Astro 2

Absorption Spectrum

Dark lines on a continuous spectrum where a cooler gas absorbs specific wavelengths

Asteroid Belt

The region between Mars and Jupiter containing most of the solar system's asteroid

Aurora

Glowing lights near a planet's poles caused by charged particles entering the atmosphere along magnetic field lines

Blackbody (thermal) Radiation

EM radiation emitted by an object because of its temperature

Blueshift

A shift of light to shorter wavelengths, caused by motion toward the observer

Bohr Model

An early atomic model with electrons in fixed, quantized orbits

Charon

Pluto’s large moon

Continuous Spectrum

An unbroken rainbow of all wavelengths from a hot, dense source

Doppler Effect

The shift in observed wavelength caused by relative motion between source and observer

Dwarf Planet

A classification for bodies like Pluto that orbit the Sun but have not cleared their orbital neighborhood

Electromagnetic Spectrum

The full range of EM radiation from radio waves to gamma rays

Emission Spectrum

Bright lines produced by a hot, low-density gas at specific wavelengths

Europa

A Galilean moon of Jupiter with a cracked ice surface over a subsurface ocean

Galilean Moons

Jupiter's four large moons: Io, Europa, Ganymede, Callisto

Gas Giant

A giant planet (Jupiter, Saturn) composed mainly of hydrogen and helium with a metallic hydrogen layer

Giant-Impact Hypothesis

The modern theory that the Moon formed from debris after a Mars-sized body struck early Earth

Greenhouse Effect

Atmospheric trapping of infrared heat re-radiated from a planet's surface

Ice Giant

A giant planet (Uranus, Neptune) with a slushy water/ammonia interior layer

Kuiper Belt

A region of icy bodies beyond Neptune's orbit, including Pluto

Light-year

The distance light travels in one year

Lobate Scarp

A long cliff on Mercury formed by the shrinking of its cooling interior

Maria

Dark, flat volcanic plains on the Moon

Metallic Hydrogen

Hydrogen compressed enough to conduct electricity like a metal, found deep inside gas giants

Plate Tectonics

The movement of Earth's crustal plates driven by mantle convection

Protoplanetary Disk

The flattened, spinning disk of gas and dust from which a planetary system forms

Redshift

A shift of light to longer wavelengths, caused by motion away from the observer

Retrograde Rotation/orbit

Rotation or orbital motion opposite the usual (prograde) direction

Roche Limit

The distance within which a planet's tides can tear apart an orbiting moon or comet

Shepherd Moon

A small moon whose gravity confines and sharpens the edge of a planetary ring

Spectroscope

An instrument that splits light into its component wavelengths

Spin-Orbit Resonance

A fixed ratio between an object's rotation period and orbital period, as in Mercury's 3:2 resonance

Stefan’s Law

F = σT⁴, gives the total energy flux radiated by a blackbody

Terrestrial Planet

A small, rocky inner planet (Mercury, Venus, Earth, Mars)

Tidal Heating

Internal heating of a moon caused by gravitational flexing from its planet

Van Allen Belts

Doughnut-shaped regions where Earth's magnetic field traps charged particles

Wien’s Law

λ(peak) = 3,000,000 nm·K / T; gives the peak wavelength of blackbody emission

Zones and Belts

Light (rising gas) and dark (sinking gas) bands in a giant planet's atmosphere

Fraunhofer lines

Absorption lines due to the thin outer layer above the photosphere