Exam 17: The Nature of the Stars

Light, leaving a point source, spreads out so that the apparent brightness, b, of light per unit area varies with distance d according to which law ( $\alpha$ means "proportional to")?

What is the luminosity of a white dwarf star with the same surface temperature as the Sun? (See Figure 17-15a.(in the text))

A luminosity function is a plot of the:

Brown dwarf spectral classifications, in order of increasing temperature, are:

Which characteristic of a star's spectrum is most important in determining its spectral classification?

The luminosity of a star is:

The relationship between the luminosity of a star, L, its surface temperature, T, and its radius, R, is given (with $\sigma$ = Stefan-Boltzmann constant) by:

The absolute magnitude of the Sun is +4.8 and its luminosity is 3.9 × 10²⁶ watts. The absolute magnitude of the star $v$ (Nu) Hydrae is -0.2. What is the luminosity of $v$ Hydrae?

Suppose that, at night, the brightness of a light bulb is measured from a certain distance and then the light bulb is moved to a distance twice as far away. How bright will the light appear compared to the earlier measurement?

Two stars orbit each other in a binary system. Each star by itself has an apparent magnitude of 4.0. What is the apparent magnitude of the two seen together as a single object?

If a star moves in space, its proper motion appears as an angular displacement against the background stars. Its parallax motion also appears as an angular displacement against the background stars. How can we tell the difference?

What is the physical reason for the appearance of periodic splitting and recombining of spectral lines in the spectra of binary stars?

Using Figure 17-15a, what can you conclude about the star Mira compared to the Sun?

In the Hertzsprung-Russell diagram of Figure 17-15a, which of the following is the correct sequence of stars in order of increasing intrinsic brightness?

The proper motion of a star is:

Observations of binary stars have helped astronomers to determine which important scientific parameter?

Figure 17-5 shows a typical luminosity function. This shows that:

Stellar parallax is used to determine which of the following properties of a nearby star?

Neptune is about 1.5 times as far from the Sun as is Uranus, and it is about the same size. About how much radiant energy does Neptune receive from the Sun, compared to Uranus?

The luminosity of a star is: