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Astronomy Final ch.11
Terms in this set (35)
What can Astronomers determine by looking at starlight?
Masses of stars, temperatures, compositions, distances of stars, velocities toward or away from us
Star closest to Earth other than the Sun; 4 light-years away/25 trillion miles
Formula for distance of a star
d=1/p (inverse of the parallax angle p)
What is the Stellar Parallax Effect?
positions of stars close to Earth appear to change relative to the faraway background stars as the Earth orbits around the Sun
Which exhibit a greater parallax effect, nearby or faraway stars?
What is a parsec?
the distance at which 2 objects that are 1 AU apart appear to subtend an angle of one arc second
formula for a parsec
why are parallax angles smaller than 0.01 arcsecs difficult to measure?
due to turbulance
What did Hipparchus introduce?
the magnitude scale : the classification of stars according to their apparent brightness or apparent magnitude (m)
What is apparent magnitude?
measures the brightness of stars as they appear to an observer on Earth, without regard to their distances from Earth
how much brighter are first magnitude stars than 6?
What is the brightest star?
Sirius, m = -1.44
Absolute magnitude =
M = m-5 log (d/10)
Inverse Square Law
as light moves outward from a star, it spreads out over ever increasing regions of space. As a consequence the apparent brightness of a star decreases ; intensity 1/(density)^2
the analysis of stellar spectra allows astronomers to determine...
surface temperature, chemical composition, luminosity, radial and rotational motion
the precise measurements of stellar positions
the quantitative measurement of stellar light
what reveals a star's temperature?
_____ stars have comparatively cool temperatures (3000k)
_____ stars have relatively hot temperatures ( 15,000 - 30,000k)
what determines the star's apparent color?
peak of intensity curve
what means can be used to determine stellar surface temperature?
What result from the absorption of starlight by gases, elements, molecules in the star's atmosphere?
What do the details of each spectrum indicate?
luminosity, temperature, composition, and motion
Regarding the classification of stars, what is the spectral sequence?
OBAFGKM (hottest --> coolest)
What accounts for 3/4 of mass of typical stars? What is surprising?
Hydrogen; not every star exhibits strong hydrogen absorption lines
What is required to produce strong hydrogen Balmer lines?
Stars must be hot enough to excite electrons out of n=2 state, but not so hot as to ionize a significant fraction of all the atoms
which stars are most common?
M, K, and G
cool object radiates less light from each unit of surface area than does a hot object... to be so bright, these cool stars must therefore be huge compare to main-sequence stars of the same temperature (giant stars)
dimmest, coolest main sequence stars are called...
main-sequence stars are often called...
In the Hertzsprung Russell Diagram, what do the dashed diagonal lines represent
regions of constant stellar radius
for fixed stellar radius, as surface temp increases, the star's luminosity...
3 Luminosity Classes
supergiants (1a+1b), giants of different brightness (II,III,IV), Main Sequence (V) ; correspond to different stages of stellar evolution
What is the spectroscopic parallax method?
Measure star's apparent magnitude and spectral type; from its spectrum determine the star's luminosity class; from luminosity class find star's absolute magnitude; calculate stellar distance from the distance-magnitude relation
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