35 terms

Astronomy Exam 3

Descriptive Astronomy Test 3
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star
a glowing ball of gas held together by its gravity and powered by nuclear fusion
Sun facts
Radius: 696,000 km (100 Earth radii)
Mass: 1.99*10^30 kg
Average Density : 1410 kg/m^3
Rotation Period 24.9 days (equator); 29.8 days (poles)
Surface temp.: 5780K
Luminosity: 3.86 10^26 Watts
Chemical Composition of Sun
Hydrogen 71 % of mass
Helium 27.1 % of mass
Oxygen .97% of mass
Carbon .4 % of mass
Photosphere
part of the sun that has the right conditions that the light produced is released out into the atmosphere called the surface 500km
Corona
Glow around the sun
part of the atmosophere
Luminosity
one of the basic properties used to characterize stars, luminosity is defined as the total energy radiated by a star each second, at all wavelengths
Sun Fusion
occurs in the core where the temp. is about 15 million K and the density is about 160,000 kg/m^3
Sunspots
sunspots are dark regions in the photosphere
-typically about 10,000 km across (size of earth)
-appear dark because they are cooler than the surrounding gases
-region where the suns magnetic field is concentrated in leaving and entering the photosphere
-come in pairs
Sunspot cycle
an 11 year cycle in which the number of sunspots reaches a maximum and minimum
half the duration of the solar cycle
-magnetic field cycle
Solar Cycle
a 22 year cycle in which the Sun's magnetic pole reverses and returns to their original configuration
nuclear fusion
mechanism of energy generation in the core of the Sun, in which light nuclei are combined, or fused, into heavier ones, releasing energy in the process
-crucial point is during a fusion reaction, the total mass decrease the mass of nucleus 3 is less than the combined masses of nuclei 1 and 2
hydrostatic equilibrium
gas pressure cancels out the gravity pulling in and makes the stars the size that they are
- if gas pressure excels bigger that leads it to become a black hole (gravity wins)
parallax
look at apparent motion of an object against distance background from 2 vantage points; knowing baseline allows calculation of distance use tis to measure how far away stars are
apparent brightness
how bright a star appears when viewed from Earth
brightness
the amount of energy striking per unit area per unit time of some light sensitive surface (we can directly measure this)
-absolute brightness = luminosity
brightness=luminosity/ (4PiDistance^2)
high luminosity
stars are high mass
low luminosity
stars are low mass
Main occupation of stars
fusing hydrogen to helium
planetary nebula
the ejected envelope of a red-giant star, spread over a volume roughly the size of our solar system
nova
a star that suddenly increase in brightness, often by a factor of as much as 10,000, then slowly fades back to its original luminosity. A nova is the result of an explosion on the surface of a white-dwarf star, cause by matter falling onto its surface from the atmosphere of a binary companion
supernova
explosive death of a star, caused by the sudden onset of nuclear burning (type 1) or an enormously energetic shock wave (type 2) one of the most energetic events of the universe, a supernova may temporality outshine the rest of the galaxy in which it resides
supernova remnant
the scattered glowing remains from a supernova that occurred in the past. The Crab Nebula is one of the best-studied supernova remnants
white dwarf
a dwarf star with sufficiently high surface temperature that it glows white
neutron star
a dense ball of neutrons that remains at the core of a star after a supernova explosion has destroyed the rest of the star. Typical neutron stars are about 20km across and contain more mass than the sun
black hole
a region of space where the pull of gravity is so great that nothing- not even light- can escape. A possible outcome of the evolution of a very massive star.
Chandrasekhar Limit
The maximum size of a stable white dwarf, approximately 3 × 1030 kg (about 1.4 times the mass of the Sun). Stars with mass higher than the Chandrasekhar limit ultimately collapse under their own weight and become neutron stars or black holes. Stars with a mass below this limit are prevented from collapsing by the degeneracy pressure of their electrons
Solar Wind
an outward flow of fast-moving charged particles from the Sun
determining stellar luminosity
first must determine the star's apparent brightness by measuring the amount of energy detected through a telescope in a give amount of time. 2nd stars distance must be measure by parallax for nearby stars and by other means, luminosity can then be found using the inverse-square law
apparent brightness (symbol representing proportionality) luminosity/ distance^2
apparent magnitude
the apparent brightness of a star, expressed using the magnitude scale
absolute magnitude
the apparent magnitude a star would have if it were placed at a standard distance of 10 parsecs from Earth
standard candle
any object with an easily recognizable appearance and known luminosity, which can be used n estimating distances. supernovae, which all have the same peak luminosity (depending on type), are good examples of standard candles and are used to determine distances to other galaxies
Spectroscopic Parallax
method of determining the distance to a star by measure its temperature and then determining its absolute brightness by comparing with a standard Hertzsprung-Russell diagram. The absolute and apparent brightness of the star give the star's distance from Earth
variable star
a star whose luminosity changes with time
parsec
the distance at which a star must lie in order for its measured parallax to be exactly 1 arc second; 1 parsec equals 206,000 AU
magnitude= 3.3 light-years
Hertzsprung-Russell
hot stars on left
coller, red stars to the right
high luminosity, higher temp move to the upper left
lower luminosity, lower temp to the lower right
lower left= white dwarfs, smaller stars
upper right= red giants, bigger stars
upper left are the stars have a short lifetime
lower right stars have a longer lifetimes
young stars can be anywhere on graph