Earth's Rotation: Observing Sky Movement and Star Patterns

Astronomy/Solar System Notes (from your tutor) Homework 2: Earth’s Rotation (Pearson Astronomy) As Earth spins on its axis, the Sun, Moon, stars and everything beyond Earth appears to move across the sky. When thinking about observing the sky from a spinning Earth, it is usually easiest to imagine a counter-clockwise spinning Earth as seen from above its North Pole. The Figure at right shows the Earth as seen from above the north pole. An observer on the equator experiences local noon. A, B, and C mark observer positions with different local times. D, E, and F mark the possible positions of objects in the sky. (a) Which observer position corresponds approximately to midnight B (b) Which observer position corresponds approximately to 6 am? C (c) Which observer position corresponds approximately to 6 pm? A (d) The bright star Rigel in the constellation of Orion is seen high in the sky at midnight. Which position (D, E, or F) is most consistent with this observation? E (e) If the Moon is high above an observer’s head at sunrise, which position (D, E, or F) is most consistent with this observation? D (f) Objects in the sky appear to rise and set because Earth spins on its axis. If a star rises in the East at 8:00 pm on a Monday night, how many hours must pass before it rises again? About 24 hours (g) If Earth is spinning twice as fast, only taking about 12 hours to spin once, how long would it take for a star to appear to move across the sky from the Eastern to the Western horizon? About 6 hours

(h) From the mid-latitudes of the Northern hemisphere, the seven stars of the Big Dipper never appear to rise and set, but to move around the North Star (Polaris) counter-clockwise. In the middle frame below, what should be the location of the Big Dipper with respect to Polaris? Above Polaris 1/26: Pre Class Questions Is there any location on Earth where an observer can see all 88 constellations in the course of one year ? No, there is not a single location on Earth where a person can see all 88 constellations in the course of one year. The visibility of a constellation depends on the latitude in which you are standing and also the tilt of the Earth’s axis. If you are near the equator, you can see a large portion of the celestial sphere over the course of a year, but not all 88 constellations due to the tilt of the Earth’s axis. Use your own words, explain the following terms: Celestial Sphere: it is an imaginary sphere surrounding the Earth. The stars, plants, and galaxies appear to be projected when viewed from Earth. It is a helpful tool in astronomy for visualizing the position of celestial bodies as they move across the sky with regards to the Earth’s rotation. Zenith: it is the highest point in the sky but is different for each observer depending on their location (longitude and latitude) on the Earth. Meridian: it is an imaginary line that runs through an observer’s zenith and connects the north and south poles. It also represents the highest point in the sky reached by the Sun, stars, and other celestial objects as they cross the observer’s line of sight. It cuts the sky into two halves. In the eastern half, the celestial objects rise and in the western half, the celestial objects set.

1/29: Pre Class Questions Do all stars rise and set every day? Explain Most stars do appear to rise and set every day. The stars rise up from the east horizon and set over the west horizon. Every 24 hours the stars that rise and set are above the horizon exactly half of the time. There will be times when the sun is too bright to see some of these stars. There are some stars that neither rise or set and they are called Circumpolar Stars. They are above the horizon every day of the year. When the sun is out and it’s daytime you can not see them, but they remain in the sky. They circle endlessly in what appears to be a counterclockwise pattern around the North Star. These constellations are visible in the northern night sky any night of the year. \ In North America, if a star rises due east at sunset, at what time will it be highest in the sky? In what direction should you face to see it? Explain If a star rises in the east at sunset in North America, it will be highest in the sky at approximately midnight. The star will move across the sky towards the west. When the star reaches its highest point this is known as its culmination point. In order to see it, a person will need to look toward the south. The reason you need to look toward the south is because of the Earth's rotation on its axis. Even though the star is moving east to west, it will also appear to move slightly south as a result of the Earth’s rotation. HOMEWORK 3: Position (a) Is the horizon shown a real physical horizon or an imaginary plane that extends from your observing location on Earth out to the stars? Imaginary. The horizon the observer sees is real, but the one shown denotes where the observer's line-of-sight along the real horizon intersects the celestial sphere.

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(b) Can the observer shown see a star when it is located below the horizon? No, only stars above the horizon can be seen by the observer (c) Is either Star A or B ever in an unobservable position? If so, which position(s)? Yes, star A is unobservable at position 4 when it is below the horizon. Star B is never below the horizon, so it is never in an unobservable position. (d) When a star travels from a position below the observer's horizon to a position above the observer's horizon, is that star rising or setting? The star is rising. (e) When a star travels from a position above the observer's horizon to a position below the observer's horizon, is that star rising or setting? The star is setting. (f) Star A is just visible above your eastern horizon at Position 1. At which of the numbered positions is it just visible above your western horizon? Position 3 (g) At which position, if any, does star B rise and set? Star B does not rise or set because it is circumpolar (h) two students are discussing their answers to Part G student 1: locations b1 and b3 are on my horizon because they are rising and setting just like a1 and a3. student 2: figure 1 shows that star b is as low as it will get when it is just above the northern horizon at b4. so star b never goes below the horizon. Do you agree or disagree with either or both of the students? Explain. Agree with student 2. Rising and setting are defined with respect to a horizon. A star's path must cross the horizon to rise and set. Star B never crosses the horizon, and in fact, is nearest the horizon only when it is due north. (i) Drag the direction labels into the correct boxes. (j) For each indicated position, match where in the sky you must look to see the star at that time. Each description has two pieces of information: the direction you must face and how far above the horizon you must look. A1: East Low A2: South High A3: West Low

A4: Cannot see STAR B4: North Low B1: Northeast High B2: Directly overhead: Zenith B3: Northwest Low (k) Does star B ever set? No, star B is circumpolar https://quizlet.com/463692681/astronomy-1504-lecture-tutorial-position-diagram/ 1/31: Pre Class Questions What is the SUMMER TRIANGLE? Which 3 stars does the summer triangle consist of? Indicate the source of your answer.

The Summer Triangle is made up of 3 of the brightest stars in the sky and is found in the northern celestial hemisphere The 3 stars are known as Vega, Altair, and Deneb. The triangle is at its brightest during late June through July and will appear toward the east but move overhead as the month of July passes. The triangle is not a constellation, but rather known as an asterism. An asterism is a noticeable pattern of stars. Each star of the Summer Triangle belongs to a different constellation. Vega is part of Lyra the Harp, Altair is part of Aquila the Eagle, and Deneb is part of Cygnus the Swan. https://earthsky.org/favorite-star-patterns/summer-triangle-asterism-vega-deneb-altair/ Which constellation does Regulus belong to? Explain how you found the answer and cite your source. Regulus belongs to the constellation Leo. It is one of the brightest stars in the entire sky. Regulus is often referred to as the “heart of the lion”. Regulus is at the bottom of an asterism commonly referred to as ‘The Sickle’. The sickle also looks like a backwards question mark. REgulus is visible during spring in the Northern Hemisphere. It will pass across the sky during March and April. During the month of May, it is seen in the eastern evening sky just after the sun sets and appears to have a blue-white color. An interesting fact about REgulus is it is actually 4 small stars, but to the naked eye it appears as one star. https://earthsky.org/brightest-stars/best-regulus-the-heart-of-the-lion/ Homework 4: Motion (Pearson Astronomy) (a) Note in Figure 1 that the position of Star B at 6 P.M. has been identified for you. Circle the numbered position (1, 2, 3, or 4) in Figure 2 that corresponds to the identified location of Star B at 6 P.M. provided in Figure 1. Position 3

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(b) The rotation of the celestial sphere carries Star B around so that it returns to the same position at about 6 p.m. the next evening. Label each of the X’s in both figures with the approximate time at which Star B will arrive (e.g. the location you circled in Part (a) will be labeled “6 p.m.”) 6 pm 12 am (midnight) 6 am 12pm (noon) (Appears to go counter-clockwise) (c) Match the times with the four marked positions in Figure 2. (celestial sphere) 6 pm 12 am (midnight) 6 am 12pm (noon) (Appear to go Clockwise) (d) Using Figure 2, describe the direction you have to look to see Star B at 6 a.m. Directly overhead (e) The position directly overhead is called the zenith. How does the direction of the zenith compare to the direction that you identified in (d) ? It is at the same spot (directly above) (f) In Figure 1, the dashed line shows the path followed by Star B. To indicate the star’s direction of motion along this path, drag and drop appropriate direction labels to each position marked with an “X”. Counter-clock wise (g) Using Figure 2, describe where you would look to see Star A when it is halfway between rising and setting. High South (h) Figure 3 shows an extended view along the eastern horizon showing the positions of Stars A and B at 6pm. The arrow shown is provided to indicate the direction that Star B will be moving at 6pm. Draw a straight arrow at the x in the east in Fig 3 to indicate the direction Star A moves as it rises. 45 degree angle going right

(i) Two students are discussing the direction of motion of a star rising directly in the east. Student 1: Stars move east to west so any star rising directly in the east must be moving straight up so that it can end up in the west. If the arrow were angled, the star would not set in the west. Student 2: I disagree. From Figure 2, the path of Star A starts in the east, then it moves high in the southern sky yet still sets in the west. To do this it has to move toward the south as it rises so I drew my arrow angled up and to the right. Which student do you agree with? Student 1: Disagree because moving straight up does not follow the path revolving around the North Star. Student 2: Agree because the path it follows moves high in the south before it sets in the west. (j) Imagine you could see Star B at noon. Fifteen minutes later, in what direction will Star B have moved? A bit lower in the northwest: Down toward the horizon (k) Consider the student comment below. Student: The amount of time that all stars are above the horizon is 12 hours because it takes 12 hours for a star to rise in the east and then set in the west. Do you agree or disagree with the student? Disagree because not all stars rise and set.

(l) Consider the situation below in which the Sun and a group of constellations are shown at sunrise. Figure 4, and then show again 8 hours later, Figure 5 Consider the following debate between two students regarding the motion of the Sun and constellations shown in Figures 4 and 5. Student 1: We know the Sun rises in the east and moves through the southern part of the sky and then sets in the west. Eight hours after sunrise, it makes sense that the Sun will have moved from being on the eastern horizon near the constellation Cancer to being located high in the southwestern sky near the constellation Aries. Student 2: You're forgetting that some stars and constellations also move from the east through the southern sky and to the west just like the Sun. So, the Sun will still be near Cancer eight hours later. So Figure 5 is drawn incorrectly. It should show that the constellations have all moved like the Sun, so Cancer would also be located high in the southwestern sky, with the Sun, eight hours later Do you agree or disagree with either or both of the students? Explain your reasoning. Check your answers with another group. Student 1: Disagree because he forgot that the stars also move. Student 2: Agree because since the Sun and constellations are both moving, the Sun rises with Cancer, therefore sets with Cancer as well. 2/2: Pre Class Questions What's the bright band in the sky called? What does it consist of? Explain. The bright spiraled band in the sky is called the Milky Way. It is composed of hundreds of billions of stars, including our sun. When you are standing in a very dark location, without light pollution, the band of stars appears to look like a milky colored cloud. We live within the galaxy of the Milky Way. The Milky Way is approximately 100,000 light-years across, or 600,000 trillion miles. In addition to the stars, there is dust and gasses that are bound together by gravity. You observed a star and measured that it is 5 fists away from (above) the horizon. Approximately what is the altitude of the star? Explain. The approximate distance of a star that I measured to be ‘5 fists above the horizon’ would be about 50 degrees above the horizon. You use the ‘fist method’ to measure. Each width of the fist would measure approximately 10 degrees.

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2/5: Pre-Class Questions What is the ecliptic? Why does the ecliptic and the celestial equator intercept at an angle of 23.5º? The ecliptic is the projection of the Earth’s orbit onto the celestial sphere. It is the apparent path that the Sun traces across the sky over the course of a year as seen from Earth. The ecliptic is significant because it’s the path along which the Sun, Moon, and planets appear to move. The angle of 23.5 degrees is due to the tilt of Earth’s axis in relation to its orbit around the sun. This tilt causes the plane of the celestial equator, which is Earth’s equator projected onto the celestial sphere, to be inclined at an angle of 23.5 degrees to the plane of the ecliptic. (The ecliptic is the path of the sun in the sky).

How long does the Sun take to move from being next to a bright star, all the way around the celestial sphere, and back to that same bright star? Explain your reasoning. The time it takes for the Sun to appear next to a bright star and the return to the same position relative to that star is approximately one year or 365 days. This is because the Sun moves approximately 1 degree per day. Over the course of these 365 days, the Sun appears to move along the ecliptic, passing by different constellations and stars. Eventually, the Sun returns to its original position relative to a specific bright star when observed from Earth. HOMEWORK 5: Seasonal Stars

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(a) Which labeled constellation do you see highest in the southern sky? Taurus (b) For the time shown, which constellation is just to the east (i.e., to your left when you are facing south) of the highest constellation at this instant? Gemini (c) Which constellation is just to the west (i.e., to your right when you are facing south) of the highest constellation at this instant? Aries (d) Noting that you are exactly on the opposite side of Earth from the Sun, what time is it? Midnight (e) In six hours, the observer will be able to see the Sun. In what direction would the observer look to see the Sun? East (f) Which constellation will be behind the Sun at the time described in Part (e)? Gemini (g) When it is noon for the observer, which constellation will be behind the Sun? Leo (h) One month later, Earth will have moved one-twelfth of the way around the Sun. You are again facing south while observing at midnight. Which constellation will now be highest in the southern sky? Gemini (i) Do you have to look east or west of the highest constellation that you see now to see the constellation that was highest one month ago at midnight? West (j) Does the constellation that was highest in the sky at midnight a month ago now rise earlier or later than it rose last month? Earlier

Figure 3 shows the same Earth–Sun view as before and the bright star Betelgeuse, which is between Taurus and Gemini. (k) Imagine last night you saw the star Betelgeuse just starting to rise on your eastern horizon at 7:15 pm. At 7:15 pm. tonight, will Betelgeuse be? Above the Eastern horizon because it rises earlier each morning. So it has to be slightly higher than the day before. Two students are discussing their answers to Part (k). Student 1: Earth makes one complete rotation about its axis each day so Betelgeuse will rise at the same time every night. It will therefore be exactly on the eastern horizon. Student 2: No. Because Earth goes around the Sun, the constellation Taurus rises earlier each month and so it must rise a little bit earlier each night, too. Betelgeuse must do the same thing. Tonight it would rise a little before 7:15 and be above the eastern horizon by 7:15. (l) Do you agree or disagree with either or both of the students? Agree with STUDENT 2: because Betelgeuse is rising earlier the second night, so it must be higher by the time it is 7:15.

2/7: Pre-Class Questions

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In Bowling Green, on which day(s), if any, would the Sun not cast a shadow at noon? Please explain. There are NO days in Bowling Green where the sun does not cast a shadow. This phenomenon only happens between the Tropic of Cancer and the Tropic of Capricorn. Bowling Green is above the Tropic of Cancer so there will always be a shadow at noon. This is due to the Earth tilt that is similar to the tilt of the Tropic of Cancer and Tropic of Capricorn. In Bowling Green, on which day would the Sun cast the longest shadow at noon? Please explain. The longest shadow at noon in Bowling Green would occur during the winter solstice, which usually falls around December 21st. The shadow would be the longest at noon because that's when the sun is at its lowest point in the sky. This happens because the Earth’s axis is tilted away from the sun.

2/9: Pre-Class Questions The local noon is the time when the sun reaches its highest point in the sky. The sun will be on the meridian. Do you think the local noon is at 12 pm each day in Bowling Green? Why or why not? No, local noon is not always at 12pm in Bowling Green. Local noon can vary due to factors such as the tilt of the Earth’s axis and Earth’s elliptical orbit; the rotation of the Earth slowly shifts the meridian. This causes the local noon to be slightly more east or can also be slightly more west. It does occur around 12pm, but can be slightly before or slightly after. Local noon will also be when an object's shadow is the shortest. What day is it when the sun is in the northernmost location on the celestial sphere? Which direction should you be facing when you observe the sun at noon this day? Explain. The day when the sun is in the northernmost location on the celestial sphere is the summer solstice, which occurs on June 21st. Since the latitudes of the continental United States are lower than the Tropic of Cancer you would be facing south to see the sun. The sun will be on the meridian at about 73.5 degrees at its northernmost location on the celestial sphere. Homework 6: Path of the Sun (a) According to Figure 1, in which direction would you look to see the Sun when it reaches its highest position in the sky today? South (b) If it is wintertime right now (just after the winter solstice), how does the height of the Sun at noon change over the next several months? Increases, the arc gets higher (c) Since Figure 1 is a reasonable representation for observers in the continental United States, is there ever a time of year when the Sun is directly overhead at the zenith (looking straight up) at noon? If so, on what day does this occur? No, the sun is never directly overhead in the continental United States

(d) During which two days throughout the year would the Sun rise directly in the east? Select two answers. Fall Equinox and Spring Equinox (e) Does the Sun always set in precisely the same location throughout the year? No, It sets North of West in the summer months and South of West in the winter months. (f) Figure 2 shows a small, vertical stick, which casts a shadow while it rests on a large piece of paper or poster board. You can think of this to be somewhat like a sundial. For two different days of the year, the end of the shadow has been marked with an x every couple of hours throughout the day. Although this sketch is somewhat exaggerated, these shadow plots indicate how the position of the Sun changes in the sky through the course of these two days. The following questions are designed to show the relationship between Figure 1 on the previous page and Figure 2 above. What do the x's in the shadow plots represent? The end of each shadow at the time the X was drawn (or the pathway of the sun across the sky) (g) Approximately how much time went by from the time one of the x's was drawn until the next x was drawn for each shadow plot? 2 hours (h) Approximately how long did it take to create each of the shadow plots? 12 hours (i) How does the direction of the stick's shadow compare to the location of the Sun at the time each x was drawn? The sun's direction is opposite the end of the shadow stick. (j) Using Figures 1 and 2, in what direction would the shadow of the stick be cast on the poster board if the Sun rises in the southeast? Northwest

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(k) Compare the position of the x that corresponds to noon for Shadow Plots A and B. Which Shadow Plot (A or B) corresponds to a path of the Sun in which the Sun is highest in the sky at noon? Shadow Plot B (l) Which Shadow Plot (A or B) most closely corresponds to the Sun's path through the sky during the summer? Shadow Plot B (m) Based on the shadow plots in Figure 2, during which time of the year does the Sun rise to the south of east? Winter (n) If Shadow Plot A corresponds to the path of the Sun on the day of the winter solstice, is it possible that there would ever be a time when the stick would cast a shadow longer than the one shown along the north-to-south line that indicates the Sun's position at noon? No, because the winter solstice is the shortest day of the year and the sun is at its lowest, therefore casting the longest shadow. (o) If Shadow Plot B corresponds to the path of the Sun on the day of the summer solstice, is it possible that there would ever be a time when the stick would cast a shadow shorter than the one shown along the north-to-south line that indicates the Sun's position at noon? No, because the summer solstice marks the longest day of the year and the sun is at its highest, therefore casting the shortest shadow possible. (p) Will the stick ever cast a shadow along the north-to-south line that extends to the south of the stick at noon? NO (q) If the stick is located in the continental United States, are there any days of the year when the stick casts no shadow at noon (assuming clear weather)? NO, sun is never overhead in the continental United States 2/12: Pre-Class Questions What gas does the Earth orbiting satellites use to track the activities of the plants in different seasons? Why can this gas tell us about the activities of the plants? Carbon Dioxide is the gas that satellites use to track the activities in different seasons. Plants are photosynthesizers and depend on the sunlight so they respond to the changes of the seasons. The satellites measure the amount of carbon dioxide absorbed by the primary producers. The sunshine in the spring causes skyrocketing increases in productivity. The phytoplanktons in the bottom of the ocean initiate the beginning of the food web. All ocean life also responds to the changes in the seasons. Trees are dependent on their leaves in the spring when the sunlight is increasing through the same process of photosynthesis. The leaves draw in the carbon dioxide and water and turn it into sugars that

feed the tree. In the seasons with less hours of sunlight, the plants and trees become dormant as they are not receiving this food source and that is when we see Fall and eventually Winter season cycles. Which month is the Earth closest to the Sun? What season is this month usually in? Do you think the distance to the Sun is the reason why we have seasons?

Astronomy_ Test 1

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