Big Dipper II

Follow this procedure:

• Pick a time well after sunset to make your observations; you will make the observations at the same time each night you go out. Make sure that the time you pick is late enough to always be after sunset (particularly in the spring, when the days are getting longer).
• Your observing location should have a good clear view of the northern horizon, without any tall obstacles in the way (trees, buildings, etc.). You will make all your observations from the same location.
• Download and print the file PolarPlot.pdf, and use this to record your sketches. The North Star should be plotted in the middle of the circles. The interval between one circle and the next is 10° (one fist).
• Each time you observe the Big Dipper, carefully plot the position of the seven stars that make up the dipper. Use your hands/fists to measure angles in the sky. Be very careful to plot each star correctly in relation to the others and in relation to the North Star. Also record the date and time of your observations.
• Repeat the observation/sketch procedure every 7-10 days for two months. Don't worry about the occasional cloudy night; get the observations at the first clear opportunity.
• Note that over the course of your observations, the stars should not change their distance away from one another or away from the North Star. Rather, they should seem to rotate around together in a circle.

• Using your sketch log, measure the total number of degrees that the Big Dipper has rotated around the North Star.
• Divide 360° by the number of degrees that the Big Dipper rotated during your observations. Multiply the result by the number of days between your first and last observations.
• If you have been careful, your answer should be close to the number of days in a year. Is your result close? If not, why not? Explain as completely as you can.
• Be sure to follow the general instructions applicable to all projects.

• If you have a suitable camera with a tripod and know how to use it, you can take photographs of the stars instead of making sketches. The camera must be capable of making time exposures of at least several seconds. Almost any digital SLR camera can do this, as can some digital point-and-shoot cameras (including most Canon models). A film camera with a locking shutter or cable release will also work. Before attempting to do this project with a camera, please bring the camera to your instructor to determine whether it is suitable, and to discuss what settings to use.
• A wide angle lens (or a zoom lens at its widest setting) is best. Even so, you may not be able to fit all of the Big Dipper into the field of view. That's ok as long as enough other stars are visible. Aim the camera so the North Star is at the center of the field of view, with at least one terrestrial object (perhaps a tree or rooftop) also visible. Be sure to note carefully how the camera is aimed, because you'll need to set it up exactly the same way for each observation. Take a photo every seven to ten days, at the same time each night, over the course of two months.
• Before printing your photos, it's best to invert them (switching black and white) in Photoshop or a similar program. Your instructor can help with this.