Module 5.5 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.
Black Hole
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.
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
How are protostars formed
In nebulae, there are regions that are more dense than others. Over time, gravity draws matter towards them and combined with the conservation of angular momentum, causes them to spin inwards to form a denser centre
- GPE is converted into thermal energy which heats up the center. The resultant sphere of very hot, dense dust and gas is a protostar
How are main sequence stars formed from protostar
- The temperature and pressure must be high enough for hydrogen gas nuclei in the protostar to overcome the electrostatic forces of repulsion and undergo nuclear fusion to convert hydrogen into helium.
- When fusion begins the protostar becomes a main sequence star where the outward pressure due to fusion and the inward force of gravity are in equilibrium
Describe the process of electrons exciting in discrete energy levels
Electrons bound to an atom can only exist in certain discrete energy levels. The electron cannot have an energy value between two levels.
- When an electron moves from lower energy state to a higher energy state in is “excited”. This requires the input of external energy
What are emission line spectra and how are they formed
- A series of coloured lines on a black background
- When light passes through the outer layers of a star, the electrons in the atoms absorb photons and become excited. They then de-excite releasing photons of specific wavelengths. These photons are detected on Earth and have wavelengths characteristic of the elements in the outer layers shown as emission line spectra
What is a continuous line spectra
Continuous line spectra - where all visible wavelengths of light are present. They are produced by atoms of solid heated metals
What are absorption line spectra
A series of dark spectral lines against the background of the continuous spectrum, with each line corresponding to a wavelength of light absorbed by atoms in the outer layers of a star. The dark lines are at wavelengths that are characteristic of elements in the outer layers
What are diffraction grattings
Components with regularly spaced slits that can diffract light. Different colours of light have different wavelengths and so will be diffracted at different angles
Define light year
The distance travelled by light in a vacuum in one year. In metres this is 9.45x10^15m
What is redshift
Red shift is the shift in wavelength and frequency of waves from a retreating sources. Cosmological redshift is evidence for the Big Bang
What are quasars
A quasar is a nucleus of an active galaxy, a supermassive black hole surrounded by a disc of matter. As matter falls into the black hole, jets of radiation are emitted from the poles of the quasar
What suggests that they are extremely distant objects
Large optical red shift shows quasars are the most distant observable objects. From the inverse square law for intensity we know they are extremely powerful, with the same energy output as several galaxies. They were initially found to be powerful radio sources but with further telescope developments we now know they emit all wavelengths of EM radiation
