A02_Celestial Motion

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Old Dominion University Physics 103N Laboratory Manual 1 OLD DOMINION UNIVERSITY PHYS 103N A02 – CELESTIAL MOTION Submitted By: 1. Pyrox Rabach 2. Janine Bruendermann 3. Bhaavan Goswami Submitted on Date 25 January 2024 Lab Instructor

2 Experiment A02: Celestial Motion Celestial Motion Experiment A02 Objective ● To review various astronomical topics: Celestial Motion, Constellations, Causes for the Seasons, and the Lunar Cycle Materials Computer with Internet Access Procedure During this lab we will use simulations that have been created at the University of Nebraska-Lincoln. These simulations will let us test a few astronomical concepts that are difficult to replicate in the lab. The simulations let us test and adjust things much more easily than we can in the real world. These simulations use a combination of Java & Flash and are readily available for free. Start by downloading the install files from Canvas, or, if you are on your own computer, visiting the website https://astro.unl.edu/nativeapps/ On this site, there are two categories of files: Windows and MacOS. You will need to download the NAAP Labs file and the Classaction file that is the appropriate file type for your computer. Once you have the files downloaded, go to the folder where they are saved on your computer. Double click one of them to install the simulations. Once the first program is installed, then install the other. The file sizes are small (~22 MB and ~97MB) and should install quickly. After the installations have finished, you will have a program on your computer titled NAAP Labs and one called Classaction . In today’s experiment, we will only use the NAAP Labs. Open this program and a window like the one to the right will open. The first simulation we are using is located under 3. The Rotating Sky . Click on this title and then click on Rotating Sky Explorer on the next page. This simulation has two views: the left view shows the celestial sphere and how the Earth spins within it, the right view is your view from the ground and how you see the celestial sphere move (similar to what you saw on the dome earlier in the lab). Take a few minutes to familiarize yourself Part A: Celestial Motion

Old Dominion University Physics 103N Laboratory Manual 3 with how the simulation works and then answer the questions below. (Hint: Things to try with the simulation are to change your location on the Earth, drag around the globe, add stars to the celestial sphere, and add star trails. Make sure you click the Start Animation button to see the simulation run.) 1. Why do all objects on the celestial sphere rise in the east and set in the west? (This answer requires much more detail than just, “Because the Earth rotates.”) Because the Earth’s rotation is counterclockwise(from the perspective of the Northern hemisphere), objects appear to move from east to west. 2. Set the location to Norfolk, (latitude = 36.9° N, longitude = 76.2° W). From this location:

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4 Experiment A02: Celestial Motion a. Are there stars that never rise? There are stars that never rise, because they never appear above our horizon and so can’t be seen from here. b. Are there stars that never set? There are stars that never set, because they never go below the horizon, such as the star Polaris. c. Are there stars that are always up? What is the name for this type of star? There are stars that are always up, which are called circumpolar stars. 3. From Norfolk, what direction do you have to look to see circumpolar stars? North 4. As you increase your latitude do you see more or less circumpolar stars? As you decrease your latitude do you see more or less circumpolar stars?

Old Dominion University Physics 103N Laboratory Manual 5 As you increase your latitude and get closer to the poles, you see more circumpolar stars, since you have less of an angle towards the poles. As you decrease your latitude, you will thus see fewer circumpolar stars. 5. What do you think the motion of the stars would look like if you were at the North Pole? Where would Polaris (the North Star) be located? The motion of the stars at the north pole would be that you would have the stars circling overhead, and all stars would be circumpolar. 6. What do you think the motion of the stars would look like if you were at the Equator? Where would Polaris be located? All stars would move horizontally across the sky, which means that there would be no circumpolar stars, since all stars would rise and set. Part B: Reasons for the Seasons

6 Experiment A02: Celestial Motion 1. Draw arrows in the diagram to indicate the direction the Earth travels around the Sun. 2. Label Northern spring, summer, fall, and winter. 3. Label Southern spring, summer, fall, and winter. 4. The distance between the Earth and Sun during 4 months of the year are listed in the chart to the right. Based on this data, what can you conclude about the effect that the Earth-Sun distance has on the seasons? Support your conclusion by citing specific data. The distance between the Sun and Earth does not materially affect the temperature on Earth. We can see that by December being the month where Earth is closest to the Sun, while December is one of the coldest months. Month Earth-Sun Distance March 149 million km June 152 million km September 150 million km December 147 million km

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Old Dominion University Physics 103N Laboratory Manual 7 5. Describe, in your own words, what causes the seasons. Specifically, why does the tilt of the Earth’s axis result in some warmer months and some cooler months? The tilt of Earth’s axis determines the seasons because of the amount of direct sunlight hitting the surface. Places facing the sun directly will receive more direct sunlight, which heats it more, while places facing away from the sun receive less, which means that they will be cooler. 6. If, somehow, the Earth’s tilt changed from 23.5° to just 5°, what would change about the seasons? If the tilt of the Earth changed to 5 degrees, the seasons would be a lot less pronounced, and there would be less temperature difference between them. The largest differences would be seen at the poles, and the equatorial region would get a very slight change. In the NAAP Labs program, click the NAAP Labs label in the top left to return to the main selection page. Our next simulation is located in 6 – Lunar Phases . On the next page, choose Lunar Phase Simulator . This simulation is a top-down view of the Earth looking at the North Pole. It can also show the Part C: The Lunar Cycle

8 Experiment A02: Celestial Motion position of the Moon in its orbit and the associated phase. Take a few minutes to familiarize yourself with how the simulation works, combine what you see in the simulation with the diagram below, and then answer the questions. 1. What Moon phase will an observer see if the Moon is directly overhead at sunset? A First Quarter Moon. 2. What Moon phase will an observer see if the Moon is directly overhead at sunrise? A Third Quarter Moon. 3. What Moon phase can be seen for half of the night and then half of the day? Third Quarter Moon 4. What Moon phase can be seen for half of the day and then half of the night? First Quarter Moon 5. The following sketches of the moon's appearance were made over about four weeks. Identify the phases and put them in the correct numerical order (full Moon is considered as 0, the starting point). One is labeled for you.

Old Dominion University Physics 103N Laboratory Manual 9 Picture Order Phase Picture Order Phase A 3 Waning Crescent D 4 First Quarter B 1 Waning Gibbous E 5 Waxing Gibbous C 0 Full Moon F 2 Waning Crescent 6. In the diagram below the sun's light is coming in from the right. The moon's location is marked at several points on its orbit. These are the points the moon was at when the sketches above were drawn. Identify each position with the letter of the corresponding sketch.

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10 Experiment A02: Celestial Motion 7. How long does it take the Moon to complete one cycle of phases, in days? It takes 29 days. 8. If the Moon is full today, what phase do you expect it to be at in a week? Third Quarter 9. How about one month later? Full Moon 10. Is there a dark side of the Moon? (Note: this question can be effectively answered either yes or no, so it is important to thoroughly explain your reasoning.) Yes, that’s the side of the moon that we never see, since the moon’s rotation means that we effectively never see part of the moon directly from Earth. An eclipse is an astronomical event that occurs when an object is temporarily obscured, either by passing into the shadow of another body or by having another body pass between it and the viewer. Part D: Eclipses

Old Dominion University Physics 103N Laboratory Manual 11 The term eclipse is most often used to describe either a solar eclipse, when the Moon's shadow crosses the Earth's surface, or a lunar eclipse, when the Moon moves into the Earth's shadow. However, it can also refer to such events beyond the Earth–Moon system: for example, a planet moving into the shadow cast by one of its moons, a moon passing into the shadow cast by its host planet, or a moon passing into the shadow of another moon. A binary star system can also produce eclipses if one star passes in front of the other. This portion of the lab will explore help you visualize the conditions needed for an eclipse to occur. We will start with the ClassAction software that we had mentioned in the previous experiment. If needed, you can downloaded it here: https://astro.unl.edu/nativeapps/ The program should also be available on the lab computers. Start by opening the ClassAction program and you will open to a page similar to the picture to the right. Click on Lunar Cycles and then the Animations button at the bottom. Finally, open the simulation Eclipse Shadow Simulator .

12 Experiment A02: Celestial Motion This simulation allows you to visualize systems like the Earth, Moon, and Sun and how their shadows interact with each other to cause eclipses. Keep in mind, this simulation is not to scale. Click and drag around the Earth (the blue object) and the Moon (the gray object) in order to see how their distance from the Sun changes the shape of their shadows. Position the Earth and Moon for a solar eclipse to occur and then for a lunar eclipse. 1. In the space below, draw the relative positions of the Sun, Earth, and Moon for both a solar eclipse and a lunar eclipse. Solar Eclipse Lunar Eclipse

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Old Dominion University Physics 103N Laboratory Manual 13 2. The angular size of an object is the angle it appears to span in your field of vision. This can be calculated with the following equation: 𝑎𝑛𝑔?𝑙𝑎? ?𝑖?? = 𝑝ℎ??𝑖?𝑎𝑙 ?𝑖??× 360° 2π×?𝑖??𝑎𝑛?? a. The Moon’s diameter is 3.48 x10 3 km and the distance between the Earth and the Moon is, on average, 3.84 x10 5 km. The Sun’s diameter is 1.39 x10 6 km and the distance between the Earth and Sun is, on average, 1.50 x10 8 km. Calculate the angular size of the Moon and the angular size of the Sun from the point of view of an observer on Earth. The Moon’s angular size is 0.52 degrees. The sun’s angular size is 0.57 degrees. b. Based on your answers above, if the Moon’s physical diameter is much smaller than the Sun’s physical diameter, how is it that the Moon can block the entirety of the Sun during a total solar eclipse? Because it’s closer, the moon appears larger in the sky relative to its sky, and thus it can block the sun. c. To help with the previous question, consider the size and distance ratios of the Sun

14 Experiment A02: Celestial Motion compared to the Moon. Calculate the ratio of the size of the Sun compared to the Moon (Sun size/Moon size) and the distance ratio (Sun distance/Moon distance). What do you notice about these ratios? Are they the same? Similar? Different? Wildly different? The sun is roughly 400 times times wider than the moon, and it is 390 times further away. Thus, because these ratios are both similar, both appear roughly the same size in the sky, though the sun is roughly 10% larger in the sky. d. Why do annular solar eclipses sometimes occur instead of total solar eclipses? Annular solar eclipses happen when the Moon is at its farthest from Earth, so it doesn’t completely cover the Sun.

A02_Celestial Motion

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