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38 Cards in this Set

  • Front
  • Back
Arc Second
One degree split up into seconds (1/3600 of a degree).
Light Year
The distance light travels during one year

ly
Absolute Luminosity
The total power radiated from a star in watts

W
Apparent Luminosity/Brightness
Power of star light reaching Earth in .

b
Absolute Magnitude
Apparent Magnitude of a star at a standard distance of 10 parsec.

M
Apparent Magnitude
How bright a star looks (scale 6 to 1, 1 being the brightest).

m
Black Body
Hot body who’s emission spectrum depends on its temperature only (stars are considered black bodies because they emit all energy produced).
Black Body Radiation
Radiation from a theoretical “perfect” emitter.
Cepheid Variable Star
Stars that varies periodically in size (not mass!!) and hence luminosity (used to determine distances greater than 10 Mpc).
Binary Star
Two or more stars that orbit around each other.
Planetary Order
Mercury, Venus, Earth, Mars, Asteroid Belt, Jupiter, Saturn, Neptune, Uranus, Pluto
Eclipsing Binaries
Two stars that regularly eclipse each one another causing a periodic variation in brightness.
Red Giant
A large and relative cool star in one of the later stages of its life. The source of its energy is fusion of some other element than hydrogen.
Red Super Giant
A very large mass and relative cool star in one of the later stages of its life. The source of its energy is fusion of some other element than hydrogen.
White Dwarf
A small and relative cool star at one of the possible final stages of a star’s life. Fusion is no longer taking place and hence it is cooling down.
Parsec
1 parsec is the distance which will give a parallax angle of exactly 1 arc second, with 1 AU as the baseline (3.26 light years).

pc
Astronomical Unit
The radius of Earth’s orbit around the Sun

AU
Red Shift
Increase in wavelength emitted from galaxies and stars moving away from Earth. This can either be due to the Doppler Effect or expansion of space (which expands the wave).
Critical Density
The theoretical density of the universe necessary to create a “flat” universe after an infinite amount of time
Dark Matter
Not seeable matter that must exist to explain the lack of observable gravitational matter that make the stars orbit the galactic centre.
MACHOs
Black holes, high-mass planets or/and failed stars – all who produce very little or no light (hence not seeable).
WIMPs
A new type of particle that can prove the existence of dark matter.
Newton's First Postulate about the Universe
The universe is infinite.
Newton's Second Postulate about the Universe
Mass is uniformly distributed in space.
Obler's Paradox
Why is not the sky bright at night if there is a bright star at every point in the sky? (Inverse Square Law)
Wein's Displacement Law
Wavelength of radiation with maximum intensity (peak wavelength) is inversely proportional to the temperature of the black body.
Stefan-Boltzman Law
Links the total power output radiated by a black body to its temperature.
Frame of Reference
Set of rulers from which measurements can be made.
Galilean Transformations
Relate distance and velocity in one frame of reference to another.
Inertial Frame of Reference
Frame of reference where the laws of inertia (Newton’s Laws) apply.
Proper Time
The time measured by an observed who is at the same place as the event.
Proper Length
The length measured by an observer who is at the same place as the event.
Rest Mass
The mass of a body measured by an observer who is at rest relative to the body.
Relativistic Mass
The mass of a body measured by an observer who has a velocity other than zero relative to the body.
Rest Mass Energy
The energy “locked up” in the mass of the body at rest.
Total Energy
The sum of a body’s rest mass energy and relativistic kinetic energy.
Einstein's First Postulate of Special Relativity
The laws of Physics are the same in every inertial frame of reference.
Einstein's Second Postulate of Special Relativity
Light propagates through empty space with a definite speed c, independent of the speed of the source or observer.