Question 1

Which of the following combinations of measurements CANNOT be used to determine a star's radius?
A) brightness and peak wavelength
B) angular size and distance
C) brightness, distance, and temperature
D) luminosity and peak wavelength

Accepted Answer

Brightness and peak wavelength can only be used to determine a star's temperature, not its radius. To determine a star's radius, you need at least two measurements such as angular size and distance, or luminosity and temperature.

Question 2

What property of a star's spectral lines allows astronomers to measure stellar masses?
A) depth
B) width
C) wavelength
D) spacing

Accepted Answer

The width of a star's spectral lines indicates the velocity at which the gas in the star is moving. By measuring the width and shape of spectral lines, astronomers can determine the mass of the star through a process called Doppler broadening. This is because the velocity of a star is related to its mass through the gravitational force that holds it together.

Question 3

Why are stars considered to be thermodynamic systems?
A) Stars are hot.
B) Stars are always in motion.
C) Stars are giant collections of atoms.
D) Stars are powered by combustion.

Accepted Answer

Stars are considered thermodynamic systems because they are giant collections of atoms that undergo nuclear fusion, releasing energy and maintaining a balance of pressure and temperature.

Question 4

What property of a star can best be used to determine its temperature?
A) luminosity
B) color
C) brightness
D) velocity

Accepted Answer

The color of a star is directly related to its temperature. For example, hotter stars will appear bluer in color while cooler stars will appear more orange or red. Therefore, observing a star's color can provide valuable information about its temperature.

Question 5

Star A's spectrum is most intense at 500 nm,while star B's spectrum is most intense at 750 nm.If star A has a temperature of 5,800 K,what is the temperature of star B?
A) 13,000 K
B) 8,700 K
C) 4,500 K
D) 3,850 K

Accepted Answer

According to Wien's Law, the peak wavelength is inversely proportional to the temperature. If star A's peak is at 500 nm with a temperature of 5,800 K, then star B's peak at 750 nm will have a lower temperature. Using Wien's Law, T = (2.898 x 10^6 nm*K) / wavelength, star B's temperature is approximately 3,850 K.

Question 6

How would astronomers measure the velocity of the star shown in the figure below? 
A) through its spectrum
B) through a transit
C) through its angular velocity across the sky
D) through its brightening or dimming with time

Accepted Answer

Astronomers would measure the velocity of the star shown in the figure through its spectrum. This can be done by analyzing the Doppler shift of the star's spectral lines, which will reveal whether the star is moving towards or away from Earth and at what speed.

Question 7

If star A has an apparent magnitude of 8 while star B has an apparent magnitude of 13,then star A is ________ than star B.
A) 100 times fainter
B) 5 times fainter
C) 5 times brighter
D) 100 times brighter

Accepted Answer

The magnitude scale is logarithmic, meaning that every increase of 1 in magnitude corresponds to a decrease in brightness by a factor of approximately 2.512 (the actual value is 2.512^(1/5)). Thus, the difference in magnitude between star A and star B is 13-8=5, corresponding to a difference in brightness by a factor of 2.512^5, or approximately 100. Since star A has the smaller magnitude (i.e. it is brighter), it must be 100 times brighter than star B. Therefore, the answer is D) 100 times brighter.

Question 8

What properties of Cepheid variable stars are most often measured to determine their distance?
A) luminosity and brightness
B) period and brightness
C) luminosity and temperature
D) period and temperature

Accepted Answer

The period and brightness of Cepheid variable stars are most often measured to determine their distance. The period-luminosity relationship of Cepheids allows astronomers to calculate their intrinsic luminosity, which can then be compared with their apparent brightness to determine their distance.

Question 9

How have astronomers learned about the life cycles of stars?
A) through laboratory experiments
B) by studying the Big Bang
C) by studying the complete life cycles of individual stars
D) by measuring the properties of many stars at a single instant

Accepted Answer

Astronomers learn about the life cycles of stars by observing and measuring the properties of a vast number of stars at various stages of their life cycles at a single instant. Since stars exist for millions to billions of years, it's not feasible to observe the complete life cycle of a single star. Instead, by studying many stars at different stages of their evolution, astronomers can piece together the general life cycle of stars.

Question 10

What was Henrietta Leavitt's most important contribution to astronomy?
A) the spectral typing of stars
B) the relationship of stellar spectral type to temperature
C) the period-luminosity relation of Cepheid variables
D) the discovery of interstellar reddening

Accepted Answer

Henrietta Leavitt's most significant contribution to astronomy was discovering the relationship between the period and luminosity of Cepheid variables. This allowed astronomers to determine the distance to other galaxies and led to the development of the cosmic distance ladder.

Question 11

Two stars orbit each other on circular orbits.The star with the larger orbital radius has a:
A) larger orbital period.
B) smaller mass.
C) smaller orbital speed.
D) smaller orbital period.

Accepted Answer

The answer of Two stars orbit each other on circular...

Question 12

A star has a parallax of 0.05 arcseconds.How far away from Earth is the star?
A) 20 parsecs
B) 5 parsecs
C) 0.5 parsecs
D) 0.05 parsecs

Accepted Answer

The distance in parsecs can be calculated as the reciprocal of the parallax angle in arcseconds, so 1/0.05 = 20 parsecs.

Question 13

What property of a star's spectral lines allows astronomers to measure stellar masses?
A) redshift
B) width
C) variability
D) depth

Accepted Answer

The width of a star's spectral lines can indicate its mass because broader lines are typically associated with more massive stars. This is due to the effects of gravitational broadening, where the star's strong gravity affects the energy levels of its atoms, leading to broader spectral lines.

Question 14

Star A has an apparent magnitude of 7,while star B has an apparent magnitude of 12.If star A is four times more luminous than star B,how do the distances of the two stars compare?
A) Star A is 25 times farther than star B.
B) Star A is 5 times farther than star B.
C) Star A is 25 times closer than star B.
D) Star A is 5 times closer than star B.

Accepted Answer

The answer of Star A has an apparent magnitude of...

Question 15

What quantities must be measured in order to calculate the luminosity of a star?
A) brightness and radius
B) radius and distance
C) temperature and distance
D) brightness and distance

Accepted Answer

The luminosity of a star can be calculated by measuring the star's brightness (usually in terms of magnitude or flux) and its distance from Earth. The radius and temperature of the star can be used to calculate other properties such as its surface area and temperature, but they are not directly needed to determine its luminosity.

Question 16

Which of the following must be measured in order to determine a star's proper motion?
A) angular position at multiple times
B) mass
C) redshift or blueshift
D) radius

Accepted Answer

Proper motion is the apparent motion of a star in the sky over time due to its actual motion through space. To determine this, the angular position of the star must be measured at multiple times and compared to determine its motion. Mass, radius, and redshift or blueshift are not directly related to a star's proper motion.

Question 17

Stars A and B have equal brightness,but star B is eight times as far from Earth as star A.How much more luminous is star A than star B?
A) 1/64
B) 1/8
C) 8
D) 64

Accepted Answer

The answer of Stars A and B have equal brightness,but...

Question 18

Two stars orbit their common center of mass on circular orbits.Star A is four times more massive than star B.How do their orbital periods compare to each other?
A) Star A has a longer orbital period than star B.
B) Star B has a longer orbital period than star A.
C) They are the same.
D) The orbital periods cannot be determined without knowing their initial velocities.

Accepted Answer

The orbital period is directly proportional to the radius of the orbit, and inversely proportional to the square root of the mass of the star. Since star A is four times more massive than star B, its radius must be two times smaller than the radius of star B's orbit, so that both stars can have the same center of mass. Therefore, using Kepler's third law, their orbital periods must be the same.

Question 19

The Hubble Space Telescope has detected galaxies with apparent magnitudes of about 30.Approximately how much fainter are these galaxies than stars with an apparent magnitude of 5? A) 10²⁵ times B) 10¹⁰ times C) 2,500 times D) 25 times

Accepted Answer

The difference in brightness between two objects with apparent magnitudes m1 and m2 is given by the equation:
m2 - m1 = 2.5 log (F1/F2)
where F1 and F2 are the fluxes (amount of light) emitted by the objects.
If we assume that the galaxies detected by Hubble have an apparent magnitude of 30, and we want to compare them to stars with an apparent magnitude of 5, we can set m1 = 30 and m2 = 5 in the equation above:
5 - 30 = 2.5 log (Fgalaxies/Fstar)
-25 = 2.5 log (Fgalaxies/Fstar)
-25/2.5 = log (Fgalaxies/Fstar)
-10 = log (Fgalaxies/Fstar)
10^-10 = Fgalaxies/Fstar
This means that the flux emitted by the galaxies detected by Hubble is about 10 billion times fainter than the flux emitted by stars with an apparent magnitude of 5.
10 billion can be written as 10^1.1, which is approximately equal to 10^1. Therefore, the galaxies are about 10^1 or 10 times fainter than stars with an apparent magnitude of 5. Choice B is the closest option.

Question 20

Which of the following is a relational property of stars?
A) radius
B) temperature
C) luminosity
D) distance

Accepted Answer

Distance is a relational property because it describes a star's position relative to other objects, rather than an intrinsic property of the star itself like radius, temperature, or luminosity.

Quiz 11: Measuring the Stars: the Main Sequence and Its Meaning

Which of the following combinations of measurements CANNOT be used to determine a star's radius?

What property of a star's spectral lines allows astronomers to measure stellar masses?

Why are stars considered to be thermodynamic systems?

What property of a star can best be used to determine its temperature?

Star A's spectrum is most intense at 500 nm,while star B's spectrum is most intense at 750 nm.If star A has a temperature of 5,800 K,what is the temperature of star B?

How would astronomers measure the velocity of the star shown in the figure below?

If star A has an apparent magnitude of 8 while star B has an apparent magnitude of 13,then star A is ________ than star B.

What properties of Cepheid variable stars are most often measured to determine their distance?

How have astronomers learned about the life cycles of stars?

What was Henrietta Leavitt's most important contribution to astronomy?

Two stars orbit each other on circular orbits.The star with the larger orbital radius has a:

A star has a parallax of 0.05 arcseconds.How far away from Earth is the star?

What property of a star's spectral lines allows astronomers to measure stellar masses?

Star A has an apparent magnitude of 7,while star B has an apparent magnitude of 12.If star A is four times more luminous than star B,how do the distances of the two stars compare?

What quantities must be measured in order to calculate the luminosity of a star?

Which of the following must be measured in order to determine a star's proper motion?

Stars A and B have equal brightness,but star B is eight times as far from Earth as star A.How much more luminous is star A than star B?

Two stars orbit their common center of mass on circular orbits.Star A is four times more massive than star B.How do their orbital periods compare to each other?

The Hubble Space Telescope has detected galaxies with apparent magnitudes of about 30.Approximately how much fainter are these galaxies than stars with an apparent magnitude of 5?

Which of the following is a relational property of stars?