Astronomy Chapter 11 quiz practice questions

What is the physical reason why astronomers can find the luminosity class (I, II, III, IV, or V) of a star using the star's spectrum? A) The wavelength of maximum emission (given by Wien's law) is affected by the size of the star. B) The relative amounts of hydrogen, helium, and other elements are different for stars of different luminosity classes. C) The absorption lines in the spectrum are affected by the density and pressure of the star's atmosphere. D) The absorption lines in the spectrum are affected by the star's surface temperature.

C) The absorption lines in the spectrum are affected by the density and pressure of the star's atmosphere.

Absolute magnitude is defined as the apparent magnitude that a star would have if A) all of the energy from the star were concentrated in the visual region. B) it were located at exactly 10 ly from the Earth. C) it were located at exactly 10 pc from the Earth. D) it were located at exactly 10 AU from the Earth.

C) it were located at exactly 10 pc from the Earth.

The relationship between mass and luminosity of stars on the main sequence is that A) the luminosity of stars increases with mass up to a peak around one solar mass, then decreases as the mass continues to increase. B) luminosity is independent of the stellar mass. C) the larger the stellar mass, the larger the luminosity. D) the greater the stellar mass, the less the luminosity.

C) the larger the stellar mass, the larger the luminosity.

To determine the sum of the masses of a visual binary star system, we need to measure A) the temperatures and periods of the stars. B) the distance from us and the semimajor axis of the orbit of one star relative to the other. C) the period and the semi-major axis. D) the temperatures and the distance from us.

C) the period and the semi-major axis.

The radial-velocity curve of a star in a binary star system is a plot against time of A) the speed of the star in a direction perpendicular to the line of sight to the star. B) the position of the star in celestial coordinates. C) the variation of Doppler shift of its spectral lines and hence of its speed toward or away from us. D) the temperature of the star as determined from the movement of the peak wavelength of its spectrum.

C) the variation of Doppler shift of its spectral lines and hence of its speed toward or away from us.

What are the two physical parameters of stars that are plotted in the Hertzsprung-Russell diagram? A) Mass and surface temperature B) Luminosity and mass C) Radius and mass D) Luminosity and surface temperature

D) Luminosity and surface temperature

What is spectroscopic parallax? A) The apparent change in position of the absorption lines in a star's spectrum due to the Doppler shift caused by the Earth's motion around the Sun B) The apparent change in position of a nearby star compared to distant background stars due to the motion of the Earth around the Sun C) The change in position of the absorption lines in a star's spectrum due to the Doppler shift caused by the star's motion around the center of mass in a binary star system D) The distance to a star measured using the spectral-luminosity class of the star and the inverse square law

D) The distance to a star measured using the spectral-luminosity class of the star and the inverse square law

The symbol He II refers to a A) helium atom that has lost two electrons. B) neutral helium atom (atomic number = 2) that has lost no electrons. C) helium molecule that contains two helium atoms. D) helium atom that has lost one electron.

D) helium atom that has lost one electron.

Spectral types of stars (e.g., O, B, A, F, G, K, and M) define uniquely their A) sizes or radii. B) absolute magnitudes. C) luminosities. D) surface temperatures.

D) surface temperatures.

Apparent magnitude is a measure of A) the intrinsic brightness (actual light output) of a star. B) the size (diameter) of a star. C) the temperature of a star. D) the brightness of a star, as seen from the Earth.

D) the brightness of a star, as seen from the Earth.

What fraction of the stars surrounding the Sun are main-sequence stars? A) Almost all of them, about 90% B) There are no main-sequence stars close to the Sun C) Roughly half of them, about 55% D) Very few of them, about 20%

A) Almost all of them, about 90%

Which of the following spectral-luminosity classes corresponds to a red supergiant? A) M2 I B) B7 I C) M3 V D) G2 III

A) M2 I

How many electrons are missing from the ionized silicon atom Si IV? A) Three B) One C) Four D) Five

A) Three

Why are Balmer absorption lines very weak in the spectra of stars with low surface temperatures, significantly below 10,000 K, for example? A) Because the hydrogen atoms have to be hot enough to be ionized in order to show Balmer absorption B) Because there is no emitted continuum radiation at Balmer-line wavelengths when the gas is so cool, so absorption will not be seen C) Because atoms need electrons that have been excited by high-temperature collisions to the n = 2 level in order to undergo Balmer absorption D) Because hydrogen atoms have no electrons in any energy levels at these temperatures

C) Because atoms need electrons that have been excited by high-temperature collisions to the n = 2 level in order to undergo Balmer absorption

Which of the following sequences of stellar spectral classifications is in correct order of increasing temperature? A) K, M, G, F, A, B, O B) A, B, F, G, K, M, O C) M, K, G, F, A, B, O D) O, B, A, F, G, K, M

C) M, K, G, F, A, B, O

How far out into space can we determine stellar distances using telescopes on the Earth if we can only measure stellar parallax values as small as 0.01 arcsec? A) 10 pc B) 100 pc C) 500 pc D) 2000 pc

B) 100 pc

How do astronomers measure the masses of stars? A) By observing the star's brightness at different wavelengths (colors) B) By observing the motion of two stars in a binary star system C) By measuring the star's brightness, temperature, and distance D) By measuring the star's brightness, and obtaining its radius using the H-R diagram

B) By observing the motion of two stars in a binary star system

What is a star's luminosity? A) The amount of energy received per second on one square meter of a planet's surface, exactly 1 AU from the star B) The total energy emitted by the star into all space per second, measured in watts C) The apparent magnitude the star would have if it were located exactly 10 ly from the Earth D) The apparent magnitude the star would have if it were located exactly 10 pc from the Earth

B) The total energy emitted by the star into all space per second, measured in watts

Parallax of a nearby star is used to estimate its A) surface temperature. B) distance from the Earth. C) apparent magnitude. D) physical size or diameter.

B) distance from the Earth.

Stellar parallax is A) the inferred change in the distance to a star as its light is dimmed by passing through an interstellar cloud. B) the apparent shift seen in the position of a nearby star against more distant stars as we orbit the Sun. C) the difference between the apparent and absolute magnitudes of a star. D) the circular or elliptical motion of a star in a binary system as the two stars orbit each other.

B) the apparent shift seen in the position of a nearby star against more distant stars as we orbit the Sun.

An eclipsing binary system consists of A) a star that is periodically eclipsed by the Moon. B) two stars that periodically eclipse each other, as seen from the Earth. C) two stars in which spectral lines move back and forth periodically due to Doppler shift, indicating mutually orbiting stars. D) two mutually orbiting and gravitationally bound stars that are close enough to be resolved when viewed from the Earth.

B) two stars that periodically eclipse each other, as seen from the Earth.