Stars, Galaxies, and Cosmology Vocabulary

Flashcards covering key vocabulary related to stars, galaxies, cosmology, and astrophysics, based on the lecture notes provided.

Planets

Objects with mass sufficient for their own gravity to force them into a spherical shape, where no nuclear fusion occurs, and the object has cleared its orbit of other objects.

Dwarf Planets

Planets where the orbit has not been cleared of other objects.

Planetary Satellites

Bodies that orbit a planet.

Asteroids

Objects which are too small and uneven in shape to be planets, with a near-circular orbit around the sun.

Comets

Small, irregularly sized balls of rock, dust, and ice that orbit the sun in eccentric elliptical orbits.

Solar Systems

Systems containing stars and orbiting objects like planets.

Galaxies

A collection of stars, dust, and gas, typically containing around 100 billion stars.

Nebulae

Gigantic clouds of dust and gas; the birthplace of all stars.

Protostar

The resultant sphere of very hot, dense dust and gas formed by gravitational collapse in nebulae; a precursor to a star.

Main Phase (of a star)

The period when a star is in stable equilibrium, with gravitational forces balanced by radiation and gas pressure.

Solar Mass (M☉)

1.99 x 10^30 kg; the mass of our sun's core, used as a unit to measure the mass of other stars.

Red Giant

A stage in the evolution of a low-mass star where the star expands and cools as hydrogen supplies dwindle and helium fusion begins in the outer shell.

White Dwarf

A very dense core that remains after a red giant has shed its outer layers as a planetary nebula; no fusion occurs.

Chandrasekhar Limit

1.44M☉; the maximum mass of a white dwarf star. Above this limit, electron degeneracy pressure cannot prevent collapse.

Red Supergiant

A star that evolves from a massive star as hydrogen depletes, and helium fuses into heavier elements.

Type 2 Supernova

The explosive death of a massive star, resulting in the ejection of outer layers and core collapse.

Neutron Star

An extremely small, dense star composed mostly of neutrons, formed from the core of a massive star after a supernova.

Black Hole

A region in spacetime with gravitational forces so strong that nothing, not even photons, can escape.

Hertzsprung-Russell (HR) Diagram

A diagram that plots the stellar luminosity of a star against its temperature, used to classify stars.

Emission Line Spectra

A spectrum appearing as a series of colored lines on a black background, unique to each element due to its unique set of energy levels.

Continuous Line Spectra

A spectrum where all visible wavelengths of light are present, typically produced by atoms of heated solid metals.

Absorption Line Spectra

A spectrum showing a series of dark spectral lines against the background of a continuous spectrum, with each line corresponding to a wavelength of light used to excite atoms of that element.

Spectroscopy

The technique used to identify elements based on the wavelengths of light emitted when atoms in a gas are exited.

Diffraction Grating

Components with regularly spaced slits that can diffract light, separating different colors of light at different angles based on their wavelengths.

Wein’s Displacement Law

Relates the temperature of a star with the peak wavelength of the electromagnetic radiation emitted by the star. 𝜆max ∝ 1/T.

Stefan’s Law

Relates the temperature of a star with its luminosity L. L ∝ 4πr^2 T^4.

Astronomical Unit (AU)

1.5 x 10^11 m. The average distance from the Earth to the sun, used to express the distance of planets from the sun.

Light Year (ly)

9.46 x 10^15 m. The distance light travels in one year, used to express the distances to stars and other galaxies.

Parsec (pc)

3.1 x 10^16 m. The distance at which a radius of 1 AU subtends an angle of 1 arcsecond.

Stellar Parallax

The apparent shift in the position of a nearby star against a backdrop of distant objects, used to measure the distance to nearby stars.

Cosmological Principle

The principle that the universe is isotropic and homogenous, and the laws of physics are universal.

Isotropic

The universe is the same in all directions to every observer, and it has no center or edge.

Homogenous

Matter is uniformly distributed - for a large volume of the universe, the density is the same.

Doppler Effect

The apparent shift in wavelength occurring when the source of waves is moving.

Hubble’s Law

The recessional velocity v of a galaxy is proportional to its distance from Earth: V = H0d.

Big Bang Theory

The theory that all objects were initially contained in a singularity, which suddenly expanded outwards, and the universe has continued to expand since then.

Dark Energy

A hypothetical form of energy which fills all of space and accelerates its expansion.

Dark Matter

A hypothetical type of matter that is not seen through telescopes and doesn’t interact with light, but contributes to the mass of galaxies.