19.Stars Flashcards
Absorption Line Spectrum
A spectrum consisting of dark lines at specific frequencies that have been absorbed by the gases present. Elements can only absorb certain energies, and therefore frequencies, of photons.
Astronomical Unit
The mean distance of the earth to the sun.
Big Bang Theory
The theory that the universe originated as a small, dense and hot region that expanded and cooled forming the structures in the universe we see today.
Chandrasekhar Limit
The maximum mass that a white dwarf star can have
whilst remaining stable.
Comets
Concentrated clusters of ice and dust that travel through space. When near the sun, they begin to melt and so leave a trail as they move.
Continuous Spectrum
A spectrum that covers a full range of frequencies without
any gaps. The electromagnetic spectrum is an example of a continuous spectrum.
Cosmological Principle
A principle stating that the universe is isotropic (same in
all directions to all observers) and homogenous (matter is distributed evenly).
Dark Energy
An energy that is responsible for the acceleration in the expansion of the universe which cannot be explained by any observable energy.
Doppler Effect
The apparent change in the wavelength of a wave as the source moves relative to an observer. For a source moving away the wavelength increases, for a source moving towards the observer the wavelength decreases.
Electron Degeneracy Pressure
The outwards force, resisting the inwards force of gravity, produced as a result of multiple electrons not being able to exist in identical states in an energy level.
Emission Line Spectrum
A series of bright lines at specific frequencies that
have been emitted by the gases present. Elements can only release photons of certain energies, and therefore frequencies.
Galaxies
Collections of billions of stars, planets, gases and dust, held together by gravitational attraction.
Hertzsprung-Russell Diagram
A visual representation of the lifecycle of a star. It is a plot of luminosity against temperature.
Hubble’s Law
The speed of a galaxy moving away from ours is proportional to its distance away from us. The constant of proportionality is Hubble’s constant
Light-Year
The distance travelled through space by a photon in a year.
Nebula
A cloud of dust and gas in space.
Neutron Star
An incredibly dense star that is formed when the core of a large
star collapses. Protons and electrons are forced together under gravity to form
neutrons.
Parsec
The distance at which the angle of parallax is 1 arcsecond.
Planet
A body that orbits around a star, in our case, the Sun.
Planetary Satellites
Bodies that orbit a planet. The gravitational force of the
planet’s mass provides the centripetal force of rotation.
Red-Giant
A stage in the life cycle of a star less than 3 solar masses, in which the hydrogen has run out and the temperature of the star increases. Helium nuclei fuse to form heavier elements.
Solar Systems
A collection of planets that orbit a common star.
Stefan’s Law
A law stating that the power output (luminosity) of a star is directly proportional to its surface area and its absolute temperature to the 4th power.
Stellar Parallax
The change in position of an object depending on the viewing
angle. It can be used to estimate the distance of a star, based on how much it moves relative to the background of stars in the time it takes for the earth to move half an orbit.
Supernova
When a star greater than 1.4 solar masses dies, the core collapses rapidly inward and becomes rigid. The outer layers then fall inward and rebound
off of the core in a shockwave, causing heavy elements to be fused and distributed into space in an explosion.
Universe
The name given to all space and matter.
White Dwarf
A dense star, similar mass to the sun, similar size to the earth. A
final stage of a low mass star’s life with low luminosity.
Wien’s Displacement Law
A law stating that the peak wavelength of emitted
radiation is inversely proportional to its absolute temperature.
