Karteikarten
Star Classification
Karten in diesem Stapel (22)
- 1LuminosityThe luminosity, L, of a star is the total amount of electromagnetic radiation it
emits each second, measured in Joules per second or watts. (It is the power of the
star). - 2IntensityThe intensity, I, of a star is the energy each second from the star hitting 1m2
perpendicular to the radiation on Earth. It is measured in watts per square metre or
Wm-2 - 3Apparent MagnitudeThe apparent magnitude, m of a star is a measurement of how bright the
star appears to us on Earth. It is a subjective measurement in that it depends on
how far away the observer is from the star- the apparent magnitude would change at
different distances. - 4Number of times that one star is brighter than the other2.51^(the difference in magnitude)
- 51 AUThe astronomical unit is the mean distance from the Sun to the Earth.
- 6Arc seconds conversions1 Arc second = 1/3600 of a degree
One second = 1/60 degree
1 second = 60 arc seconds - 7The ParsecThe distance to a point in space where the
radius of the Earth’s orbit of the Sun subtends an angle of 1 arc second. (This means that the parallax angle is 1 arc second) - 8Absolute MagnitudeThe brightness (the apparent mag) of a star 10 parsecs away from Earth
- 9Black BodiesA black body completely absorbs all wavelengths of radiation falling on it and
can emit all wavelengths - 10Wien's Lawλ(max)T = constant = 2.9 × 10−3 m K
We assume that stars are black bodies and so they obey Wein’s Law. - 11Stefan's LawP = σAT^(4)
P = 4πR² σT^(4) - 12The Intensity of RadiationThe intensity of radiation hitting Earth from a star, I, in watts per meter square
is defined as the energy each second from the star hitting 1 square meter on Earth
at right angles. - 13Inverse Square LawI = L/4πD²
- 14The Sun's ClassificationThe Sun is a G2 star with a temperature of 5800K.
Absolute Magnitude of +4.77 - 15Balmer Absorbtion SpectrumThe visible absorption spectrum in hydrogen comes from electrons in the
n=2 level absorbing photons. (the number of electrons in the n=2 level depends on the temperature
of the gas and so therefore does the darkness or “intensity” of the Balmer
absorption lines. Therefore, the darkness of the lines can be used to measure the
temperature of the gas and classify it into its spectral class.) - 16Main SequenceThe star goes into an equilibrium state, where it will stay for many millions of
years, until the hydrogen in the core has run out. It is now called a Main Sequence
star. - 17Red GiantStars become Red Giants as they come to the end of their lives after they have
been on the Main Sequence. Red Giants have high luminosity but relatively low temperature. - 18White DwarfThe core of low mass stars, like the Sun, turn into White Dwarf stars at the end
of their lives after turning into a Red Giant.
The core, which is very hot, dense and with a small diameter is left behind and
is called a White dwarf. White dwarfs are mostly in the OB class and, although they
are hot, are not bright (they have a low absolute magnitude) - 19SupernovaeA supernova is where a giant star explodes at the end of its life. It has a rapid and short- lived increase in absolute magnitude. For some very massive stars, bursts of high energy https://www.goconqr.com/assets/icons/close-resource.pnggamma rays are emitted when they supernova. These bursts usually last minutes but can last hours.
The energy output of a type 1a supernova (when a white dwarf near to another star explodes) is about 1044J. This is similar to the energy given out by a star like the Sun over its whole lifetime. Other types of supernova may give out more energy - 20Neutron StarNeutron stars are very dense- about 4 x 1017 kgm-3. This density is the density
of nuclear matter. This means that neutron stars have a very strong magnetic field. The spinning neutron star is called a PULSAR- it is a very strong radio source. - 21Black HolesAn object where the escape
velocity is greater than the speed of light. It is thought that quasars are supermassive black holes at the centre of
galaxies which are very strong emitters of radio waves. - 22Schwarzchild RadiusThe event horizon is the boundary of the black hole, where the escape
velocity is the speed of light. The distance between the centre of the black hole
and the event horizon is called the Schwarzchild radius.
Schwarzchild radius, R = 2GM/C²
This equation is only approximate because Newton’s gravitational equations (used to work out the GPE formula) do not work in intense gravitational fields.
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- A-Level Physics (ASTROPHYSICS) Karteikarten am Star Classification, erstellt von Rebecca Dunning am 21/03/2017.
- Erstellt von
- Rebecca Dunning
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