Suppose you are on a strange planet and observe, at night, that the stars do not rise and set but circle parallel to the horizon. Now you walk in a constant direction for 8000 miles, and at your new location on the planet you find that all stars rise straight up in the east and set straight down in the west, perpendicular to the horizon.
What is the semimajor axis of a circle of diameter 24 cm? What is its eccentricity?
What would be the period of a planet whose orbit has a semi-major axis of 4 AU? Of an asteroid with a semimajor axis of 10 AU?
Where are you on the Earth according to the following descriptions? (Refer back to Chapter 1 as well as this chapter.)
What distinguishes one type of electromagnetic radiation from another? What are the main categories (or bands) of the electromagnetic spectrum?
What type of electromagnetic radiation is best suited to observing a star with a temperature equivalent to:
Why is it dangerous to be exposed to x-rays but not (or at least as much) dangerous to be exposed to radio waves?
How many times brighter or fainter would a star appear if it were moved to
Suppose that a spectral line of some element normally at 500 nm (1 nm = 0.000000001 metres), is observed in the spectrum of a star to be at 500.1 nm. How fast is the star moving toward or away from the Earth?
Compare the eye, photographic film, and CCD's as detectors of light. What are the advantages and disadvantages of each?
Why do astronomers place telescopes in Earth orbit? What are the advantages for different spectral regions?
Make a sketch of the Sun's atmosphere showing the locations of the photosphere, chromosphere, and corona. What is the approximate temperature of each region?
Why do sunspots look dark?
Suppose an eruptive prominence rises at a speed of 150 km/sec. If it does not change speed, how far from the photosphere will it extend after 3 hours? How does this distance compare with the diameter of the Earth?
Give some everyday examples of the transport of heat by convection and by radiation.
Explain why color is a measure of a star's temperature. [It might be useful to look at Table 8.1 in the text or the table of spectral types that can be found in the course handouts.]
What are the approximate spectral classes for stars whose wavelength of maximum light (lamda_max) have the following values:
Find the combined mass of two stars in a binary system whose (orbital) period of mutual revolution is two years, and for which the semimajor axis (separation) of the relative orbit is 2 AU.
An astronomer discovers a type M star with a large luminosity. How is this possible? What kind of star is it?
A star has a temperature of 10,000K and a luminosity of 10^{-2} L_sun (= 0.01 solar luminosities). What kind of star is it?
The evolutionary track for star with one solar mass remains nearly vertical in the HR diagram for a while (see figure 12.12). How is its luminosity changing during this time? Its temperature? Its radius? What is its source of energy?
Suppose an astronomer told you she had found a type O main sequence star that contained no elements heavier than helium. Would you believe her? Why?
Would you be more likely to observe a Type II supernova (the explosion of a massive star) in a globular cluster or in an open cluster? Why?
Astronomers believe there are something like 100 million neutron stars in the galaxy. Yet we have found only about 1000 pulsars in the Milky Way. Give several reasons why these numbers are so different. Explain each reason.
Which is likely to be more common in our Galaxy -- white dwarfs or black holes? Why?
Consider the following five types of objects: (1) open cluster, (2) giant molecular cloud, (3) globular cluster, (4) group of O and B stars, and (5) planetary nebulae. a) Which occur only in spiral arms? b) Which occur only in the parts of the Galaxy other than spiral arms? c) Which are thought to be very young? d) Which are thought to be very old? e) Which have the hottest stars?
Where in the Galaxy would you expect to find Type II supernovae, which are the explosions of massive stars and that go through their lives very quickly? Where would you expect to find Type I supernovae which involve the explosions of white dwarfs?
Starting with the determination of the size of the Earth, outline the sequence of steps necessary to calculate the distance to a remote cluster of galaxies. (Hint: Review Chapter 18.)
Suppose a supernova explosion occurred in a galaxy at distance of 10^8 lightyears. If we are only now detecting it, how long ago did the supernova actually occur? According to Hubble's law, what is the velocity with which this galaxy is moving away from us? (Assume a Hubble constant of 20 km/second per million lightyears.)
A friend of yours who has watched many Star Trek episodes says, "I thought that black holes pulled everything into them. Why then do astronomers think that black holes can explain the great outpouring of energy from Quasars?" How would you respond?
Why do we know less about the formation of galaxies than about the formation of stars?
Suppose the universe expands forever. Describe what will become of the radiation from the primeval fireball. What will the future evolution of galaxies be like? Could life as we know it survive forever in such universe? Why?