Stellarium - Mapping The Sky copy

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Astronomy

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May 10, 2024

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Name: Nina Mundy_____________________________ Date: 2/26/2024______________________________ Mapping the Sky ( Stellarium Exercise #4) Ever tried to give someone directions to a friend's house without knowing the exact address? It’s hard! Just as buildings have addresses to help us find them, astronomers need ways to locate things in the sky. Ideally, there should be a precise way to map the sky, just as we have a map of the surface of the Earth. To locate any point on the surface of the Earth, we specify the point’s LATITUDE and LONGITUDE , two angles that measure a spot's position relative to the center of the Earth. For example, Los Angeles (at least the center of it) is located at 34º North , and 118º West . Similarly, we need a way to tell other astronomers where to look for things in the sky. We can’t just say “Look to the left of that bright red star and then go up a little.” In this assignment, we’ll study the two ways of locating objects in the sky using angles – one called Altitude & Azimuth (Alt/Az) , and the other called Right Ascension & Declination (RA/Dec) - and their relative advantages & disadvantages. PART A Start Stellarium . Make sure your location is Los Angeles . If it is not, open the Location window, enter Los Angeles in the search box and then click on Los Angeles, United States , and then close the Location Window. Turn off the Atmosphere and Fog (if they're on), by pressing the A and F keys. Put the horizon at the center of the screen by dragging it until it's at the center. It doesn't matter which part of the horizon – N, S, E or W, you choose. Pick a bright star that is as close to the horizon as possible. Click on it. Information on your star will appear in the upper left-hand corner of the screen. • What is the common name of your star? Gru__________________________________ In the information, look for the line that starts Az/Alt . Az/Alt stands for Azimuth/Altitude , and the numbers on this line list the angles that are the star's Azimuth and Altitude, as discussed in class. The first number listed is the Azimuth, and the second number, after the slash, is the Altitude. NOTE: If your version of Stellarium lists TWO lines with Az/Alt information, use either one – the difference between the two is very small, and we don’t need to worry about what that difference is. • What are the Azimuth and Altitude of your star? ROUND OFF ALL YOUR AZIMUTH AND ALTITUDE READINGS TO THE NEAREST DEGREE – IN OTHER WORDS, IGNORE EVERYTHING AFTER THE “°” SYMBOL! Az 185__________ Alt 4____________ Try a few other stars along the horizon . Click on them. Look at their altitudes. Compare the answers to what you saw for your first star. Do you notice a pattern? • What is the value of altitude for any star on the horizon? 8________________° Now find a star that is straight above one of the stars you just chose. In other words, look a little higher in the sky. Click on the new star. Note its altitude and azimuth, and compare them to the values for the stars just below them, on the horizon. One of the numbers will have changed, and the other will be (approximately) unchanged. • As you move the cursor straight up from the horizon (in other words, as you look up from the horizon, toward the zenith), which angle changes, Altitude or Azimuth? Altitude
changes___________________________ Zoom out and re-center the sky until you are looking at the entire sky at once. Click as close as you can to the zenith (the point at the center of the screen). Remember, the zenith is the point directly over your head in the sky. • What is the value of altitude at the zenith? 72_______________° Altitude is an angle that tells you where a star is above the horizon. Picture two rays coming from your head – one pointing at the horizon directly below the star, and the other pointing at the star you're looking at. The angle between those rays is the altitude of a star. Click the cursor on a star that is below the horizon – in other words, click on the ground. Notice the value of the altitude here. • How can you tell by looking at a star’s altitude whether it is above or below the horizon? You can tell that the star’s altitude will be greater than 0 if it is above the horizon. If the stars altitude is below 0, it is below the horizon.__________________________________________________________________________ Go back and click on a few more stars on the horizon . • As you click left or right along the horizon , which angle changes, Alt or Azm? Azimuth changes___________ Click around the entire horizon (you may have to move the horizon by grabbing it with the cursor and dragging it), and watch the Azimuth change. Drag the sky around so you're looking at the Northern horizon. Click on various places on the horizon just to the left and right of North , and look at the values of altitude and azimuth for various points on the horizon. • What is the maximum value of azimuth? 357______________° • What is the azimuth of E? 89__________° W? 270___________° S? 180___________° NW? 314___________° Azimuth measures the angle along the horizon in degrees, to your chosen star, starting at North and going clockwise. Find the star Polaris, using Stellarium's Search window (or by using CTRL-F or the F3 key). • What are the azimuth and altitude of the star Polaris ? Az 359_____________° Alt 34_____________° • What is the latitude here in L.A., where you are observing from? (To find your latitude, open the Location window – your latitude and longitude are listed there) 34_________________________° • Comparing the answers to the previous two questions, what might you guess is the relationship between an observer’s latitude and the altitude of Polaris above his or her horizon? The observers latitude may be the same as the Polaris at any given location._______________________
Stellarium can superimpose a grid on the sky that allows you to easily measure Altitude and Azimuth. To show this grid, press the “ Z ” button on your keyboard (or go to the toolbar at the bottom of the screen and click on Azimuthal Grid) . The lines in the grid that run parallel to the horizon are lines of altitude, measuring from the horizon to the zenith, and the lines that are perpendicular to the horizon, and which all meet at the zenith like the spokes of a wheel, are lines of azimuth, measuring along the horizon, from North. The grid lines are labeled, in degrees where they hit the edge of the screen. Set the time for 8 PM tonight by changing the time in the Date/Time window. Label the brightest stars by opening the View window and putting a check next to Stars in the Labels and Markers section of the Sky sub-menu. Also, move the slider next to Stars to about half way from the left. Close the View window. It's in the end of the bowl of the Big Dipper in the constellation Ursa Major . Look for Ursa Major , and then click on the end star in the bowl of the Big Dipper to make sure you've found Dubhe. Don't forget, if you want to see the constellation outlines and names on the screen, press C and then V . • What is Dubhe’s Az and Alt at 8 PM ( Remember, if you click on a star, its data will be shown onscreen!) ? Az _21_______________° Alt _11__________________° Change your location to New York City ( Lat=41º N, Lon=74º W ) in the Location window by entering New York in the search box and then scrolling down until you find New York, United States in the resulting list and clicking on it. • Find Dubhe's azimuth and altitude in New York AT THE SAME TIME AS THE PREVIOUS QUESTION. Az 37____________° Alt 41______________° • Are Dubhe's Altitude and Azimuth the same in New York and L.A. at the same time? Why or why not? The Dubhe’s Alt and Az are different in LA than in NYC. This is because these are two separate locations on opposite ends of a large country.___________________________________________________________________________ Change your location back to Los Angeles , and the date back to today's date, at 9 PM . • Back in L.A., what is Dubhe’s Azimuth and Altitude at 9 PM ? Az 29__________° Alt 21___________° • Do a star's azimuth and altitude stay constant as the night goes on? The Alt increases as the night goes on.____________________ • What is Polaris' altitude and azimuth at 8 PM? Az 0_________° Alt 34_________° • What about at 9 PM? Az 359_________° Alt 34_________° • Why does Dubhe behave differently from Polaris? Polaris’ Az has a major increase from 8PM to 9PM, unlike Dubhe._____________________________________________________________________________ ______ • If someone told you they saw a satellite at 85 degrees altitude, where would you look (circle one)? • Near the horizon • Near the Zenith • Halfway up the sky
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