Approximately what basic composition are all stars born with? |
three-quarters hydrogen, one-quarter helium, no more than 2 percent heavier elements |
Since all stars begin their lives with the same basic composition, what characteristic most determines how they will differ? |
mass they are formed with |
What are the standard units for luminosity? |
watts |
A stars luminosity is the |
total amount of light that the star radiates each second |
What are the standard units for apparent brightness? |
watts per square meter |
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 |
What is the luminosity-distance formula? |
apparent brightness = (luminosity)/ (4π • (distance)^2) |
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 tar, you must measure its brightness in all wavelengths, and this is difficult to do. The only wavelengths you can measure from the surface of Earth are visible and radio wavelengths. |
Suppose you measure the parallax angle for a particular star to be .1 arcsecond. The distance to this star is |
10 parsecs |
Suppose that you measure the parallax angle for a particular star to be .5 arcsecond. The distance to this star is |
2 parsecs |
The most distant stars we can measure stellar parallax for are approximately |
100 parsecs away |
Which of the following statements about apparent and absolute magnitudes is true? |
all of the above |
The spectral sequence sorts stars according to |
surface temperature |
The spectral sequence in order of decreasing temperature is |
OBAFGKM |
Why is the spectral sequence of stars not alphabetical? |
The original alphabetical labeling did not correspond to surface temperature and thus had to be reordered |
Which of the following statements about spectral types of stars is true? |
All of the above |
Who reorganized the spectral classification scheme into the one we use today and personally classified over 400,00 stars? |
Annie Jump Cannon |
Who used the ideas of quantum mechanics to describe why the spectral classification scheme is in order of decreasing temperature? |
Cecilia Payne-Gapschkin |
Suppose you see two main sequence stars of the same spectral type. Star 1 s dimmer in apparent brightness than Star 2 by a factor of 100. what can you conclude? |
Star 1 is 10 times more distant than Star 2 |
What term is given to a pair of stars that we can determine are orbiting each other only by measuring their periodic Doppler shifts? |
Spectroscopic binary |
What term 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 best describes the axes of a Hertzsprung-Russell (H-R) diagram? |
surface temperature on the horizontal axis and luminosity on the vertical axis |
On a H-R diagram, where would we find stars that are cool and dim? |
lower right |
On a H-R diagram, where would we find stars that are cool and luminous? |
upper right |
On a H-R diagram, where would we find stars that have the largest radii? |
upper right |
On a H-R diagram, where on the main sequence would we find stars that have the greatest mass? |
upper left |
On a H-R diagram, where would we find red giant stars? |
upper right |
On a H-R diagram, where would we find white dwarfs? |
lower left |
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 |
On the main sequence, stars obtain their energy |
by converting hydrogen to helium |
The faintest star visible to the naked eye has an apparent visual magnitude of about |
6 |
What is the most common type of main- sequence star? |
M star |
What characteristic of stars has the greatest range of change in values? |
luminosity |
A star of spectral type O lives approximately how long on the main sequence? |
1 million years |
S tar of spectral type G lives approximately how long on the main sequence? |
10 billion years |
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 |
Which of the following classes refers to stars on the main sequence? |
V |
In a pulsating variable star, which characteristic of the star changes dramatically with time? |
Luminosity |
Why are Cepheid variables so important for measuring distances in astronomy? |
their luminosity can be inferred from their period |
Which of the following statements about a globular cluster is true? |
Most stars in the cluster are yellow or reddish in color |
Which of the following statements about an open cluster is true? |
All stars in the cluster are approximately the same age |
Cluster ages can be determined from |
main sequence turnoff |
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 |
What prevents a brown dwarf from undergoing nuclear fusion? |
Degeneracy pressure halts the contraction of a protostar so the core never becomes hot or dense enough for nuclear fusion |
What is the eventual fate of a brown dwarf? |
It gradually cools down and becomes even dimmer |
Where would a brown dwarf be located on an H-R diagram? |
below and to the right of the lowest part of the main sequence |
Astronomy Quiz 4
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