34 terms

Astrophysics Terms

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luminosity
total power radiated by a star in W
apparent brightness
power received per unit area in W/m^2
the brightness of a star as seen from earth
apparent magnitude
a measure of the brightness of a star as seen by an observer on earth
the brighter it appears, the lower its magnitude
absolute magnitude
a measure of the brightness of a star as seen from 10 parsecs away
O
blue
B
blue-white
A
white
F
yellow-white
G
yellow
K
orange
M
orange-red
binary stars
pair of stars that orbit around a common center of mass
visual binary
a binary that can be distinguished as two stars from a telescope
spectroscopic binary
a binary that can be identified by the blue and red shifts in its spectrum of light
eclipsing binary
a binary that can be identified by its periodic variation in brightness, as caused by the two stars eclipsing each other
magnitude scale
scale measuring apparent brightness of stars
brightest to dimmest-...1, 2, 3, 4, 5...
each step equates to a brightness decrease if 2.512
spectroscopic parallax
procedure to estimate luminosity of a star from its spectrum
assumes spectra from distant stars is same as spectra from nearby ones
can use H-R diagram to estimate the luminosity
then can find distance from equation for brightness
cepheid variable
outer layers undergo periodic compression and contraction that produces a periodic variation in luminosity
olber's paradox
if the universe is infinite, uniform and static, why isn't the night sky entirely bright
solutions:
1. universe is not infinite
2. universe is not static-it is expanding
microwave background radiation
microwave radiation coming towards earth from all directions, no apparent source
open universe
our universe will expand forever
force of gravity slows it down a little bit, but wont stop it
LOW density universe
closed universe
our universe will eventually cease to expand and then collapse back in on itself
force of gravity is very strong
HIGH density universe
flat universe
our universe will slow its rate of expansion, but it takes an infinite time to get to rest
CRITICAL density
nucleosynthesis
creation of nuclei of different elements as a result of fission reactions
in the main sequence
when a star is fusing hydrogen into helium
eventually hydrogen becomes rare, and energy is not enough to fight gravity
red giant
core collapses due to gravity, which increases the temperature and makes helium fusion possible
star becomes massive, outer layers cool off
chandrasekhar limit
critical mass- 1.4 solar masses
if a star starts out >4 solar masses, it will be above the limit
white dwarf
less than 1.4 solar masses
red supergiant
greater than 1.4 solar masses
experiences a supernova and then either becomes a neutron star or a black hole
pulsar
rotating neutron star that emits weak radio wave energy and pulsates rapidly at a precise frequency
quasar
very far away source of light and radio waves with a large red-shift
wien's law
the higher the temperature of a body the shorter the wavelength of it's maximum radiation
hotter = shorter wavelength
hubble's law
the recessional velocity is proportional to the distance away from earth
Oppenheimer-Volkoff limit
2-3 solar masses
past which a neutron star becomes a black hole