If you own a laptop, please bring it to class. You will use Stellarium and submit your answers on Cobra using the answer sheets. (Word, RTF).
The Stellarium shortcuts you used in the first lab are on the inside cover of your lab packet and by clicking here.
If you are using your own computer, be sure it is set for the Central Time Zone. Check the video links to make sure your PC or Mac have the correct settings.
Pre-Lab Assignment: You will be using Stellarium to examine the daily and annual motions of stars. Answer these questions before coming to lab.
A) Why is the North Star so important?
B) What is a "constellation" as opposed to an "asterism"?
C) During which seasons can you find the Big Dipper in the sky, as seen from Champaign?
D) Why is it important to have constellations? What good are they?
Introduction: After familiarizing yourself with Stellarium last week, you will now use it to determine the location of some of the more popular constellations as viewed from our latitude on Earth. It should be very valuable in your own observations of the sky and in learning a few constellations. I recommend using it to prepare for your sky quizzes! Your answers should be typed. You may use the answer sheets. (Word, RTF)
The Stellarium shortcuts you used in the first lab are on the inside cover of your lab packet and by clicking here.
Procedure: Start Stellarium. You can take the software out of full-screen mode. You should have the location set to Champaign by default on the software. Set the initial conditions to the following:
Date: September 7 (09-07) of the current year
Time: 21:00:00 UTC-05:00 (9:00 PM CDT)
Open the Configuration window and select the Information tab. Uncheck every box for the "Displayed fields" except the following: Name, Visual magnitude, Altitude/Azimuth, and Type. Close the Configuration window.
Keep the field of view at 60˚. Turn off the ground and turn on the horizon and the ecliptic. Display the constellation names and boundaries. Turn on the azimuthal grid. This will show you altitude and azimuth for the local sky. Move the sky so the zenith (90˚ Alt) is at the center of the field of view.
1. What two bright stars can be found near the zenith with altitudes greater than 70°? Brighter stars have bigger circles, and if a star has no label, you can identify it by selecting it with the cursor.
2. What constellations are each of these two stars located in?
3. The ecliptic runs through the thirteen Zodiac constellations. What two constellations of the Zodiac are currently rising in the east? (It may help to see the constellation artwork as well.)
The Big Dipper is an asterism of the seven brightest stars in Ursa Major. If you're looking at the artwork of Ursa Major, the Big Dipper is the hindquarters and tail of the big bear. The two "pointer stars" of the Big Dipper are Merak and Dubhe, because they "point" to Polaris in the Little Dipper, part of Ursa Minor.
4. What direction would you look to see the Big Dipper at that time? Is the Big Dipper above or below Polaris? Is it left or right of Polaris?
5. Turn off the atmosphere and change the time to determine how many stars of the Big Dipper set in Champaign.
Consider the terms for the motions of stars we discussed in class and are found in Chapter 2.
6A. What is the term for the motion shared by the North Star and the Big Dipper in Champaign?
6B. As you change the time, what distinguishes the North Star from every other object in the sky?
Look at the motion of the stars at the eastern horizon and at the western horizon.
7. Roughly how often do the stars rise and set?
8. Reset the date and time to 09-07 21:00. What is the name of the bright star that is nearly due west at about 25˚ altitude?
9. What is the name of the bright star (not a planet) nearly southwest at about 15˚ altitude?
10. What time (rounded to the nearest hour) does the star in Question 9 set on September 7?
The keyboard shortcuts allow you to toggle the displays of stars, Solar System objects, and the Milky Way.
11. The planets appear to move against the background stars and hence won't be in the same place from month to month. We find the planets in the Zodiac constellations. What planets are visible (above the horizon) to the naked eye (magnitude less than 5) on September 7 at 21:00 and in what constellations are they located? If there are none, what constellation is Venus located in at that time?
You may have difficulty seeing the whole band of the Milky Way. Make sure the atmosphere is turned off, and you can change the Milky Way's brightness in the Sky and viewing options window.
12. On September 7 at 9 PM, the Milky Way runs across the sky and meets the horizon at two points. What are the azimuth values at these two points?
13. Explain why we would have a difficult time seeing the star Spica on September 7?
14. The brightest star other than the Sun is Sirius. What time, rounded to the nearest hour (5:30 is rounded to 6:00), does Sirius rise on September 8 and in what cardinal direction should we look for it?
Now you should be at least somewhat familiar with the sky from Champaign. However, the appearance of the sky does change depending on where you are on the Earth. Specifically, changing latitudes changes the stars and constellations that can be seen.
Make sure the atmosphere is still turned off, and that your field of view is facing north. Turn off the azimuthal grid and turn on the constellation lines and labels.
Find the Big Dipper in the northern sky. Click the Fast Forward button about four times and watch as the Big Dipper moves around in the sky.
|
Typing the degree symbol (°):
PC: Make sure the Number Lock is turned on. Hold the Alt key and type 0176 on the keypad. Mac: Type Opt-K. All computers: Copy (Ctrl-C) and paste (Ctrl-V) the symbol shown above. |
15A. Which star of the Big Dipper reaches the lowest altitude
as the asterism moves?
15B. Record the lowest altitude of that star rounded to the nearest degree
(round up at 30' or more).
15C. Use the Location window to record the rounded latitude of Champaign. (Latitudes
require you to specify "north" or "south".)
15D. What is the altitude of Polaris in Champaign to the nearest degree?
Change your viewing location to Edmonton, Canada in the Location window.
16A. What is the latitude of Edmonton to the nearest degree?
If the atmosphere turned on when you changed the location, turn it off again. Set the motion to fast forward again and then stop the motion when the star from question 15 reaches its lowest altitude. Make sure the star is selected before answering question 16B.
16B. What is the lowest altitude of the star rounded to the nearest
degree?
16C. What is the altitude of Polaris in Edmonton rounded to the nearest degree?
17A. Subtract between the altitudes of the star in Edmonton and Champaign.
17B. Subtract between the latitudes of Edmonton and Champaign.
17C. Subtract between the altitudes of Polaris in Edmonton and Champaign.
Now, change your location to Tromsø, Norway. Repeat the procedure above, finding the lowest altitude of the star from Question 15.
18A. What is the latitude of Tromsø to the nearest degree?
18B. What is the lowest altitude of the star rounded to the nearest
degree?
18C. What is the altitude of Polaris in Tromsø to the nearest degree?
If you haven't already noticed, each time you've changed your location, you've moved farther north.
19A. Subtract between the altitudes of the star in
Tromsø and Edmonton.
19B. Subtract between the latitudes of Tromsø and Edmonton.
19C. Subtract between the altitudes of Polaris in Tromsø
and Edmonton.
20. Describe what happens to the minimum altitude of the star from question 15 as you move farther north. Why is this the case?
21. If you were to move 1˚ farther south on Earth, what would happen to the minimum altitude of this star?
Now, let's move southward. Set your location to Houston, Texas.
22A. What is the latitude of Houston to the nearest degree?
22B. What is the altitude of Polaris as seen in Houston?
Let's revisit Question 5.
23. How many stars of the Big Dipper set in Houston?
At this location, you should notice that the Little Dipper is still circumpolar. The star Pherkad is the one which will reach the lowest altitude.
24. Find the altitude of Pherkad when it is at its lowest in the sky in Houston.
25. Estimate the latitude rounded to the nearest degree where observers will see Pherkad barely touch the horizon at its lowest altitude. (Look back at Question 21 for guidance.)
26. Explain how the motions of stars in the sky change for different locations on Earth.
27. How can you use the altitudes of stars to determine your latitude?