Questions and Answers > Arizona State University AST 113 ASTRONOMY Lab 2

Arizona State University AST 113 ASTRONOMY Lab 2 Question 1 1 out of 1 points Rotational Motion of Earth We will start this lab by looking at the rotational motion of Earth. You will see the effect of rotationa ...

Arizona State University AST 113 ASTRONOMY Lab 2 Question 1 1 out of 1 points Rotational Motion of Earth We will start this lab by looking at the rotational motion of Earth. You will see the effect of rotational motion on the Northern Hemisphere, at the equator, at the North Pole, and in the Southern Hemisphere. You will then calculate the rising and setting angles for each of those locations. In this part of the lab, you will use the Starry Night software to learn about and answer questions related to the rotational motion of Earth. You should have a general familiarity with Starry Night before attempting this portion of the lab. To become more familiar with Starry Night, access the tutorial exercise within the software. Lab 2 Figure 1 - Click Image to Enlarge Rotational Motion of Earth: The Northern Hemisphere For this activity, make sure your viewing location is set to Phoenix, United States. To change your location to Phoenix, click on Viewing Location box and from the dropdown menu that appears selectViewing Locations -> Other.... In the popup menu that appears make sure the top selection has View from: Surface of Earth. Then Select the radio button titled Show Where then search for Phoenix, United States in the text box. When you have Phoenix selected, click Go To Location. Hit the spacebar key to skip the animation. Click the drop-down menu to the right of the Time and Date field (on the control panel at the top of your screen just above the viewing pane) and select Sunset. To turn on the Constellations go to the tabs of the left side of the Starry Night window and click on the View tab. Under the subject heading Constellations check the boxes for Boundaries, Labels, and Stick Figures. (At least I prefer the stick figures, you can select the illustrations if you desire.) Click the W viewing direction button on the button bar, or press W on your keyboard to look toward the west. Select 300× from the Time Flow Rate drop-down list. Click the PLAY button to have time move forward; keep this setting throughout this activity. Watch the stars and constellations set and note the direction in which they set. If, during this activity, you return to daylight, simply right-click the screen and select Hide Daylight to turn daylight off. If time should stop during the activity, click the PLAY time mode button to start again. Now switch your field of view toward the east by clicking the E viewing direction button or by pressing the E on your keyboard. Be sure that time is moving forward at 300×. Now that you are looking toward the east, note the angle in which the stars and constellations move. Now click the S viewing direction button on the button bar or press the S key on your keyboard to look toward the south. Be sure that time is moving forward at 300×. Note the direction in which the stars and constellations are moving this time. Be sure to look at the motion right above the south direction and for only short distances. Finally, look north by clicking the N viewing direction button on the button bar or by pressing the N key on your keyboard to look north. Note the motion you see here. To help you visualize the motion, click the Equatorial (Eq) coordinate system button to superimpose an equatorial coordinate system on the celestial sphere. To turn on the Equatorial coordinate system go to the tabs of the left side of the Starry Night window and click on the Options Tab. Under the subject heading Guides expand the arrow labeled Celestial Guides, Poles. This is the Equatorial coordinate system. Check the boxes for Equator, Grids, and Poles. The equator that you see projected on the sky extends from Earth's Equator. The lines you see are similar to lines of latitude and longitude on the Earth, but projected out to the sky. Continue moving forward in time at 300× and note the motion you observe. Lab 2 Figure 2 - Click Image to Enlarge The Earth is a sphere rotating in space. The motions of stars and constellations you have been observing are caused by Earth’s motion. The stars and constellations themselves are not moving to cause the apparent motion you observe. The discrepancies in motion demonstrated by your different viewing angles are a result of Earth’s spherical shape and rotational motion. Our view toward the north clearly shows how the stars appear to move about a specific point—that point being the projection of Earth’s North Pole out into space. We call this point the North Celestial Pole (NCP). The constellations revolving close to this point are referred to as circumpolar constellations. For higher latitudes, these constellations may never set; they simply go round and round the North Celestial Pole. Be sure to keep the Equatorial (Eq) coordinate system This is under Celestial Guilds in the Options tab our version of Starry Night, on as you work through these activities. Use your mouse to point at the star nearest to the North Celestial Pole. Information about this star should appear on your screen. Zoom in a bit by using the zoom control in the upper-right area of the control panel. Determine the angular separation of this star from the North Celestial Pole. You can do this by hovering the mouse directly over the star (watch as the hand turns to an arrow); while clicking and holding the mouse button, drag the mouse over to the North Celestial Pole. Your angular separation value will be given in degrees, minutes, and seconds of arc. Recall that there are 360 degrees in a circle, 60 minutes of arc in a degree, and 60 seconds of arc in a minute. The star you selected so close to the North Celestial Pole is almost directly aligned with the direction north on Earth; thus, we call this star the North Star (note the directions shown on the horizon). The North Star is not exactly aligned with the North Celestial Pole; however, it is within a degree of it. Also note that the North Star is not the brightest star in the sky. This is a common misconception. This star is not important because of its brightness, but rather because of its location. Being so close to the North Celestial Pole, it essentially doesn't move across the sky as other stars do, but remains fixed in the sky toward the north for all observers on Earth at all times of the year. For this reason, it is an important navigational aid and has guided many a traveler in many a culture over the ages. You hover over any star with the mouse, including the North Star, to find out more information; this information shows up as yellow text in the Sky Viewing window. To best appreciate this property of the North Star, select a time speed of 3000×. Note that the position of the North Star essentially does not vary, while the rest of the sky whizzes by. To Find the angular separation between two points on the sky, you can use the angular separation tool. This tool is found by clicking a button in the upper left of the Starry Night window (usually it has a hand symbol). After clicking on this button a drop-down menu appear with several cursor tools. The default selection is Adaptive but we want to select Angular Separation. To measure the angular separation using this tool, click and hold on the first point in the sky then drag to the second point while holding. The angular separation is reported in bold red under the cursor. After you are done using the angular separation tool you may want to put the cursor back to the Adaptive tool. After you have had a chance to explore, use the Starry Night software to answer these questions. When facing west, in which direction do the stars and constellations set? · Question 2 1 out of 1 points When facing east, in which direction do the stars and constellations rise? · Question 3 1 out of 1 points Are the rising and setting angles of stars the same? · Question 4 1 out of 1 points When facing south, in which direction do the stars and constellations seem to move? · Question 5 1 out of 1 points When facing north, which of the following best describes the motion of the stars and constellations? · Question 6 1 out of 1 points What type of star is the North Star? · Question 7 1 out of 1 points Polaris is the brightest star in the sky. · Question 8 1 out of 1 points What is the distance from the North Star to the Sun? · Question 9 1 out of 1 points What is the angular separation from the North Star to the North Celestial Pole (set the zoom to 58°x 32°)? · Question 10 1 out of 1 points Lab 2 Figure 3 - Click Image to Enlagre Rotational Motion of Earth: The Equator, North Pole, and Southern Hemisphere Let’s investigate the rotational motion of Earth further by traveling to other locations. First, let’s travel to the equator by selecting the Options menu and choosing Viewing Location. Select the Latitude/Longitude tab and enter 0 (zero N) as the latitude. Watch as you fly to your new location on Earth’s equator. Watch the motion of stars rising and setting from the west, east, south, and north, just like you did in the first section of this lab when your location was the Northern Hemisphere. Note the North Star’s motion while you’re at the equator. Next let’s travel to Earth’s North Pole. To travel to the North Pole, select the Options menu and choose Viewing Location; then select the Latitude/Longitude tab and enter 90 N for your latitude. Watch as you fly to the North Pole. Watch the motion of stars rising and setting from the west, east, south, and north. Now use the 'Z' directional button (located next to the NSEW direction buttons) to look straight up at the zenith. Which direction are the stars moving? Note the North Star’s motion while you’re at the North Pole. Finally, let’s travel to Earth’s Southern Hemisphere. How will Earth’s rotation cause things to look different to us in the Southern Hemisphere? To travel to the Southern Hemisphere, select the Optionstab and choose Viewing Location; select the Latitude/Longitude tab and enter 45 S for your latitude. Watch as you fly to the Southern Hemisphere. Watch the motion of stars rising and setting from the west, east, south, and north, just like you did when your location was the Northern Hemisphere. Note the stars’ motion while you’re in the Southern Hemisphere. Why do the motions appear as they do? What’s different compared to the motions we see from mid-latitude locations in the Northern Hemisphere? After you have had a chance to explore, use the Starry Night software to answer these questions. Facing west at the equator, in which direction are the stars moving? · Question 11 1 out of 1 points Facing south at the equator, in which direction are the stars moving? · Question 12 1 out of 1 points Looking straight up at the zenith while at the North Pole, in which direction are the stars moving? · Question 13 1 out of 1 points Facing south at the North Pole, in which direction are the stars moving? (Hint: it may be useful to shift your point of view upward from the horizon, to see what the stars are doing at the zenith.) · Question 14 1 out of 1 points Facing west in the Southern Hemisphere, in which direction are the stars moving? · Question 15 1 out of 1 points Facing north in the Southern Hemisphere, in which direction are the stars moving? · Question 16 1 out of 1 points Which of the following statements provides the best explanation for why the daily motion of stars appears differently from different locations on the Earth? · Question 17 1 out of 1 points Rotational Motion of Earth: Calculating Rising and Setting Angles For this section of the lab, set the Starry Night software to return to the Phoenix, United States location. Estimate the rising and setting angles you observed earlier by clicking both the Localcoordinate system button and the Equatorial coordinate system button, located at the top right of the button bar. As you move time forward at 300×, try to determine the angle of motion measured with respect to the horizontal as best you can. Determine the latitudes and rising angles at the Phoenix location, at the equator, and at the North Pole; note the comparisons. For this section of the lab, it might be helpful to record your measurements in a table to use to answer the questions. The latitude values can be found by clicking the Location button on the button bar and then selecting the Latitude/Longitude tab. The rising angle refers to the estimated rising angle as measured from the horizontal. You might have to use a protractor if you have one: Hold it to the screen as the motion is turned on and while the local and equatorial coordinate systems are showing. The setting angle (looking toward the west) should be the same, but just a mirror image of the rising angle. Be sure to record the angle in degrees. After you have found and recorded the latitudes and rising angles for all three locations, add the latitude and rising angle values together to get the Sum. Do you notice a pattern in your data? [OPTIONAL]To get more accurate values for the rising angles, do the following: Select the Angular Separation tool by clicking the Tool Selection icon at the far left of the control panel (by default, this button appears as a hand with a plus sign in it). While looking toward the west, click and hold on any spot on the local meridian line directly over the west direction (directly over the W on the horizon). You can turn on the meridian and its grid under the Options tab -> Guilds -> Alt Az Guilds -> check the boxes for Grid and Meridian. Hold and drag the pointer up along the meridian line. Continue to hold down the mouse button and note that two numbers are displayed. The first is the angular separation. The second is the direction as measured from the North Celestial Pole (the red lines of the equatorial coordinate system all lead to the North Celestial Pole). This procedure, if done properly, can yield an accurate rising angle (the second number). After you have had a chance to explore, use the Starry Night software to answer these questions. What is the rising angle for Phoenix? | · Question 18 What is the rising angle for the equator? | | | | | | · Question 19 What is the rising angle for the North Pole? | | | | · Question 20 1 out of 1 points What does the SUM come out to be for all locations on Earth? · Question 21 1 out of 1 points Thinking of the Earth as a rotating sphere, which of the following statements provides the best explanation for your answer to question 4? · Question 22 1 out of 1 points Lab 2 Figure 4 Lab 2 Figure 5 Seasonal Stars This next section of the lab is about seasonal stars. We will use the heliocentric model to explain why different zodiacal constellations appear in the night sky as the year progresses. Figure 4 shows a Sun-centered, or heliocentric, perspective of the Earth–Sun system. The figure shows the direction of both the daily rotation of Earth about its own axis and its annual orbit about the Sun. You are the observer shown in Figure 4, located on Earth in the Northern Hemisphere while facing south. Figure 5 shows a horizon view of what you would see when facing south on this night at the same time as shown in Figure 4. Which labeled constellation do you see highest in the southern sky? · Question 23 1 out of 1 points For the time shown, which constellation is just to the east (to your left when you are facing south), and which constellation is just to the west (to your right when you are facing south) of the highest constellation at this instant? · Question 24 1 out of 1 points Noting that you are exactly on the opposite side of Earth from the Sun, what time is it? · Question 25 1 out of 1 points In six hours, the observer will be able to see the sun. Selected · Question 26 1 out of 1 points In six hours, which constellation will be behind the sun? · Question 27 1 out of 1 points When it is noon for the observer, which constellation will be behind the sun? · Question 28 1 out of 1 points 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? · Question 29 1 out of 1 points Which direction do you have to look from the highest constellation that you see now to see the constellation that was highest one month ago at midnight? · Question 30 1 out of 1 points Does the constellation that was highest in the sky at midnight a month ago now rise earlier or later than it rose last month? Why? · Question 31 1 out of 1 points Lab 2 Figure 6 Solar Versus Sidereal Day The final part of this lab explores the difference between a solar day and a sidereal day. A solar day is defined as the time it takes for the Sun to go from its highest point in the sky on one day to its highest point in the sky on the next day; we divide that time into 24 hours. A sidereal day is defined as the time it takes for Earth to rotate exactly 360° about its axis with respect to the distant stars. Figure 6 shows a top-down view of the Earth–Sun system. Arrows indicate the directions of the rotational and orbital motions of Earth. For the observer shown, the Sun is highest in the sky at noon. Earth orbits the Sun in a counterclockwise direction once every 365 days. Approximately how many degrees does Earth move along its orbit in one day? · Question 32 1 out of 1 points As Earth orbits the Sun, it also rotates in a counterclockwise direction about its axis as shown in Figure 6. We define 24 hours as the time from when the Sun is highest in the sky one day to when it is highest in the sky the next day. How many degrees does Earth rotate about its axis in exactly 24 hours? · Question 33 1 out of 1 points How long does it take Earth to rotate exactly 360°? · Question 34 1 out of 1 points Earth rotates about its axis once every 24 hours; one rotation equals 360°. · Question 35 1 out of 1 points Earth rotates a greater amount during a sidereal day versus a solar day. · Question 36 1 out of 1 points A sidereal day takes a shorter amount of time than a solar day.