time in NY as in Santiago? Take a photo of your globe with your phone to illustrate your written answer and embed it here (Hint: it might help to show sunrise in New York, while also capturing the state of Santiago at that time). Be sure you describe what your photo is showing! Note that the format of your photo should be .jpg or .png; you may need to turn off live photos on your phone. (2 pts) 3

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Lab 2: Earth's Seasons A4. Repeat this same process for sunset on the northern summer solstice. Describe if sunset occurs earlier or later in NY, as compared to Santiago, and embed a photo of your globe that demonstrates this point (don't forget to explain how the photo illustrates it). (2 pts) A5. On the northern summer solstice, how does the length of day (when the sun is up) compare between New York and Santiago? (1 pt) Daytime is longer in New York than in Santiago. Daytime is longer in Santiago than in New York. Daytime is the same length in Santiago and New York. A6. On the northern summer solstice, there are some points on Earth where the sun does not rise and set. Give an example of such a place where the sun does not rise and set, and explain what happens to the Sun throughout a 24-hr solstice day at that location. Illustrate your answer with a photo. (2 pts) 4

Lab 2: Earth's Seasons PART B - NORTHERN WINTER SOLSTICE Now orient the globe so it is six months later, corresponding to the northern winter solstice (Dec 21). To do this, the globe and the ﬂashlight should now switch locations. Go ahead and do this if this lab is confusing you (keep the ﬂashlight pointing at and centered on the globe; in reality, the Sun puts out light in all directions, but our ﬂashlight model "Sun" only has a relatively narrow beam). Alternatively, you can simply rotate the globe apparatus by 180 degrees so that the North polar axis is tilted exactly away from the Sun. The globe's metal brace should now be oriented away from the ﬂashlight. B1. On the northern winter solstice, how does the time of sunrise in New York, compare with Santiago? Does it occur earlier, later, or at the same time in NY as in Santiago? Embed a photo of your globe with your phone to illustrate your written answer. (2 pts) B2. How does the time of sunset on the northern winter solstice compare between New York and Santiago? Embed a photo of your globe that demonstrates this point. (2 pts) B3. On the northern winter solstice, how does the length of day (when the sun is up) compare between New York and Santiago? (1 pt) Daytime is longer in New York than in Santiago. Daytime is longer in Santiago than in New York. Daytime is the same length in Santiago and New York. 5

Lab 2: Earth's Seasons B4. On the northern summer solstice, you identified a location where the sun does not rise and set. What happens to the sun at this location on the northern winter solstice? How is it different from the northern summer solstice? Feel free to include a photo to support your answer. (2 pts) PART C - EQUINOX C1. Now orient the globe so it is the equinox; either northern vernal (Mar 21) or autumnal (Sep 21) equinox is fine. Upload a photo showing this orientation, and describe what the photo is showing. (2 pts) C2. On the equinox, how does the time of sunrise in New York compare with Santiago? Does it occur earlier, later, or at the same time in NY as in Santiago? Take a photo of your globe with your phone to illustrate your written answer. (2 pts) C3. How does the time of sunset on the equinox compare between New York and Santiago? No need to include a photo, we just need a brief written answer here. (1 pt) 6

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Lab 2: Earth's Seasons C4. On the equinox, how does the length of day (when the sun is up) compare between New York and Santiago? (1 pt) Daytime is longer in New York than in Santiago. Daytime is longer in Santiago than in New York. Daytime is the same length in Santiago and New York. C5. On the northern summer solstice, you identified a location where the sun does not rise and set. What happens to the sun at this location on the equinox? How is it different from what happens on the winter solstice and summer solstice? Feel free to include a photo. (2 pts) PART D - ELEVATION ANGLE & CONCENTRATION OF SUNLIGHT In the previous questions, we have explored part of the answer to why it is warmer in summer than in winter. But this is only part of the story—you would think that with days that are 22 hours long during the summer, it would be hot in Alaska and northern Canada during the summer, but it is not (compared to say, the tropics). The other effect caused by Earth's tilted spin axis is the changing height that the noontime Sun attains during the various seasons. The Sun is highest in the sky at noon everyday. But how high is it? This, of course, depends on both your latitude and the time of year. For East Lansing, the Sun has an altitude of 71° on June 21st. On both March 21st and September 20th, the altitude of the Sun at noon is 48°. On December 21st its altitude is only 25°. Thus, the Sun is almost straight overhead at noon near the Summer Solstice, but very low during the Winter Solstice. What difference can this possibly make? We now explore this using the ﬂashlight, a protractor, and a measuring tape. 7

Lab 2: Earth's Seasons Turn on the ﬂashlight and hold it about 15 cm (6 inches) above the ground. Try shining it directly down at the ground: Then, try pointing the ﬂashlight at the ground at an angle: D1. How does the illumination pattern change with the angle of the ﬂashlight? Does the illuminated pattern appear to change in brightness as you change angles? (1 pt) 8

Lab 2: Earth's Seasons Now let's quantify this effect. Arrange the apparatus as in the 90° elevation illustration above. The illuminated spot should look circular. Measure the diameter of this circle using a ruler, and estimate the area of the circle. Recall that the area of a circle is ( 𝜋 D 2 )/4, where D is the diameter of the circle and 𝜋 = 3.14159. D2. What is the diameter of the illuminated circle? Give your answer in units of cm. (1 pt) D3. What is the area of the circle of light at an elevation angle of 90°? Give your answer in units of cm 2 . (1 pt) Now hold the ﬂashlight at an elevation angle of 45°, as in the 45° elevation illustration above. In this case, you'll be measuring the major axis and minor axis of the ellipse. The minor axis (b) is the smallest diameter, while the major axis (a) is the longest diameter of an ellipse. The area of an ellipse is given simply by ( 𝜋 a b)/4. 9

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Lab 2: Earth's Seasons D4. At an elevation angle of 45°, what is the major axis of the illuminated ellipse, in units of cm? (1 pt) D5. What is the minor axis of the illuminated ellipse (in cm)? (1 pt) D6. What is the area of the illuminated ellipse (in cm 2 )? (1 pt) So, why are we making you measure these areas? The ﬂashlight only has so much power, and the black tube restricts the light coming from the ﬂashlight into a cylinder. Thus, there is only a certain amount of light allowed to come out and hit the ground. Let's say there are "one hundred units of light" emitted by the ﬂashlight. Now let's convert this to how many units of light hit each square centimeter at angles of 90° and 45°. D7. At 90°, the amount of light per centimeter is 100 divided by the Area of the circle = ________________________ units of light per cm 2 . (1 pt) D8. At 45°, the amount of light per centimeter is 100 divided by the Area of the ellipse = _______________________ units of light per cm 2 . (1 pt) D9. Since light is a form of energy, at which elevation angle is there more energy per square centimeter? Since the Sun is our source of light, what happens when the Sun is higher in the sky? Is its energy more concentrated or less concentrated? (2 pts) 10

Lab 2: Earth's Seasons D10. Return the ﬂashlight/stand to the ground, and center/point the ﬂashlight at your globe (any orientation of the globe is fine). Use your (or a teammate's) finger to point to the location on the globe where the light is most intense, and take a photo. Embed it below, and explain what your photograph is showing in words. (2 pts) PART E - SUMMARY Let’s take what we have learned and push it to the extremes. Looking at the picture below, consider "sideways Earth"—if the Earth's axis was tilted at 90 degrees from its orbit. Also consider "upright Earth", where there is no tilt to the Earth's axis. 11

Lab 2: Earth's Seasons E1. Look at the diagram on the previous page and answer the following questions: a. Which of these three versions of Earth would show seasons? Select all that apply. (1 pt) Our Earth Sideways Earth Upright Earth b. Which Earth would have the strongest seasonal variation? (1 pt) Our Earth Sideways Earth Upright Earth c. Explain your reasoning for both. (2 pts) 12

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