Question 1

Two stars in our sky have the same apparent brightness.If neither of them is hidden behind gas or dust clouds,then we know that they:

Accepted Answer

If two stars have the same apparent brightness but are at different distances, the farther star must have greater luminosity to appear as bright as the nearer one.

Question 2

How bright (in absolute magnitude)are the intrinsically faintest stars in the universe?

Accepted Answer

The intrinsically faintest stars in the universe have an absolute magnitude of around +17, making them very difficult to observe without powerful telescopes.

Question 3

Three stars have the following apparent (m)and absolute (M)magnitudes: Star A: M = 1.8 m = 3.8
Star B: M = 2.5 m = 9.5
Star C: M = 7.6 m = 15.1
Which star is farthest away?

Accepted Answer

The answer of Three stars have the following apparent (m)and...

Question 4

The star Arietis has an apparent magnitude of +2.7 and a distance of 52 ly.According to the equation in Discovery 10-2 in Comins,Discovering the Essential Universe,6th ed.,what is its absolute magnitude?

Accepted Answer

The absolute magnitude (M) can be calculated using the formula: M = m - 5(log10(d) - 1), where m is the apparent magnitude and d is the distance in parsecs. First, convert the distance from light-years to parsecs: 52 ly ≈ 15.9 pc. Then, M = 2.7 - 5(log10(15.9) - 1) ≈ 1.7.

Question 5

A particular star is at a distance of 5 pc from Earth.For this star,the apparent magnitude will have:

Accepted Answer

Apparent magnitude is affected by the distance of the star from Earth, so a star at a distance of 5 pc will have a smaller apparent magnitude than its absolute magnitude.

Question 6

A particular star is at a distance of 20 pc from Earth.For this star,the apparent magnitude will have:

Accepted Answer

The apparent magnitude of a star becomes larger (dimmer) as the distance increases, while the absolute magnitude is a measure of its intrinsic brightness at a standard distance of 10 parsecs. Since this star is at 20 parsecs, its apparent magnitude will be larger (indicating it appears dimmer) than its absolute magnitude.

Question 7

The luminosity of a star is:

Accepted Answer

Luminosity refers to the total amount of energy a star emits into space, regardless of its distance from Earth or how bright it appears to us. It is measured in units of watts or solar luminosities.

Question 8

The star Alderamin has an apparent magnitude of 2.4 and an absolute magnitude of 1.4.The star Merak has an apparent magnitude of 2.4 and absolute magnitude of 0.5.Assuming that neither star has been dimmed by interstellar clouds,we can say for sure that Merek is:

Accepted Answer

Both stars have the same apparent magnitude of 2.4, but Merak has a brighter absolute magnitude of 0.5 compared to Alderamin's absolute magnitude of 1.4. This means that Merak is intrinsically brighter than Alderamin. However, both stars have the same apparent magnitude, which is simply a measure of how bright they appear from Earth. Therefore, the only possible explanation for this is that Merak is farther away from Earth than Alderamin, which would cause it to appear equally as bright despite being intrinsically brighter.

Question 9

The luminosity of a star is a unique measure of its:

Accepted Answer

Luminosity is a measure of the total energy output of a star, taking into account both its brightness and distance from us. It is independent of the star's velocity of recession, temperature, and physical size.

Question 10

A star whose absolute magnitude M is +2.2 is seen to have an apparent magnitude when viewed from Earth of +5.2.According to the equation in Discovery 10-2 in Comins,Discovering the Essential Universe,6th ed.,how far away is the star?

Accepted Answer

The answer of A star whose absolute magnitude M is...

Question 11

A star that is 100 pc distant from Earth has an apparent magnitude of m +2.5.According to the equation in Discovery 10-2 in Comins,Discovering the Essential Universe,6th ed.,what is its absolute magnitude?

Accepted Answer

The absolute magnitude (M) can be calculated using the distance modulus formula: M = m - 5(log10(d) - 1), where m is the apparent magnitude and d is the distance in parsecs. For a star 100 pc away with m = +2.5, M = 2.5 - 5(log10(100) - 1) = 2.5 - 5(2 - 1) = 2.5 - 5 = -2.5.

Question 12

A particular star has an apparent magnitude of +12 and an absolute magnitude of +5.According to the equation in Discovery 10-2 in Comins,Discovering the Essential Universe,6th ed.,what is the distance to this star?

Accepted Answer

The answer of A particular star has an apparent magnitude...

Question 13

The star Fomalhaut has an apparent magnitude of 1.15 and an absolute magnitude of 2.0.From this information (assuming that the starlight has not been dimmed by interstellar clouds),we can say for sure that Fomalhaut is _____ away.

Accepted Answer

The answer of The star Fomalhaut has an apparent magnitude...

Question 14

A star is at such a distance that its apparent magnitude (m)is 10 magnitudes fainter than its absolute magnitude (M).How far away is it?

Accepted Answer

The distance modulus equation is m-M=5log(d/10), where d is the distance in parsecs. By substituting m=M+10, we get 10=5log(d/10), which simplifies to log(d/10)=2. Solving for d, we get d=1000 pc.

Question 15

The Sun's absolute magnitude is about +5.The brightest stars in our sky have absolute magnitudes of about -10.What is the luminosity of these stars compared with that of the Sun,assuming that they have similar spectral light distributions?

Accepted Answer

Absolute magnitude is a measure of the intrinsic brightness of a star, meaning its luminosity at a standard distance of 10 parsecs (32.6 light-years). The difference between the absolute magnitude of the Sun (+5) and that of the brightest stars in our sky (-10) is 15 magnitudes. Each magnitude corresponds to a factor of 2.5 in brightness, so the difference in brightness between the two is 2.5 to the power of 15, which is approximately 1 million. Therefore, the luminosity of these stars is about 1 million times greater than that of the Sun.

Question 16

What is a star's luminosity?

Accepted Answer

Luminosity refers to the total amount of electromagnetic energy emitted by a star into space per unit time, usually measured in watts. Option A refers to the solar constant, which is the amount of energy received per second on 1 m² of a planet's surface exactly 1 AU from the star. Options C and D are incorrect as apparent magnitude depends on both the luminosity of the star and its distance from Earth.

Question 17

The star Alderamin has an apparent magnitude of 2.4 and an absolute magnitude of 1.4.From this information (assuming that the starlight has not been dimmed by interstellar clouds),we can say for sure that Alderamin is _____ away.

Accepted Answer

The distance modulus formula relates apparent magnitude, absolute magnitude, and distance in parsecs. Since Alderamin's apparent magnitude is greater than its absolute magnitude, it must be more than 10 parsecs away.

Question 18

The star β Phoenicis has an apparent magnitude of +3.4 and an absolute magnitude of -4.6.The North Star (Polaris)has an apparent magnitude of +2.0 and an absolute magnitude of -4.6.Assuming that no light has been absorbed or scattered by interstellar dust,we can say for sure that Polaris is:

Accepted Answer

Both stars have the same absolute magnitude of -4.6, which means they have the same intrinsic brightness. However, Polaris has a greater apparent magnitude of +2.0, which means it appears brighter in the sky. Since apparent magnitude is affected by distance, we can conclude that Polaris must be closer to Earth than β Phoenicis, which has an apparent magnitude of +3.4. Therefore, option B is the best choice.

Question 19

How bright (in absolute magnitude)are the intrinsically brightest stars in the universe?

Accepted Answer

The intrinsically brightest stars in the universe are supernovae, which can have absolute magnitudes as bright as -10.

Question 20

Three stars have the following apparent (m)and absolute (M)magnitudes: Star A: M = 1.8 m = 3.8
Star B: M = 2.5 m = 9.5
Star C: M = 7.6 m = 15.1
Which star is closest?

Accepted Answer

The closer a star is to us, the brighter it appears in the sky. This means that the star with the smallest apparent magnitude (m) is the closest. In this case, Star A has the smallest apparent magnitude (m = 3.8) and therefore is closest.

Quiz 10: Characterizing Stars

Two stars in our sky have the same apparent brightness.If neither of them is hidden behind gas or dust clouds,then we know that they:

How bright (in absolute magnitude) are the intrinsically faintest stars in the universe?

Three stars have the following apparent (m) and absolute (M) magnitudes: Star A: M = 1.8 m = 3.8 Star B: M = 2.5 m = 9.5 Star C: M = 7.6 m = 15.1 Which star is farthest away?

The star Arietis has an apparent magnitude of +2.7 and a distance of 52 ly.According to the equation in Discovery 10-2 in Comins,Discovering the Essential Universe,6th ed.,what is its absolute magnitude?

A particular star is at a distance of 5 pc from Earth.For this star,the apparent magnitude will have:

A particular star is at a distance of 20 pc from Earth.For this star,the apparent magnitude will have:

The luminosity of a star is:

The star Alderamin has an apparent magnitude of 2.4 and an absolute magnitude of 1.4.The star Merak has an apparent magnitude of 2.4 and absolute magnitude of 0.5.Assuming that neither star has been dimmed by interstellar clouds,we can say for sure that Merek is:

The luminosity of a star is a unique measure of its:

A star whose absolute magnitude M is +2.2 is seen to have an apparent magnitude when viewed from Earth of +5.2.According to the equation in Discovery 10-2 in Comins,Discovering the Essential Universe,6th ed.,how far away is the star?

A star that is 100 pc distant from Earth has an apparent magnitude of m +2.5.According to the equation in Discovery 10-2 in Comins,Discovering the Essential Universe,6th ed.,what is its absolute magnitude?

A particular star has an apparent magnitude of +12 and an absolute magnitude of +5.According to the equation in Discovery 10-2 in Comins,Discovering the Essential Universe,6th ed.,what is the distance to this star?

The star Fomalhaut has an apparent magnitude of 1.15 and an absolute magnitude of 2.0.From this information (assuming that the starlight has not been dimmed by interstellar clouds) ,we can say for sure that Fomalhaut is _____ away.

A star is at such a distance that its apparent magnitude (m) is 10 magnitudes fainter than its absolute magnitude (M) .How far away is it?

The Sun's absolute magnitude is about +5.The brightest stars in our sky have absolute magnitudes of about -10.What is the luminosity of these stars compared with that of the Sun,assuming that they have similar spectral light distributions?

What is a star's luminosity?

The star Alderamin has an apparent magnitude of 2.4 and an absolute magnitude of 1.4.From this information (assuming that the starlight has not been dimmed by interstellar clouds) ,we can say for sure that Alderamin is _____ away.

The star β Phoenicis has an apparent magnitude of +3.4 and an absolute magnitude of -4.6.The North Star (Polaris) has an apparent magnitude of +2.0 and an absolute magnitude of -4.6.Assuming that no light has been absorbed or scattered by interstellar dust,we can say for sure that Polaris is:

How bright (in absolute magnitude) are the intrinsically brightest stars in the universe?

Three stars have the following apparent (m) and absolute (M) magnitudes: Star A: M = 1.8 m = 3.8 Star B: M = 2.5 m = 9.5 Star C: M = 7.6 m = 15.1 Which star is closest?