Question 1

The Hipparcos mission's data on parallaxes is useful for stellar distances out to about 200 pc.

Accepted Answer

The Hipparcos mission measured parallaxes for over 100,000 stars, and its data is accurate for distances out to about 200 parsecs (over 600 light-years). Beyond that distance, the errors in measurement become too large to provide useful data. The Hipparcos mission's data on parallaxes is useful for stellar distances out to about 200 pc, making option A true.

Question 2

On the main sequence, almost all stars have radii between about 0.1 and 10 times the Sun.

Accepted Answer

This is true. The range of radii on the main sequence is determined by the relationship between a star's radius, mass, and temperature. Most stars on the main sequence have masses between about 0.1 and 10 times the mass of the Sun, and their radii fall within this range as well. This statement is true. The vast majority of stars on the main sequence have radii within this range.

Question 3

First magnitude Spica appears 2.5 times brighter than second magnitude Polaris.

Accepted Answer

Magnitude is a logarithmic measurement of brightness, where a difference of 1 magnitude is equivalent to 2.5 times difference in brightness. Therefore, if Spica is first magnitude and Polaris is second magnitude, Spica is 2.5 times brighter than Polaris. The magnitude scale is logarithmic, meaning each whole number difference represents a difference of 2.5 times in brightness. Therefore, a difference of 1 magnitude corresponds to a brightness ratio of 2.5:1. Since Spica is one magnitude brighter than Polaris, it is 2.5 times brighter.

Question 4

The proper motion of a star, its distance, and Doppler shift can give us its space velocity.

Accepted Answer

The space velocity of a star can be calculated from its proper motion, distance, and Doppler shift. Proper motion tells us how fast the star is moving across the sky, distance gives us its location, and Doppler shift tells us how fast it is moving towards or away from us. Together, these measurements can give us a complete picture of the star's motion through space. The space velocity of a star is determined by its proper motion, distance, and Doppler shift. Proper motion measures the apparent motion of a star relative to the background stars over time, which can be used to calculate its speed and direction of motion. The distance to the star can be determined by various methods, such as parallax or spectroscopic distance measurements. The Doppler shift of the star's spectral lines can reveal its radial velocity relative to Earth, which can be used to calculate its velocity along the line of sight. Together, these measurements can be used to calculate the star's three-dimensional space velocity.

Question 5

About 500 stars can be seen by the naked eye from somewhere on Earth.

Accepted Answer

The actual number of stars visible to the naked eye depends on several factors such as light pollution, weather conditions, and individual eyesight. However, on average, the maximum number of stars visible is around 2,500, not just 500. The actual number of stars visible to the naked eye from Earth varies depending on factors such as location and light pollution, but on average it is around 2,500.

Question 6

Like the Sun, main sequence stars are converting hydrogen into helium in their cores.

Accepted Answer

Main sequence stars, like the Sun, are converting hydrogen into helium through nuclear fusion reactions in their cores. This process releases energy in the form of light and heat, which is what keeps the star stable and shining. Main sequence stars, like the Sun, are actively converting hydrogen into helium through the process of nuclear fusion in their cores. This process releases a tremendous amount of energy and allows the star to maintain its stable state for millions to billions of years.

Question 7

In a binary system, the more massive stars always stay closer to the center of mass and moveslower.

Accepted Answer

This is known as Kepler's Third Law and applies to all binary systems. The more massive star exerts a stronger gravitational pull, causing it to stay closer to the center of mass, while both stars move at the same speed in their orbit. This is known as Kepler's Third Law of Planetary Motion and applies to binary stars as well. The more massive star will have a smaller orbit and move slower around the center of mass, while the less massive star will have a larger orbit and move faster.

Question 8

For luminosity classification, fat stars have skinny spectral lines.

Accepted Answer

Fat stars have a high luminosity, which means they have strong spectral lines because they have a high amount of radiation. Skinny spectral lines are characteristic of stars with low luminosity. Therefore, the statement is true.

Question 9

The vast majority of stars near us would fall to the bottom right on the H-R diagram.

Accepted Answer

This is because most stars near us are main sequence stars, which fall in the bottom right portion of the H-R diagram. The bottom right of the H-R diagram represents cool and dim stars, which make up the majority of stars near us.

Question 10

The proper motion of a star is its true velocity through space.

Accepted Answer

The proper motion of a star refers to its apparent motion across the sky as observed from Earth, not its true velocity through space, which also includes its radial velocity towards or away from us.

Question 11

If a star were moved 10 times farther away, its apparent magnitude would drop by fivemagnitudes.

Accepted Answer

The apparent magnitude of a star follows an inverse square law in relation to distance, meaning if a star is moved 10 times farther away, it would indeed appear 100 times dimmer, which corresponds to a decrease of 5 magnitudes in the astronomical magnitude scale.

Question 12

The nearest naked-eye star to our Sun, Alpha Centauri, is still over a parsec distant.

Accepted Answer

This statement is true. Alpha Centauri is approximately 4.37 light years away from the Sun, which is equivalent to 1.34 parsecs. Alpha Centauri is approximately 1.3 parsecs away from our Sun.

Question 13

The Sun's complete classification is $\text { G2V. }$

Accepted Answer

The Sun is classified as a G2V type star, where "G2" indicates its temperature and color as a yellow dwarf, and "V" (Roman numeral five) denotes it belongs to the main sequence of stars in the Hertzsprung-Russell diagram.

Question 14

If a star were moved 10 times farther away, its absolute magnitude would drop fivemagnitudes.

Accepted Answer

If a star were moved 10 times farther away, its apparent magnitude would drop by 5 magnitudes, not its absolute magnitude. The absolute magnitude of a star depends on its inherent brightness and would not change due to a change in distance. If a star were moved 10 times farther away, its apparent magnitude would drop by 5 magnitudes, but its absolute magnitude would remain the same. Absolute magnitude is a measure of a star's intrinsic brightness, independent of its distance from the observer.

Question 15

A star of the Sun's diameter, but twice as hot, must be 16X more luminous than the Sun.

Accepted Answer

Luminosity is directly proportional to temperature to the fourth power and the radius squared. So, a star with the same radius as the Sun but twice as hot would have a luminosity of (2^4) = 16 times that of the Sun. Luminosity is directly proportional to the fourth power of the star's radius and the square of its temperature. Therefore, a star of the Sun's diameter, but twice as hot, must have a radius of 1 and a temperature of 2, resulting in (1^4)(2^2) = 4 times the Sun's luminosity. Multiplying this by the factor of 4 due to the increase in surface area gives a total of 16 times the Sun's luminosity.

Question 16

In a spectroscopic binary, the star whose lines shift the most weighs the most.

Accepted Answer

In a spectroscopic binary, the star whose spectral lines shift the most actually has the smaller mass. The extent of the Doppler shift in the spectral lines is inversely related to the mass of the star.

Question 17

Hydrogen lines are weaker in both very hot and very cool stars.

Accepted Answer

Hydrogen lines are strongest in stars with temperatures between 5,000K-7,000K. In very hot stars, the hydrogen atoms are fully ionized and there are no electrons available to absorb or emit photons, resulting in weaker lines. In very cool stars, the hydrogen atoms are not excited enough to emit or absorb photons, also resulting in weaker lines.

Question 18

Star A and star B have the same apparent magnitude. Star A is twice as distant as star B.Therefore, star A has twice the luminosity as star B.

Accepted Answer

The statement is incorrect. If star A is twice as distant as star B, then it would have an apparent magnitude that is 2.5 times fainter than that of star B (based on the inverse square law of brightness). Therefore, star A would have only one-fourth the luminosity of star B. The statement is false. According to the inverse square law, the brightness (or luminosity) of a star decreases as the square of the distance increases. Since star A is twice as distant as star B, its brightness would decrease by a factor of 2^2 = 4. Therefore, star A would have only 1/4 the luminosity of star B.

Question 19

A type B9 star is hotter than a type A0.

Accepted Answer

A type B9 star has a higher surface temperature than a type A0 star.

Question 20

Eclipsing binaries are the most useful, giving us sizes as well as masses of the pair.

Accepted Answer

Eclipsing binaries allow us to observe the periodic eclipses of one star by another, which provides us with information on their sizes as well as masses, making them highly useful in astronomy. Eclipsing binaries are useful in determining both the mass and size of the celestial objects involved, making them important tools for astronomers.

Quiz 17: The Stars: Giants, Dwarfs, and the Main Sequence