Activities

Observing Projects

  1. Turn on an electric stove or toaster oven and carefully observe the heating elements as they warm up. Relate your observations to Wien’s law and the Stefan-Boltzmann law.

  2. Use Starry Night to examine the celestial objects listed below. Select Favourites > Explorations > Atlas to show the whole sky as would be seen from the center of a transparent Earth. Ensure that deep space objects are displayed by selecting View > Deep Space > Messier Objects and View > Deep Space > Bright NGC Objects from the menu. Also, select View > Deep Space > Hubble Images and ensure that this option is turned off. To display each of the objects listed below, open the Find pane and then type the name of the selected object in the edit box and press the Enter (Return) key. The object will be centered in the view. Use the zoom controls to adjust your view until you can see the object in detail. For each object, decide whether you think it will have a continuous spectrum, an absorption line spectrum, or an emission line spectrum, and explain your reasoning. The objects to observe are (a) the Lagoon Nebula in Sagittarius (with a field of view of about 6° × 4°, you can compare and contrast the appearance of the Lagoon Nebula with the Trifid Nebula just to the north of it); (b) M31, the great galaxy in the constellation Andromeda (Hint: the light coming from this galaxy is the combined light of hundreds of billions of individual stars); (c) the Moon (Hint: moonlight is simply reflected sunlight).

  3. Use the Starry Night program to compare the brightness of two similarly sized stars in the constellation Auriga. Select Favourites > Explorations > Auriga. The two stars Capella and Delta Aurigae are labeled in this view. Select Preferences from the File menu (Windows) or Starry Night menu (Mac) and set Cursor Tracking (HUD) options so that Temperature and Radius are shown in the HUD display. You will notice that these two stars have the same radius but differ in temperature. From these data, which of these stars is intrinsically brighter and by what proportion?

  4. Use Starry Night to examine the temperatures of several relatively nearby stars. Select Favourites > Explorations > Atlas. Use the File menu (Starry Night menu on a Mac) and select Preferences… to open the Preferences dialog window. Click the box in the top left of this dialog window and choose Cursor Tracking (HUD). Scroll through the Show list and click the checkbox next to Temperature to turn this option on. Then close the Preferences dialog window. Next, open the Find pane, click the magnifying glass icon in the edit box at the top of this pane, and select Star from the dropdown menu. To locate each of the following stars—Altair; Procyon; Epsilon Indi; Tau Ceti; Epsilon Eridani; Lalande 21185—type the name of the star in the edit box and then press the Enter (Return) key. Use the HUD to find and record the star’s temperature. (a) Which of the stars have a longer wavelength of maximum emission λmax than the Sun? (b) Which of the stars have a shorter λmax than the Sun? (c) Which of the stars will have a reddish color?

  5. You can use the Starry Night program to measure the speed of light by observing a particular event, in this case one of Jupiter’s moons emerging from the planet’s shadow, from two locations separated by a known distance. These two locations are at the north poles of Earth and the planet Mercury, respectively. Open Favourites > Explorations > Io from Earth. The view shows Jupiter as seen from the north pole of Earth at 9:12:00 p.m. standard time on September 25, 2010. You will see the label for Io to the left of the planet. Keep the field of view about 11 arcminutes wide. Click the Play button and observe Io suddenly brighten as it emerges from Jupiter’s shadow. Depending upon your computer monitor, you may need to Zoom out slightly so that Io’s transition from being invisible to visible occurs instantaneously (at high zoom levels, Io will brighten gradually). Next, use the Time controls to Step time backward and forward in 1-second intervals to determine the time to the nearest second at which Io brightens. Open the Status pane and expand the Time layer. Record the Universal Time for this event. Then open the Info pane and be sure that Io Info appears at the top of the Info pane. Expand the Position in Space layer and record the value given for Distance from Observer. Now select Favourites > Explorations > Io from Mercury. This view once again shows Io labeled to the left of Jupiter but in this instance you are viewing the scene from the north pole of the planet Mercury. With the field of view set to 11 arcminutes wide, click the Play button. Stop time flow as soon as you see Io suddenly brighten as it emerges from eclipse. Again, it may be necessary to adjust the zoom level to make this event appear instantaneous rather than gradual. Use the time controls to find the time to the nearest second at which Io brightens. Open the Status pane and record the Universal Time for this event as seen from Mercury. Then open the contextual menu for Io and select Show Info. Record the Distance from Observer of Io from the Position in Space layer. Use your observations to calculate the speed of light. First, calculate the difference in the time between the two observations in seconds. Then calculate the difference in the Distance from Observer in AU for each of the locations. Divide the difference in the distance by the difference in time to calculate the speed of light in AU per second. Finally, convert this value to kilometers per second by multiplying the result by 1.496 × 108 (the number of kilometers in 1 AU). How does your result compare to the accepted value of the speed of light of 2.9979 × 105 kilometers per second? Explain the difference between your calculated value from these observations and the accepted value for the speed of light.

Collaborative Exercise

  1. The Doppler effect describes how relative motion impacts wavelength. With a classmate, stand up and demonstrate each of the following: (a) a blueshifted source for a stationary observer; (b) a stationary source and an observer detecting a redshift; and (c) a source and an observer both moving in the same direction, but the observer is detecting a redshift. Create simple sketches to illustrate what you and your classmate did.