1. The relation between the parallax angle p (in arcseconds) and the distance d (in parsecs) to a star is

d = 1/(__________) = __________ parsecs.

d = 1/(__________) = __________ parsecs.

2. If a star has apparent magnitude m and absolute magnitude M, then the distance d (in parsecs) to the star is

d(parsecs) = 10^{[m - M + 5]/5}

and so d = 10^{[m - M + 5]/5} = __________ parsecs.

and so d = 10^{[m - M + 5]/5} = __________ parsecs.

and so d = 10^{[m - M + 5]/5} = __________ parsecs.

3. On the Hertzsprung-Russell diagram shown at right, identify

(a) the main sequence;

(b) the region of giant stars;

(c) the region of supergiant stars;

(d) the region of white dwarf stars;

(e) the position of the Sun; and

(f) the position of a star with 100 times Sun's luminosity, but with the same temperature as the Sun.

4. An O star, a G star, and an M star are on the main sequence of the Hertzsprung-Russell diagram.

Which star is hottest? _____

Which star is coolest? _____

Which star has the largest luminosity? _____

Which star has the smallest luminosity? _____

Which star is most massive? _____

Which star is least massive? _____

Which star is most like the Sun? _____

5. The total energy per second emitted by a star is called the star's luminosity. The luminosity of a star depends both on the star's _______________ and the star's surface _______________. The ratio of the luminosities L_A and L_B of two stars A and B is related to their radii (R_A and R_B) and their surface temperatures (T_A and T_B) by

This means that if star A is 5 times larger than star B, and if star A has twice the surface temperature of star B, then

L_A/L_B= (_____)² (_____)⁴ = _____.

Thus a star with 5 times the Sun’s radius and twice the Sun’s surface temperature has __________ times the Sun’s luminosity.

6. Kepler's 3rd law, as derived by Newton, says that a³/P² = M₁ + M₂, where a is the semimajor axis of the orbit of the two stars (in AU), P is the period of the orbit (in years), and M₁ and M₂ are the masses of the two stars (in solar masses).  Suppose the semimajor axis of a binary star system is a = 4 AU and the period is 2 years.  Then the sum of the masses of the two stars is M₁ + M₂ = a³/P² = (_____)³/(_____)² = _____ solar masses.  Also suppose, from observing the orbits of the two stars about their barycenter (center of mass), we know that star 1 is three times more massive than star 2; that is M₁ = 3M₂.  Then we can conclude that M₁ = _____ solar masses and M₂ = _____ solar masses.

7. A binary star system (an orbiting pair of stars) may be too far away to be seen as two separate points of light. However, the spectrum of the binary star system may be used to detect the presence of two stars. The spectral lines of the star moving toward Earth will have a __________ shift, and the spectral lines of the star moving away from Earth will have a __________ shift. This pattern of Doppler-shifted spectral lines moves back and forth during every orbital period. Such a system is called a _______________ binary system. If the two stars eclipse (move across) each other, the _______________ and the _______________ of each star can be determined.

8. An emission nebula (also called an _____ region) is a huge cloud of _______________ gas that glows a characteristic pinkish red. These nebulae are powered by the _______________ light emitted by nearby, very hot stars, and are frequently seen surrounding sites of active star formation. A reflection nebula is produced when starlight is _______________ from a huge cloud of dust; it has a characteristic __________ color.

9. Stars are formed in _______________ _______________, cold (10 K), dense interstellar clouds of gas and dust that light cannot penetrate. A __________ is the hot core of a collapsing dark nebula. Nuclear __________ reactions have not yet started at its center, so it is not yet a star. Its light and heat come from the conversion of gravitational/thermal energy (circle one) into gravitational/thermal energy (circle one). When the center finally becomes hot and dense enough, nuclear __________ reactions begin, producing the light and heat of the newly born main-sequence __________. Dark nebulae are found in the giant _______________ _______________ that populate the spiral arms of our Milky Way galaxy.

10. When nuclear __________ reactions are about to begin in the center of a protostar, the protostar may eject huge amounts of gas into space. Low-mass stars that vigorously eject gas are called _______________ stars. Our Sun went through a _______________ phase as it became a main-sequence star. If the protostar is surrounded by a disk of gas and dust called an _______________ _______________, the ejected gas may be focused into two fierce __________ of gas that are directed perpendicular to the _______________ _______________.

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