NORTH SKY CONSTELLATIONS
This lab is written for people living in the Northern Hemisphere. If you are in the Southern Hemisphere, you must get a star chart and determine the Southern constellations to use for this exercise. If you live in a city, only a few stars will be visible because of the glare from the lights. For most cities, you can still make some significant observations with what you see. If you wish to learn constellations, get a copy of Sky and Telescope or Astronomy magazines from the library or newsstand. A star chart that also tells the location of any visible planets will be in the magazine.
**ALTERNATIVE EXERCISE: If you have difficulty seeing constellations from in town or if the weather remains cloudy for many days in a row, I suggest that you simulate this lab using an online computer program showing the night sky. Several can be downloaded for free. Use a search program (e.g., Google) and type in the name, “Skyglobe”, “Stellarium” or general terms such as “night sky chart.” Each program has unique operating procedures that must be learned in order to observe the simulated movement of the north sky over the course of 24 hours. Following are instructions for the program “Skyglobe”.
Once you have “Skyglobe” running, set the location to your own position by typing “L” and then selecting the city that is closest to you. Next, advance the time to early evening by pressing the “H” key once for each hour of time. Finally, press “N” for a view of the north sky. You can locate the Little and Big Dippers along with Cassiopea and watch them change location as you advance the time hour by hour. For further observations of the eastern and western skies, type “E” or “W.” A. OBJECTIVES The intent of the exercise is to show the observer that the night sky appears to revolve overhead. This is actually due to the earth’s rotation. B. BACKGROUND The stars appear to change position in the sky during the night due to the earth’s rotation. You will not detect this motion during a short period of observation, but the stars will make a complete revolution through the sky during a 24-hour period. They are back at their starting position by the next night at the same time, so you probably think the sky never moved. The stars in the northern sky follow a circular path, revolving around a central pivot, the North Star (Polaris). If you kept a camera lens open all night while pointed at the north sky, the star tracks would make a big circle of light. Three to five constellations are always visible in the northern sky, depending on the amount of city glare. These are Ursa Major (Big Dipper), Ursa Minor (Little Dipper), Cassiopeia, Cephus, and Draco. In the summer, the Big Dipper is dominant, and in winter, Cassiopeia (shaped like a crooked “W”) is most obvious. 18
C.
EQUIPMENT You may need a compass to determine north unless you have a grasp of local direction.
D.
PROCEDURES 1. Locate the North Star by one of the following methods (it is not very bright, so you will have to work at it): a. The North Star should be almost due north at an elevation in the sky equal to the latitude of your location. (If you live in Denver at 40oN, the North Star will be 40o up from the horizon.) The two end stars of the Big Dipper are the pointing stars. See Figure 1 for a sketch of the Big Dipper. Draw an imaginary line through the pointing stars, and they will lead you to the North Star. There is a third method if your sky is relatively dark (not much glare). You may be able to see the entire Little Dipper. It is smaller and curved differently than the Big Dipper. The North Star is the last star in the handle of the Little Dipper. * * * Big Dipper * * * * * * * * * Pointing stars ———– * ——- * —————————————> Figure 1 * North Star Little Dipper
b.
c.
2.
Picture the north sky as the face of a clock with the NORTH STAR in the center. Think of the Big Dipper and Cassiopeia as hands on this imaginary clock, and record the “imaginary hour” to which they point. Come back two hours later, and make the same observation. If possible, go out again two hours later OR get up before sunrise and make the same observation.
3.
Go out the next night at the same time you started, and observe once more. 19
E.
RESULTS AND CONCLUSIONS Send in your table of observations, and summarize what you observed. Which way were the stars appearing to rotate (clockwise or counterclockwise)? If the northern stars go through a complete rotation every 24 hours, how far on the imaginary clock do they move every hour of real time? The stars in the rest of the sky do not rotate in a circle but rise from the eastern horizon and set beyond the west. Why do the northern stars appear to take a different path?
F.
APPLICATIONS 1. 2. If you lived at the equator (Latitude 0o), where would you find the North Star? If you lived in Buenos Aires, Argentina (Latitude 34oS), where would the North Star be, and what would you see when you looked at the north sky?
laboratory report should contain the following sections: (1) Hypothesis, (2) Procedures,
(3) Observations and Results, and (4) Conclusions. Make certain you include all four headings with at least a short paragraph for each. In addition, tables, graphs, and answers to questions may be necessary in the latter two sections.
HYPOTHESIS
Scientific research should contain a preliminary statement of the expected outcome of the experiment. This can include predictions of the specific experiment or the general anticipated result. If you are merely doing an observation and have no idea of the outcome, you cannot make an actual hypothesis. Instead, make a short statement of the purpose of the observation. However, if you have preconceived ideas of the outcome, include them in this section, and then see how they compare to the results.
PROCEDURES
Even though you are told what to do, write a paragraph of the specific steps you actually took in doing the experiment or observation. Because you are coming up with your own equipment, your procedures will be of particular interest.
OBSERVATIONS AND RESULTS
This is where you should make a detailed statement of the outcome of your experiment. Record all your pertinent observations in a clear, readable form. Arrange your data in tables (such as measurements and calculations you make). Answer any questions asked in this Study Guide, marking these clearly so that they can be easily found.
CONCLUSIONS
Your conclusions should include a comparison between the outcome of the experiment and your initial predictions made in the hypothesis. In cases where you are attempting to recreate a physical constant, compare your number to the accepted value, using the formula for experimental error:
Experimental Error Equation
If you find a large difference in your results from the expected value or if your anticipated observations are not the same as your actual observations, try to identify possible sources of error or reasons for the difference in the hypothesis and results
