Question 1

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

Accepted Answer

Visual binary stars are pairs of stars that can be directly observed through a telescope as they orbit each other, appearing to change positions in the sky relative to each other.

Question 2

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

Accepted Answer

The most distant stars we can currently measure stellar parallax for are approximately 500 parsecs away. This is because parallax measurements become more difficult as the distance to the star increases, and beyond a certain point (around 500 parsecs), the parallax becomes too small to reliably measure with current technology.

Question 3

Suppose that you measure the parallax angle for a particular star to be 0.5 arcsecond.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, 1/0.5 = 2 parsecs.

Question 4

Approximately,what basic composition are all stars born with?

Accepted Answer

The basic composition of stars is approximately three-quarters hydrogen and one-quarter helium, with no more than 2 percent heavier elements. This is known as the "metallicity" of the star, which can affect its lifespan, temperature, and other characteristics.

Question 5

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 6

Which of the following persons used the ideas of quantum mechanics to describe why the spectral classification scheme is in order of decreasing temperature?

Accepted Answer

Cecilia Payne-Gaposchkin used the ideas of quantum mechanics to explain why hotter stars have ionized elements in their spectra while cooler stars have more neutral elements. This led to the development of the spectral classification scheme, which orders stars by temperature. Annie Jump Cannon, Williamina Fleming, Henry Draper, and Edward Pickering all made significant contributions to the classification of stars based on their spectra, but did not directly apply quantum mechanics to this problem.

Question 7

The spectral sequence sorts stars according to

Accepted Answer

The spectral sequence (O, B, A, F, G, K, M) sorts stars based on their surface temperature, with O being the hottest and M being the coolest.

Question 8

Which of the following persons reorganized the spectral classification scheme into the one we use today and personally classified over 400,000 stars?

Accepted Answer

Annie Jump Cannon reorganized the spectral classification scheme and personally classified over 400,000 stars using the system, which is still in use today.

Question 9

Suppose you measure the parallax angle for a particular star to be 0.1 arcsecond.The distance to this star is

Accepted Answer

Parallax angle is inversely proportional to the distance of the star. The formula for calculating distance using parallax angle is Distance (in parsecs) = 1/Parallax Angle (in arcseconds).

Using this formula, Distance = 1/0.1 = 10 parsecs. Therefore, the answer is choice B: 10 parsecs.

Question 10

Which of the following correctly states the luminosity-distance formula?

Accepted Answer

The answer of Which of the following correctly states the...

Question 11

Why is the spectral sequence of stars not alphabetical?

Accepted Answer

The original alphabetical labeling of star spectral sequences did not correspond to surface temperature and had to be reordered to reflect the increasing temperature of stars.

Question 12

The spectral sequence in order of decreasing temperature is

Accepted Answer

The spectral sequence in order of decreasing temperature is OBAFGKM. This sequence is based on the temperature classification system, where stars are classified from hottest to coldest based on their spectral lines. The sequence starts with O-stars (hottest) followed by B, A, F, G, K, and M-stars (coldest).

Question 13

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 characteristic that most determines how stars will differ. This is because a star's mass determines its temperature, luminosity, size, and lifespan. Higher mass stars burn their fuel faster and have shorter lifespans, while lower mass stars have cooler temperatures and longer lifespans.

Question 14

Why do astronomers often measure the visible-light apparent brightness instead of the total apparent brightness of a star?

Accepted Answer

In order to accurately measure the total apparent brightness of a star, it's necessary to account for all wavelengths of light it emits. However, this is challenging because not all wavelengths can be easily detected from Earth's surface; we are primarily limited to visible and radio wavelengths. This limitation makes measuring the total apparent brightness difficult, hence the focus on visible-light apparent brightness.

Question 15

Suppose you see two main-sequence stars of the same spectral type.Star 1 is dimmer in apparent brightness than Star 2 by a factor of 100.What can you conclude? (Neglect any effects that might be caused by interstellar dust and gas. )

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 is 10 times farther away than Star 2.

Question 16

A star's luminosity is the

Accepted Answer

Luminosity refers to the total amount of energy (light) a star emits per second. It is a measure of the star's intrinsic brightness, regardless of its distance from us.

Question 17

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

Accepted Answer

Each statement accurately describes aspects of the magnitude system and the concepts of apparent and absolute magnitudes. Statement A outlines the historical basis of the magnitude system. Statement B explains the scale of apparent magnitudes, where a lower number indicates a brighter star. Statement C and D correctly describe absolute magnitude as a measure of a star's intrinsic brightness and its hypothetical apparent brightness at a standard distance of 10 parsecs, respectively.

Question 18

What are the standard units for apparent brightness?

Accepted Answer

The standard units for apparent brightness are watts per square meter. This unit measures the amount of energy emitted by a celestial body per unit area as seen from Earth. It takes into account both the intrinsic brightness of the object and its distance from us. The other choices – watts, joules, Newtons, and watts per second – do not measure apparent brightness.

Question 19

What are the standard units for luminosity?

Accepted Answer

The standard unit for luminosity is watts. This unit measures the amount of energy emitted by an object per unit time, specifically the rate at which a star emits energy into space.

Question 20

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

Accepted Answer

Luminosity, which is the total amount of energy a star emits per unit of time, does not change with distance. However, apparent brightness decreases with the square of the distance, so doubling the distance results in a decrease by a factor of four.

Quiz 15: Surveying the Stars