Observing Projects
An excellent resource for learning how to observe variable stars is the Web site of the American Association of Variable Star Observers. A wealth of data about specific variable stars can be found on the Sky & Telescope Web site and in the three volumes of Burnham’s Celestial Handbook: An Observer’s Guide to the Universe Beyond the Solar System (Dover, 1978). This book also provides useful information about observing star clusters.
Use Starry Night™ to demonstrate your knowledge of the evolution of a main sequence star. Open Favourites > Explorations > Stellar Evolution. The view shows the sky as seen from the center of a transparent Earth with the constellations displayed and five labeled stars. Use the File menu (Windows) or Starry Night menu (Mac) to access Preferences…, open the dropdown menu and set the Cursor Tracking (HUD) options to show Radius, Luminosity, and Spectral class. Open the Status pane and expand the Hertzsprung-Russell layer to show the H-R diagram for all of the stars within this view. Now position the cursor over each of the labeled stars and form a table of values of the above parameters for each star. Using this information and the position of the star in the H-R diagram (appearing as a red dot in the diagram when the cursor is over the star), sort and list the labeled stars in increasing evolutionary age.
Use the Starry Night™ program to look for signs of stellar evolution in M101, the Pinwheel Galaxy. Select Favourites > Explorations > Atlas and open the Find pane. Type M101 in the search box and then right-click (Ctrl-click on Mac) on M101 in the list and select Magnify from the contextual menu. (a) What is the color of the central part of this Galaxy? (b) What is the color of the outer regions of this galaxy? (c) Based on your observations, what type of stars would you expect to predominate in each of these two regions of this galaxy?
Collaborative Exercises
The inverse relationship between a star’s mass and its main sequence lifetime is sometimes likened to automobiles in that the more massive vehicles, such as commercial semi–tractor-trailer trucks, need to consume significantly more fuel to travel at highway speeds than more lightweight and economical vehicles. As a group, create a table called “Maximum Vehicle Driving Distances,” much like Table 19-1, “Main-Sequence Lifetimes,” by making estimates for any five vehicles of your groups’ choosing. The table’s column headings should be (1) vehicle make and model; (2) estimated gas tank size; (3) cost to fill tank; (4) estimated mileage (in miles per gallon); and (5) number of miles driven on a single fill-up.
Consider Figure 19-20, showing the period-luminosity relation for Cepheids. If a certain Cepheid star has an average luminosity of 4×1030 W, what is the variable star’s approximate period?
Figure 19-18a shows a light curve of apparent magnitude versus time in days for δ Cephei—a pulsating star that reaches maximum brightness every 5.4 days. Create a new sketch of apparent magnitude versus time in days showing three different stars: (1) δ Cephei; (2) a slightly smaller pulsating star; and (3) a slightly larger pulsating star, all of which have about the same total change in apparent magnitude.