Classification of stars

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  • Created by: syaqub18
  • Created on: 22-05-15 10:10
what is a light year?
the distance light travels in one year
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what is an astronomical unit (AU)
mean radius of the Earths orbit around the sun (150 x 10^9)
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what is stellar parallax?
the shifting of nearby stars against background of more distant ones due to the orbital movement of the Earth around the sun
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what is a parsec?
1 parsec is defined as the distance to a star which subtends an angle of 1 arc second to the line from the centre of the Earth to the centre of the Sun
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what is an arc second?
1 degree/ 3600 seconds
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what is the luminosity of a star?
the power output of a star
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what does the brightness of a star depend on?
it is dependant on its luminosity
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what is the intenisty of radiation?
the power of the radiation/ the area
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what is the apparent magnitude of a star?
The apparent magnitude, m of a star in the night sky is a measure of its brightness which depends on the intensity of the light received from the star
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what is the absolute magnitude of a star?
The absolute magnitude, M of a star is equal to its apparent magnitude if it were placed at a distance of 10 parsecs from the Earth.
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why do stars differ in colour?
as they have a wavelength at which they emit maximum power
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what is a black body radiator?
a body which absorbs all electromagnetic radiation of all wavelengths and can also emit all wavelengths of electromagnetic radiation
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how are absorpton spectra formed?
photosphere of star gives continuous spectrum, the outermost layer/corona absorbs some wavelengths causes absorption spectra
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what are the black lines in the spectra characteristic to?
the elements and the compounds found in the corona of the star
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how can the chemical composition of a star be found out?
by comparing the absorption spectra of star to known absorption spectra of known elements
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what are balmer lines?
The hydrogen absorption lines found in the visible spectrum of the hottest stars (O, B and A only)
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how are balmer lines formed?
in these stars, hydrogen exsists which electrons in excited n=2 state, when excited by photons from photosphere of the star the move to higher energy levels,When they do this they absorb particular Balmer series light wavelengths
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what are the stages of evolution for a star like the sun?
1. NEBULA AND PROTOSTAR, 2. MAIN SEQUENCE, 3. RED GIANT, 4. PLANETARY NEBULA
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what occurs in the first stage of evolution of a star like the sun (1. NEBULA AND PROTOSTAR)?
dust and gas clouds collapse under their own gravity, become denser to form protostar, gravitational potential converted to thermal energy so particles have more kinetic energy, interior of protostar becomes hotter, if mass >0.08xsun hydrogen fuses
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what happens in the second stage of evolution of a star like the sun (2. MAIN SEQUENCE)?
radiation pressure inside star balances out gravitational forces so star is stable, greater mass of star, the brighter but wont remain on main sequence for long, temp and absolute magnitude increases gradually
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what happens in the third stage of evolution of a star like the sun (3. RED GIANT)?
once hydrogen has fused to helium in core, core collapses and outer layers expand and become cool, star swells and move from main sequence to red giant, temp of helium core increases so hydrogen and helium undergo fusion
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what happens in the fourth stage of evolution of a star like the sun (4. PLANETARY NEBULA )
when nuclear fusion in core stops, the core contacts and causes outer layers to be blown off, outer layers from planetary nebula, remaining core if less than 1.4 solar masses, it remains as white dwarf as it can't contract more
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where does a star spend most of its time on a Hertzsprung-Russell diagram?
the main sequence
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what occurs if the star is bigger than 4 solar masses?
beome red supergiants and core becomes hot enough to fuse heavy elements such as iron, has an onion like structure
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what happens if iron core of red supergiant is bigger than 1.4 solar masses?
a supernova occurs as gravitational force exceeds repulsive forces of electrons, electrons react with protons to make neutrons, core collapses and causes an expolsion, absolute magnitude of -15 to -20
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what is a standard candle?
an object of known peak absolute magnitude
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what is a neutron star?
a star which is the remnant core of a supernova, gravity causes electrons to react with protons to make neutrons
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what happens if the remnant core of a supernova is larger than 3 solar masses?
the neutrons cant withstand the gravitational forces upon it, core becomes so dense it has a gravity which light cant escape
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what is the core of a black hole referred to as?
a singularity
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what is the event horizon?
the sphere made by the schwarzchild radius as nothing inside this sphere can be observed
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what can be used as a standard candle?
a type 1a supernova
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Other cards in this set

Card 2

Front

what is an astronomical unit (AU)

Back

mean radius of the Earths orbit around the sun (150 x 10^9)

Card 3

Front

what is stellar parallax?

Back

Preview of the front of card 3

Card 4

Front

what is a parsec?

Back

Preview of the front of card 4

Card 5

Front

what is an arc second?

Back

Preview of the front of card 5
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