Question 1

The spectral sequence, in order of decreasing temperature, is

Accepted Answer

The spectral sequence is a classification of stars based on their surface temperature. The letters correspond to the spectral types, with O being the hottest and M being the coolest. The sequence goes from hottest to coolest, so the correct order is OBAFGKM. Choice C is the only option that follows this order.

Question 2

Which of the following correctly states the relationship between the apparent brightness, luminosity, and distance of a star?

Accepted Answer

The relationship between the apparent brightness, luminosity, and distance of a star is given by the inverse square law, which states that the apparent brightness is equal to the luminosity divided by 4π times the distance squared. Therefore, option B correctly states the relationship between the three variables.

Question 3

Which o the following stars are brightest at ultraviolet wavelengths?

Accepted Answer

O and B stars are the hottest and most massive stars, and they emit most of their radiation in ultraviolet wavelengths.

Question 4

On a Hertzsprung-Russell diagram, where would you find stars that are cool and dim?

Accepted Answer

Cool and dim stars are located in the lower right corner of the Hertzsprung-Russell diagram, which plots the brightness of stars against their temperature.

Question 5

What are the standard units for apparent brightness?

Accepted Answer

Apparent brightness is measured in units of power per unit area, specifically watts per square meter (W/m²).

Question 6

You see two main-sequence stars with the same spectral type. Star 1 is dimmer in apparent brightness than Star 2 by a factor of 100. What can you conclude, assuming there is no absorption of either star's light by interstellar gas or dust?

Accepted Answer

The apparent brightness of a star decreases with the square of the distance. If Star 1 is dimmer by a factor of 100, it must be 10 times further away than Star 2, since 10^2 = 100.

Question 7

Which of the following statements about apparent and absolute magnitudes is true?

Accepted Answer

All the statements accurately describe aspects of the magnitude system used in astronomy.

Question 8

You measure the parallax angle for a star to be 0.5 arcseconds. The distance to this star is

Accepted Answer

The distance to a star in parsecs is the reciprocal of the parallax angle in arcseconds. Therefore, a parallax angle of 0.5 arcseconds corresponds to a distance of 1/0.5 = 2 parsecs.

Question 9

What are the standard units for luminosity?

Accepted Answer

The standard unit for luminosity is the watt (W), which measures the amount of energy emitted per second.

Question 10

Which of the following statements about spectral types of stars is true?

Accepted Answer

Each statement is true regarding the spectral types of stars. Spectral type indicates a star's surface temperature, which in turn determines its color. The sequence from hottest to coolest is O, B, A, F, G, K, M, so an A-type star is cooler than a B-type star. Within a given spectral class, lower numbers indicate hotter stars, so an F2 star is hotter than an F3 star.

Question 11

A star's luminosity is the

Accepted Answer

A star's luminosity is the total amount of energy that the star radiates each second. Options A and B refer to the star's apparent brightness and surface temperature, respectively, which are not the same as luminosity. Option C refers to the lifetime of the star, which is not directly related to its luminosity. Option D is tempting because it refers to the total amount of energy radiated, but it specifies over the star's entire lifetime rather than per second.

Question 12

The spectral sequence sorts stars according to

Accepted Answer

The spectral sequence, also known as the Harvard spectral classification scheme, sorts stars based on their surface temperature, with the hottest stars being classified as O and the coolest as M. This system is based on the absorption lines in the stars' spectra, which vary with temperature. A star's temperature is a fundamental characteristic that helps to determine other properties such as mass, luminosity, and radius.

Question 13

Which stellar spectral type has strong molecular absorption lines in its optical spectrum?

Accepted Answer

M-type stars have cooler temperatures, allowing molecules to form and produce strong molecular absorption lines in their optical spectra.

Question 14

The most distant stars we can measure stellar parallax for are approximately

Accepted Answer

Stellar parallax is the apparent shift in the position of a star due to the Earth's orbit around the Sun. This effect is used to measure the distance to nearby stars within our Milky Way Galaxy. The precision of the measurement depends on the size of the baseline, which is the distance between the Earth at two different times of the year. The maximum baseline we can achieve on Earth is approximately 300 million km, which corresponds to a maximum distance of about 100 parsecs (~ 330 light-years). Therefore, choice B is correct as the most distant stars we can measure stellar parallax for are about 100 parsecs away. The other choices are incorrect as they are much farther away than what we can measure with parallax.

Question 15

You measure the parallax angle for a star to be 0.1 arcseconds. The distance to this star is

Accepted Answer

The distance to a star in parsecs is the inverse of the parallax angle in arcseconds. Therefore, a parallax angle of 0.1 arcseconds corresponds to a distance of 10 parsecs (1/0.1 = 10).

Question 16

Since all stars begin their lives with the same basic composition, what characteristic most determines how they will differ?

Accepted Answer

The mass they are formed with is the most determining characteristic in how stars will differ. The initial mass of the star determines the temperature, luminosity, and evolutionary path it follows.

Question 17

Which of the following terms is given to a pair of stars that appear to change position in the sky, indicating that they are orbiting one another?

Accepted Answer

A visual binary is a pair of stars that can be individually resolved through a telescope and appear to change position relative to each other, indicating they are orbiting one another.

Question 18

Which of the following best describes the axes of a Hertzsprung-Russell (H-R) diagram?

Accepted Answer

In a Hertzsprung-Russell (H-R) diagram, the horizontal axis shows surface temperature (or spectral class) and the vertical axis shows luminosity (or absolute magnitude). This arrangement allows astronomers to see the relationship between a star's temperature and its brightness, providing insight into its size, age, and evolutionary stage.

Question 19

If the distance between us and a star is doubled, with everything else remaining the same, its luminosity

Accepted Answer

Luminosity is an intrinsic property of a star and does not change with distance. Apparent brightness decreases with the square of the distance, so doubling the distance decreases the apparent brightness by a factor of four.

Question 20

The faintest star visible to the naked eye has an apparent magnitude of about

Accepted Answer

The apparent magnitude scale is a logarithmic scale that ranges from -26 to +6, with smaller numbers indicating brighter objects. The faintest star visible to the naked eye has an apparent magnitude of about 6. Therefore, the best choice is B.

Quiz 11: Surveying the Stars