If no one has ever seen a star go through the complete formation process, how are we able to understand how stars form?
If an interstellar medium fills the space between the stars, how is that we are able to see the stars at all?
In Figure 11-2, what makes the nebula dark? What makes the Orion nebula glow?
Describe the energy source that causes a protostar to shine. How does this source differ from the energy source inside a main-sequence star?
In what ways is the internal structure of a 1-M⊙ main-sequence star different from that of a 5-M⊙ main-sequence star? How is it different from a 0.5-M⊙ main-sequence star? What features are common to all these stars?
How does the chemical composition of the present-day Sun’s core compare to the core’s composition when the Sun formed? What caused the change?
On what grounds are astronomers able to say that the Sun has about 5.4 × 109 years remaining in its main-sequence stage?
Explain how it is possible for the core of a red giant to contract at the same time that its outer layers expand.
Why does helium fusion require much higher temperatures than hydrogen fusion?
What does it mean when an astronomer says that a star “moves” from one place to another on an H-R diagram?
Explain how and why the turnoff point on the H-R diagram of a cluster is related to the cluster’s age.
What is the difference between Population I and Population II stars? In what sense can the stars of one population be regarded as the “children” of the other population?
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What are thermal pulses in AGB stars? What causes them? What effect do they have on the luminosity of the star?
How can an astronomer tell the difference between a planetary nebula and a planet?
What is a white dwarf? Does it produce light in the same way as a star like the Sun?
Some science-fiction movies show stars suddenly becoming dramatically brighter when they are “born” (that is, when thermonuclear fusion reactions begin in their cores). Discuss whether or not this is a reasonable depiction.
Eventually the Sun’s luminosity will increase to the point where Earth can no longer sustain life. Discuss what measures a future civilization might take to preserve itself from such a calamity.
Imagine that your group walks into a store that specializes in selling antique clothing. Prepare a list of observable characteristics that you would look for to distinguish which items were from the early, middle, and late twentieth century. Also, write a paragraph that specifically describes how this task is similar to how astronomers understand the evolution of stars.
Consider advertisement signs visible at night in your community and provide specific examples of ones that are examples of the three different types of nebulae that astronomers observe and study. If an example does not exist in your community, creatively design an advertisement sign that could serve as an example.
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 11-1: Approximate Main-Sequence Lifetimes, by making estimates for any five vehicles of your group’s 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.
Use the Starry Night™ program to observe the characteristics of several nebulae in the Milky Way Galaxy. Open Favourites > Explorations > Atlas and then select View > Galactic Guides > Equator from the menu to indicate the plane of the disk of the Milky Way Galaxy. Next, open the Find pane, click on the search box and select Nebulae from the list. For each of the following nebulae, type the name in the search box and press the Enter key and then click the icon next to the nebula in the list of found items and select Magnify from the menu: (a) NGC 7000 (the North America nebula); (b) M20 (the Trifid nebula); (c) M8 (the Lagoon nebula); and (d) M42 (the Orion nebula). Zoom in on each of these objects and describe your observations, noting the object’s distance from the galactic equator, and whether it is a dark, reflection, or emission nebula or some combination of these.
Use Starry Night™ to examine the H-R diagram of the Pleiades star cluster. This group of stars was formed relatively recently in astronomical time. Select Favourites > Explorations > Pleiades to display this cluster of young stars in the view. Click on the Status tab to display the H-R diagram of all stars in this field of view around the Pleiades. Note that this appears to be similar to that of stars in our local neighborhood. However, if you restrict the distance to display only the stars within this localized cluster, a different pattern emerges. Click on the Distance cut-off checkbox in the H-R Options layer of the Status pane to restrict the distance to a range between 320 ly and 420 ly. (a) Where on the H-R diagram do you now find the majority of the stars of this cluster? (b) In view of the existence within this cluster of very hot stars with high output of energy, what does this tell you about the age of this cluster compared to the general population of stars?
Use Starry Night™ to look for signs of stellar evolution in M101, the Pinwheel Galaxy. Select Favorites > Explorations > Atlas and open the Find pane. Click the icon in the search box and select Messier Objects from the list. Next, type M101 in the search box and then click the icon next to M101 in the list box 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?
Planetary nebulae represent the late stages of the evolution of stars whose masses are similar to that of the Sun. These nebulae are found throughout our Galaxy. You can use Starry Night™ to explore the distribution of these objects in our sky and to view several of these spectacular nebulae. Set the View for your home location at some time in the evening with a field of view of about 100°. Open the Options pane and expand the Deep Space panel. Expand the NGC-IC Database list, click in its box to activate the display of the objects in this list and click Off all entries in the list except Planetary Nebula. Use the hand tool to move around the sky. Note that these nebulae are mostly concentrated around the Milky Way in our sky. If you have access to a telescope, try to locate and observe several of these planetary nebulae, if possible on a clear, moonless night. Some of the more notable planetary nebulae include: Little Dumbbell (M76), NGC 1535, Eskimo, Ghost of Jupiter, Owl (M97), Ring (M57), Blinking Planetary, Dumbbell (M27), Saturn Nebula, and NGC 7662. If you do not have access to a telescope, use Starry Night™ to examine in detail two of these planetary nebulae, M57 (the Ring Nebula) and M27 (the Dumbbell Nebula), and compare their shapes and sizes. Select Favourites > Explorations > Atlas. Open the Find pane, click the icon in the search box and select Messier Objects from the list. Type the name of the nebula in the search box, then click the icon next to its name in the list box and choose Magnify to center upon and magnify the nebula in the view. (a) How do you account for the difference in the shape of these two planetary nebulae? (b) What is the nature of the central star in each of these nebulae?