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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


Absolute Luminosity

The total power radiated from a star in watts


Apparent Luminosity/Brightness

Power of star light reaching Earth in .


Absolute Magnitude

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


Apparent Magnitude

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


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.


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).


Astronomical Unit

The radius of Earth’s orbit around the Sun


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.


Black holes, high-mass planets or/and failed stars – all who produce very little or no light (hence not seeable).


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.