Chapter 15
A star of spectral type G lives approximately how long on the main sequence?
10 billion years
A star of spectral type O lives approximately how long on the main sequence?
10 million years
Suppose you measure the parallax angle for a particular star to be 0.1 arc second. The distance to this star is
10 parsecs.
Suppose that you measure the parallax angle for a particular star to be 0.5 arcsecond. The distance to this star is
2 parsecs.
A star with a parallax angle of 1/20 arcsecond is.
20 parsecs away.
Ten parsecs is about
32.6 light-years You find this by remembering that 1 parsec = 3.26 light-years.
The most distance stars we can measure stellar parallax for are approximately
500 parsecs away.
The faintest star visible to the naked eye has an apparent magnitude of about
6.
Which of the following statements about an open cluster is true?
All stars in the cluster are approximately the same age
Which of the following is the most common type of main-sequence star?
An M star.
Which of the following persons reorganized the spectral classification scheme into the one we use today and personally classified over 400,00 stars?
Annie Jump Cannon
Which of the following persons used the ideas of quantum mechanics to describe why the spectral classification scheme is in order of decreasing temperature?
Cecilia Payne-Gaposchkin
Suppose our Sun were suddenly replaced by a supergiant star. Which of the following would be true?
Earth would be inside the supergiant
The apparent brightness of a star depends only on its luminosity.
False
In order to understand star clusters, we need to be able to estimate their ages. What technique do scientists use for this?
Finding the main-sequence turnoff point of the stars
Our Sun is a star of spectral type
G
Why do astronomers often measure the visible-light apparent brightness instead of the total apparent brightness of a star?
In order to measure the total apparent brightness of a star, you must measure its brightness in all wavelengths, and this is difficult to do. The only wavelengths you can measure from the surface of the Earth are visible and radio wavelengths.
According to the inverse square law of light, how will the apparent brightness of an object change if its distance to us triples?
Its apparent brightness will decrease by a factor of 9
All stars are born with the same basic composition, yet stars can look quite different from one another. Which two factors primarily determine the characteristics of a star?
Its mass and its stage of life
Which of the following is true about low-mass stars compared to high-mass stars?
Low-mass stars are cooler and less luminous than high-mass stars
On a Hertzsprung-Russel diagram, where would we find white dwarfs?
Lower left
On a Hertzsprung-Russel diagram, where would we fine stars that are cool and dim?
Lower right
In a pulsating variable star, which characteristic of the star changes dramatically with time?
Luminosity
Which of the following characteristics of stars has the greatest range in values?
Luminosity
Since all stars begin their lives with the same basic composition, what characteristic most determines how they will differ?
Mass they are formed with
Which of the following statements about a global cluster is true?
Most stars in the cluster are yellow or reddish in color
The spectral sequence in order of decreasing temperature is
OBAFGKM
Which of the following terms is given to a pair of stars that we can determine are orbiting each other only by measuring their periodic Doppler shifts?
Spectroscopic binary
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.)
Star 1 is 10 times more distant than Star 2
Which of the following best describes the axes of a Hertzsprung-Russel (H-R) diagram?
Surface temperature on the horizontal axis and luminosity on the vertical axis
Which of the following statements about apparent and absolute magnitudes is true?
The magnitude system that we use now is based on a system used by the ancient Greeks over 2,000 years ago that classified stars by how bright they appeared. A star with apparent magnitude 1 is brighter than one with apparent magnitude 2. The absolute magnitude of a star is another measure of its luminosity. A star's absolute magnitude is the apparent magnitude it would have if it were at a distance of 10 parsecs from Earth. (All of the above are true)
Why is the spectral sequence of stars not alphabetical?
The original alphabetical labeling did not correspond to surface temperature and this had to be reordered
Which of the following statements about spectral types of stars is true?
The spectral type of a star can be used to determine its surface temperature. The spectral type of a star can be used to determine its color. A star with spectral type A is cooler than a star with spectral type B. A star with spectral type F2 is hotter than a star with spectral type F3. (All of the above are true.)
Why are Cepheid variable so important for measuring distances in astronomy?
Their luminosity can be inferred from their period
Approximately, what basic composition are all stars born with?
Three-quarters hydrogen, one-quarter helium, no more than two percent heavier elements.
On a Hertzsprung-Russel diagram, where on the main sequence would we find stars that have the greatest mass?
Upper left
On a Hertzsprung-Russel diagram, where would we find red giant stars?
Upper right
On a Hertzsprung-Russel diagram, where would we find stars that are cool and luminous?
Upper right
On a Hertzsprung-Russel diagram, where would we find stars that have the largest radii?
Upper right
Which of the following luminosity classes refers to stars on the main sequence?
V
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?
Visual binary
What are the standard units for luminosity?
Watts
What are the standard units for apparent brightness?
Watts per square meter
Which of the following correctly states the luminosity-distance formula?
apparent brightness=luminosity/4pi*(distance)^2
One the main sequence, stars orbit their energy
by converting hydrogen to helium.
Cluster ages can be determined from
main sequence turnoff
If the distance between us and a star is doubled, with everything else remaining the same, the luminosity
remains the same, but the apparent brightness is decreased by a factor of four
You observe a star in the disk of the Milky Way, and you want to plot the star on an H-R diagram. You will need to determine all of the following, except the
rotation rate of the star.
The spectral sequence sorts stars according to
surface temperature.
A star's luminosity is the
total amount of light that the star radiates each second
