Question 1

How is a luminosity class assigned to a star?

Accepted Answer

The luminosity class of a star is determined by studying the absorption line widths in the spectrum of the star. This allows astronomers to classify the star based on its surface temperature and luminosity, giving it a letter designation from I (supergiant) to V (main sequence).

Question 2

How can we tell that some stars are relatively close to us in the sky?

Accepted Answer

Stars appearing to move back and forth against the background stars due to the Earth's movement around the Sun is called parallax. The closer a star is to us, the greater its parallax, and therefore, we can infer that some stars are relatively close to us if they exhibit noticeable parallax.

Question 3

What is the most reliable way to measure the mass of a star for which the distance is known?

Accepted Answer

Measuring the orbit of a star around another massive object (such as another star or a black hole) using Kepler's laws allows us to calculate its mass, as the mass of the object it is orbiting around can be determined through other means (such as measuring its own orbit). This method is particularly useful for binary star systems or for stars with companions that can be observed. The other methods listed (mass-luminosity and mass-temperature relations, and calculating mass from radius and density) are less reliable as they depend on assumptions about the star's properties and may not be accurate in all cases.

Question 4

What is the most accurate way to determine the surface temperature of a star?

Accepted Answer

The answer of What is the most accurate way to...

Question 5

What property do most of the (apparently)bright stars in the sky share?

Accepted Answer

Most of the apparently bright stars in the sky are very luminous, which is why they appear bright to Earth-based observers.

Question 6

What is the most reliable way to measure the mass of a star for which the distance is unknown?

Accepted Answer

Computing the spectroscopic parallax of a star using its spectral characteristics (luminosity class and surface gravity) and comparing it with its apparent brightness can give an estimate of its distance. Applying the mass-luminosity relation can then provide an estimate of its mass. This method is commonly used for measuring the masses of distant stars.

Question 7

The nearest star,Proxima Centauri,is about four light years away and has a luminosity about 0.001 times that of the Sun.If Proxima Centauri were at a distance of one light year instead of four,how much brighter would it appear in the sky?

Accepted Answer

The answer of The nearest star,Proxima Centauri,is about four light...

Question 8

Define the range of a property as the maximum value divided by the minimum value.Which property of stars has the greatest range?

Accepted Answer

Luminosity is the property of stars that has the greatest range. A star's luminosity can vary from less than a tenth of the Sun's luminosity to millions of times more. In comparison, the mass, radius, and temperature of stars generally have a more limited range.

Question 9

If you took a random sample of 100 main-sequence stars in the Sun's neighbourhood,what would you expect their total mass to be?

Accepted Answer

The answer of If you took a random sample of...

Question 10

The table lists the spectral types for each of four stars.Which star in this table would have the lowest surface temperature?

Accepted Answer

The spectral types in the table go in order of decreasing temperature from O to M. o Cet has the spectral type of M6, which is the furthest down the list in temperature and therefore has the lowest surface temperature compared to the other stars listed.

Question 11

How do humans use their eyes to measure relative distance by parallax?

Accepted Answer

Since our eyes are separated, the brain interprets the relative look angles of the two eyes in terms of distance to the object viewed.

Question 12

Which of the following can we NOT use to determine the surface temperature of a star?

Accepted Answer

Measuring the star's parallax can give us information about its distance from Earth, but not its surface temperature. Studying its continuous spectrum, line absorption spectrum, and measuring its luminosity and diameter can all provide information about its surface temperature.

Question 13

When compared to stars near the middle of the diagram,how are stars in the upper right part of the Hertzsprung-Russell diagram different?

Accepted Answer

Stars in the upper right part of the Hertzsprung-Russell diagram (known as the red giants) are larger than stars near the middle of the diagram. They have exhausted the hydrogen fuel in their cores and have expanded to a larger radius as a result of the nuclear reactions in their outer layers. This expansion causes them to be classified as giant stars.

Question 14

If you compare two stars,which one will always have the greater luminosity?

Accepted Answer

Absolute magnitude is a measure of a star's intrinsic brightness; a smaller absolute magnitude indicates a greater luminosity.

Question 15

Which stars have a large positive absolute magnitude?

Accepted Answer

Stars with a large positive absolute magnitude are those with low luminosity, as absolute magnitude is a measure of a star's intrinsic brightness. A higher positive value indicates a dimmer star.

Question 16

How does a star's surface temperature determine the appearance of its spectrum?

Accepted Answer

The surface temperature of a star affects the velocity of collision rates of atoms and ions, which in turn influences the energy levels and transitions that produce the star's spectral lines.

Question 17

Which star type in the Milky Way is likely to be most completely catalogued?

Accepted Answer

Luminous stars are bright and easy to detect, making them more likely to be catalogued completely.

Question 18

Sirius A and B are two stars at the same distance from the Earth.In this binary system,Sirius A is much brighter but Sirius B is much hotter.From this information,what can you conclude about the two stars?

Accepted Answer

Sirius B is much hotter but less bright, indicating it is smaller in size compared to Sirius A, which is brighter but cooler.

Question 19

What property do most of the nearest stars in the sky share?

Accepted Answer

Most of the nearest stars to Earth are red dwarfs, which are small, cool, and less luminous than the Sun. They are the most common type of star in the Milky Way galaxy.

Question 20

The table lists the spectral types for each of four stars.Which star in this table would have the highest surface temperature?

Accepted Answer

Spectral types are classified from hottest to coolest as O, B, A, F, G, K, M. The star $ \xi $ Per is likely of a spectral type O or B, which are the hottest, indicating it has the highest surface temperature among the options.

Quiz 6: The Family of Stars