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Unit 9
H-R diagram
25
Astronomy
Undergraduate 2
11/04/2012

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Term
A parsec is
Definition
the distance to a star with a parallax of one second of arc
Term
To an observer on the Earth, a star of apparent magnitude +1 appears ___ than a star of apparent magnitude +2
Definition
brighter
Term
What is the difference between absolute and apparent magnitude of a star?
Definition
Absolute magnitude is a fundamental property of the star which does not change, whereas apparent magnitude depends on its distance from Earth
Term
In the constellation of Orion, the star Rigel has a distinct blue color and the star Betelgeuse has a strong red color. This means that
Definition
Rigel is hotter then Betelgeuse
Term
The luminosity of a star is
Definition
its total energy output into all space
Term
Which stellar class is the coolest?
Definition
M
Term
Cool stars can be luminous if they
Definition
are large in radius
Term
Most of the brightest stars in our sky are
Definition
Hot F, B, and O stars or gaints
Term
Most of the stars near the sun are
Definition
cool and dim
Term
Most stars in the galaxy are in spectral class
Definition
K and M
Term
The first reliable way to tell how far away a star is was
Definition
angular parallax
Term
You would expect that O, A and K stars would all
Definition
be located on the main sequence
Term
You would expect an O star to emit most of its radiation in the
Definition
Ultraviolet band
Term
The mass of a star can be obtained most easily if the star is
Definition
part of a binary system
Term
In this H-R diagram, stars with higher temperatures would be located
Definition
at the left side of the graph
Term
In this H-R diagram, dim, low-luminosity stars would be located
Definition
at the bottom of the graph
Term
In this H-R diagram, the mass of stars increases
Definition
E to A
Term
Where on this diagram would you expect to find most hydrogen-burning stars?
Definition
in the shaded area between E and A
Term
In which area would you find giant stars?
Definition
B
Term
In which area of the graph would you expect to find the Sun?
Definition
C
Term
In which area of the graph would you expect to find most stars in the galaxy?
Definition
between E and C
Term
In which area of the graph would you expect to find the brightest stars in the night sky?
Definition
between C and A
Term
You would find the shortest-lived adult stars in region
Definition
A
Term
You would find the longest-lived hydrogen-burning stars in region
Definition
E
Term
Stellar class describes a star's
Definition
surface temperature and absorption spectra
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