CHARLESTON SOUTHERN UNIVERSITY PHYSICS 115 ASTRONOMY-STARS AND GALAXIES Student Name: …………………………………………… Date: …..... Student ID: …………………………………………… LAB 1: INTRODUCTION TO STELLARIUM Objectives • • Become familiar with the Stellarium program and its user interface Define and distinguish between systems of astronomical coordinates Introduction: In this activity, you will become familiar with the basic workings of the Stellarium program and you will be introduced to many of the procedures you will be asked to follow for other lab assignments in the course. Be sure to answer all of the questions. Installing the program: To run the program at home, you will need to install the program to your hard drive. Please access the website https://stellarium.org/ to obtain the free software. Stellarium also has a user guide available. Install the appropriate version for your operating system. When you click the version to install, the download should begin automatically after the next page loads. Windows users: Newer computers have 64-bit processors, but you can check using instructions found online. http://windows.microsoft.com/en-us/windows/32-bit-and-64-bit-windows#1TC=windows-7. To take the software out of full-screen mode, click the button shown to the right or click F11. (You may have 1 to hold Fn.) Fig 1. Start up the program. Once the main window pops up, you should be acquainted with the layout of the main interface. At the bottom is the status bar. On the far left, your location and altitude above sea level will be listed; the default setting is "Earth, Paris, and 38m." Next, it tells you the "FOV," i.e. your field of view from top to bottom. The default is 60˚. The following item displays the refresh rate for the animation in frames per second, or FPS. This will vary depending on the active memory being used by your computer. Finally, the date and time are displayed in the format "YYYY-MM-DD HH:MM:SS" in 24-hour time. For example, 2022 January 19 at 4:00 PM would be 2022 01-19 16:00:00. Daylight Saving Time is automatically run based on your location. Since this software is displaying what your local time would be, it is very important that you calibrate this. For the purposes of this assignment, make sure your computer's time zone is set to Eastern Time (UTC -04:00 during DST, UTC -05:00 in the winter months). There are dock menus, which pop out from the left side and the bottom. The left menu controls the broader settings, while the bottom menu controls your viewing settings. Place your mouse cursor over each of the buttons to get a description of what each button does. A keyboard shortcut will also be listed in brackets. Change your location from the default location in Paris. Access the Location window using either the shortcut key "F6" (you may have to hold the Function ["Fn"] key at the same time) or by clicking the top button on the left menu shaped like a compass. The search bar is to the right of the magnifying glass symbol, where you may type in the name of any town currently listed. Please find "North Charleston, SC, United States" in the list of cities and click on the name in the list. Make sure the coordinates match the following: Latitude: N 32o 51’ 16.56” Longitude: W 79o 58” 29.28” Altitude 0m. 2 Check the box on the lower left labeled "Use as default." Close the Location window by clicking the "☓" in the upper right-hand corner. You can change your view of the sky by dragging it with your mouse. Click and hold the mouse button on any point, which will allow you to change your view. You may also use the arrows on your keyboard to alter your viewable sky. When you select an object in Stellarium, the information for the object appears in the upper left corner of the screen, but the default setting displays more information than you may need. Either open the Configuration window using the shortcut key "F2" or by clicking the fifth button on the left menu shaped like a wrench. Select the Information tab. Uncheck the boxes for the following "Displayed fields:" Right ascension/Declination (J2000), Galactic coordinates, Hour angle/Declination, Ecliptic coordinates, and Additional Information. Select the Main tab, then click "Save settings," and close the Configuration window. The date and time can be adjusted either by accessing the “Date and Time” window using the shortcut key "F5" or by clicking the second button on the left menu shaped like a clock. You may change any entry by using the up and down arrow keys. If an entry is highlighted, you may also type in a new value. Practice changing the date and time to get comfortable using this feature. Change the date and time to 2020-10-08 at 12:00:00 (noon). If you don't see the Sun due South-East, i.e. directly above the “SE” in the sky, the clock on your operating system (Windows, Mac OS X) is not set to the Eastern Time Zone. When you are in the main window in Stellarium, typing the number "8" is a useful keyboard shortcut for setting the time. Set the date to 2020-01-01 at midnight, then type "8" in the main window. 1. How does typing "8" change the date and time? ------------------------------------------------------------------------------------------------------------------------- 3 Set the time to 21:00 (9:00 PM) before you move on to the next step. When viewing the sky, you will notice the ground and the sky, as well as the letter "S" at the horizon representing one of the cardinal directions, south. Keep an eye on the stars as the time changes. When using Stellarium, the sky normally moves in real time, but you can control this rate of motion. You have four buttons on the right side of the bottom menu, which control the rate of motion: Reverse, Play, Now, and Forward. Clicking the Reverse or Forward buttons multiple times allows you to speed up the time flow in either direction, and they can slow down the time flow when they oppose the motion. The Play button resets the time flow to real time and acts as a Pause button when the sky is changing in real time. Finally, the Now button changes the time flow to real time AND changes the date and time to the present. The Reverse, Play, and Forward buttons all have easy keyboard shortcuts as well: "J", "K", and "L". 2. From the real-time or Play setting, increase the Forward rate three times. Watch the southern sky for about 30 seconds and describe what you see. Which direction are the stars moving? -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Instead of altering the rate of time flow, you can move in discrete time steps. Pause the time flow and reset the time to 21:00 (9 PM). Pay attention to the time and date as you click the "-" and "=" keys. You can also change the time at different rates by holding down the "Ctrl" key at the same time. Mac users: For the keyboard shortcuts listed below, use Command (⌘) instead of Control ("Ctrl"). 4 3. Record how the date and time changes when using each of the following keyboard shortcuts: a) – b) = c) [ d) ] e) Ctrl – f) Ctrl = While looking at the sky as you would see it from North Charleston, you can select any of the points of light in your field of view to see some information about the object. Choose a bright, unlabeled point of light in the sky and click the mouse button to select it. 4. Write down the name of the object (only the first part listed), its magnitude (only the first number listed), and its distance from Earth rounded to one decimal place. Do not forget the distance units. Something that you will have noticed is that it is often hard to keep track of the stars because the Sun comes up. Fortunately, Stellarium allows you to remove the effects of daylight hitting the atmosphere. On the bottom menu, one of the highlighted icons looks like a cloud obscuring light. Clicking this button or typing the shortcut, "A", removes the atmosphere and allows you to see the stars hidden by scattered sunlight. 5 Celestial Coordinates: Fig. 2 Celestial coordinates allow us to communicate the location of objects in the sky. We will use four of these today and throughout the course. Azimuth (Az) is a coordinate, which measures the cardinal direction in the sky. North lies at an azimuth of 0˚, the numbers increase clockwise, going toward 90˚ in the east, 180˚ in the south, 270˚ in the west, and approaching 360˚ at it returns to north. Altitude (Alt) measures the angle relative to the horizon. The horizon has an altitude of 0˚ and the zenith, the point directly overhead, is 90˚ from the horizon. Objects below the horizon have negative altitudes. When the atmosphere is activated, the Az/Alt will be the (apparent) values, 6 which show how their positions are bent by the atmosphere. Turn your gaze to the north, i.e. drag the screen until the cardinal direction "N" is at the center of the horizon. Reset the time to 21:00 again. 5. Find the brightest star directly above the "N". When you select the star, its altitude should be about 40˚. Write down the star's name. From the real-time or Play setting, increase the Forward rate four times. With the star from question 5 near the center of the screen, watch how the stars move. 6. Describe how the star in question 5 moves. Describe how the other stars move. Once you are done, return to real time by pressing the Play button or the shortcut "K". Change your view direction so you are facing to the south and the letter "S" on the horizon is near the bottom of the screen. Change the date and time to 2021 May 4 (2021-05-04) and 22:00:00, respectively. This will be the time used for the rest of the lab. Make sure the time is paused. You should see a field of stars, the Moon almost directly south, and at least one labeled planet. If the moon is not visible, type MOON on the search window and enter. If you like, you may remove the labels for the planets, the Sun, and the Moon by clicking the planet-shaped icon on the bottom menu or by typing the shortcut, "P". 7. Identify the planet in the field of view closest to the Moon. Using "up, down, left, and right", where it is located relative to the Moon? 7 Of course, the planet does not look very exciting right now. Stellarium allows you to correct this by getting closer views of objects in the sky. After selecting the planet with the mouse, you may zoom in close to the planet by using the shortcut "/". To zoom out, you may use the shortcut "\". You may also use the Page Up and Page Down keys (Fn+Up on a Mac). 8. After magnifying the planet, list the size of the field of view (FOV) and describe the planet as you see it. 9. You should also see several of the planet's moons. If not, press "\" once. Name these moons and describe their layout relative to the planet. Please return the field of view to 60˚ and facing due south using your preferred method. Now we can look at ways in which you can navigate around the night sky. One way is to use celestial coordinates. Right ascension (RA) and declination (Dec) are coordinates in the sky which also measure east and west or north and south for RA and Dec respectively. Unlike azimuth and altitude, which make their measurements relative to the horizon, RA and Dec are measured relative to points in the sky. A declination of 0˚ is on a line called the Celestial Equator (like Earth's equator). The declination increases to 90˚ toward the North Celestial Pole and decreases to -90˚ approaching the South 8 Celestial Pole. The right ascension n is measured relative to a point in the constellation Pisces and is expressed in hours rather than degrees. Since it takes 24 hours for the stars to make a trip around the sky, RA ranges from 0 to 24 hours. Stellarium also shows the coordinates of the stars on the date currently displayed as RA/Dec (of date), e.g. J2020.4 for 2020-05-24. It can also show what the coordinates were in 2000 as RA/Dec (J2000). The numbers are slightly different because of precession. Rounding and degrees: Three of these coordinates are measured in degrees (°), arcminutes ('), and arc seconds ("). For example, you may see a declination of 19°35'12". Round them to the nearest degree by checking the arcminute value. If it is 30' or more, round up. In our example, it rounds up to 20°. The right ascension is listed in hours (h), minutes (m), and seconds (s). For example, you may see a RA of 7h20m39s. Round them to the nearest minute by checking the second value. If it is 30s or more, round up. In our example, it rounds up to 7h21m. 10. (a) While the planet is selected, record its azimuth and altitude rounded to the nearest degree. (b) Record the right ascension rounded to the nearest minute and declination rounded to the nearest degree. 11. (a) Now select the Moon and record its azimuth and altitude rounded to the nearest degree. (b) Record the right ascension rounded to the nearest minute and declination rounded to the nearest degree. 9 As you have already seen, in order to move from the position of the Moon to the position of the planet, you need to move westward and upward in the sky. Since each position in the sky has different coordinates, moving from the Moon to the planet has changed the "Az/Alt" and "RA/Dec" coordinates. 12. Compare your answers to questions 10 and 11 and the positions of the planet and the Moon. (a)Describe how both the altitude and the declination change for objects lower in the sky. (b)Describe how both the azimuth and the right ascension change for objects farther east (left) in the sky. In reality, astronomers only use coordinates if they are making detailed observations of objects located very far away. Amateur astronomers find their way around the sky by using familiar points of reference, such as bright stars. To make navigation easier, the sky was broken up into a set of 88 regions called constellations. You can display the constellations by clicking the buttons on the left side of the bottom menu. The far left button connects the brightest stars of the constellation, which can be activated with the shortcut "C". The second button, or the shortcut "V", displays the names of each constellation in the sky. Unfortunately, the lines and labels do not show you where each constellation begins and ends. The shortcut "B" will display the boundaries between each constellation. 13. Describe what has happened to the view on the screen when you display the boundaries. In what constellation is the planet from question 7 located? 10 If you have ever wanted to help learn where the constellations are in the sky, Stellarium can be very useful. The constellation lines may help you recognize the patterns of the brighter stars in the sky. By selecting the third button on the bottom menu or the shortcut "R", you can also see illustrations of each constellation. As a last task, let us find some objects in the sky. The easiest way to do this is to open the search window by clicking on the magnifying glass-shaped icon on the left side of the screen. Of course, you may also type "F3". As you type the name of an object like Jupiter, several objects will be listed below the search bar. Make sure you have Jupiter in boldface by typing "Tab", or you may go to the asteroid Juno instead. If the object is below the horizon, you may remove the ground by typing the shortcut "G" or finding the button shaped like a couple trees on the bottom menu. Make sure you have the same date and time set as before question 7. 14. Record the constellation in which the following objects are located: a) Mercury b) The Sun c) The Moon d) Vesta 11
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