Astronomy Comprehensive Final Study Guide

Vocabulary flashcards covering all major topics listed in the five-page study guide for the comprehensive astronomy final.

Scientific Method

Systematic process of observation, hypothesis, experimentation, and conclusion used to investigate phenomena.

Deductive Method

Reasoning from general principles to predict specific results.

Inductive Method

Reasoning that builds general principles from specific observations.

Celestial Sphere

Imaginary sphere surrounding Earth onto which all celestial objects are projected.

Sidereal Day

Time (≈23h 56m) for Earth to rotate once relative to the stars.

Solar Day

Time (24h) for Earth to rotate once relative to the Sun.

Sidereal Period

Orbital period of a body measured relative to the stars.

Synodic Period

Time between successive identical configurations (e.g., conjunctions) of a body with the Sun as seen from Earth.

Precession

Slow conical wobble of Earth’s rotation axis over ~26,000 yr.

Mutation

Small periodic oscillation superimposed on Earth’s precession.

Ptolemaic Model

Geocentric universe model with epicycles explaining planetary motion.

Ellipse

Closed curve with two foci; sum of distances to foci is constant.

Kepler’s First Law

Planets move in ellipses with the Sun at one focus.

Kepler’s Second Law

A line joining planet and Sun sweeps equal areas in equal times.

Kepler’s Third Law

Orbital period squared ∝ semi-major axis cubed (P² ∝ a³).

Galileo’s Contributions

Telescopic observations (moons of Jupiter, Venus phases) supporting heliocentrism.

Newton’s First Law

Body remains at rest or uniform motion unless acted on by a force.

Newton’s Second Law

Force equals mass times acceleration (F = ma).

Newton’s Third Law

For every action there is an equal and opposite reaction.

Universal Gravitation

Every mass attracts every other mass with F = Gm₁m₂/r².

Newton’s Modification of Kepler

Generalized Kepler’s third law to include both masses: P² = 4π²a³/G(m₁+m₂).

Comet Orbits

Highly eccentric paths often following long-period or short-period trajectories.

Tidal Force

Differential gravitational force stretching a body; causes tides.

Wave Equation

Relates wave speed, wavelength, and frequency: v=λf.

Photon Energy

E = hf where h is Planck constant and f is frequency.

Continuous Spectrum

Unbroken range of colors produced by hot dense object.

Emission Spectrum

Bright lines from hot low-density gas.

Absorption Spectrum

Dark lines produced when cooler gas absorbs specific wavelengths.

Kirchhoff’s Laws of Radiation

Three rules describing conditions for continuous, emission, and absorption spectra.

Blackbody

Ideal emitter and absorber whose spectrum depends only on temperature.

Wien’s Law

Peak wavelength inversely proportional to temperature (λmax T ≈ 2.9 mm K).

Stefan-Boltzmann Law

Radiant flux F = σT⁴ for a blackbody surface.

Absolute Luminosity

Total energy output per unit time of an object.

Inverse Square Law

Apparent brightness ∝ 1/distance².

Atomic Structure

Nucleus of protons/neutrons with surrounding electron cloud.

Hydrogen Spectrum

Discrete lines from electron transitions in hydrogen atom.

Line Strengths

Intensities of spectral lines indicating element abundance and temperature.

Refracting Telescope

Instrument using lenses to gather and focus light.

Reflecting Telescope

Instrument using mirrors to gather and focus light.

CCD Camera

Charge-coupled device detector used with telescopes for imaging.

Spectrograph

Instrument that disperses light into a spectrum for analysis.

Trigonometric Parallax

Apparent shift of star position due to Earth’s orbit; basis for distance measurement.

Parsec

Distance at which 1 AU subtends 1″; ≈3.26 ly.

Apparent Magnitude

Brightness of an object as seen from Earth.

Absolute Magnitude

Apparent magnitude if object were at 10 pc.

Distance Modulus

m−M = 5 log d−5 relating apparent and absolute magnitudes to distance (pc).

Color Index (B-V)

Difference between blue and visual magnitudes; indicator of temperature.

Color Index (U-B)

Ultraviolet minus blue magnitude difference.

Doppler Effect

Shift in wavelength due to relative motion between source and observer.

Space Velocity

Total 3-D velocity of a star relative to the Sun.

Radial Velocity

Component of motion along the line of sight.

Tangential Velocity

Motion perpendicular to the line of sight.

Proper Motion

Angular change in star’s position per year on the sky.

Stellar Spectrum

Light distribution revealing temperature, composition, and motion of a star.

Proton-Proton Cycle

Fusion process converting hydrogen to helium in low-mass stars.

Binary Stars

Two stars orbiting a common center of mass.

Mass Determination (Binaries)

Using orbital parameters and Kepler’s laws to calculate stellar masses.

Spectral Classification

OBAFGKM sequence based on temperature and spectral lines.

H-R Diagram

Plot of luminosity vs. temperature (or spectral type).

Main-Sequence Star

Star fusing hydrogen in its core; diagonal band on H-R diagram.

Vogt-Russell Theorem

Stellar structure determined mainly by mass and composition.

Interstellar Medium

Gas and dust filling space between stars.

Interstellar Dust

Tiny solid particles causing extinction and reddening of starlight.

Molecular Cloud

Cold, dense gas region where molecules form and stars are born.

Spin-Flip Transition

21-cm radio emission from neutral hydrogen due to electron spin reversal.

Protostar

Contracting cloud core before nuclear fusion begins.

Red Giant

Expanded, cool star phase after core hydrogen exhaustion.

Supernova Type I

Explosion of white dwarf exceeding Chandrasekhar limit via accretion.

Supernova Type II

Core collapse explosion of massive star with hydrogen lines.

White Dwarf

Dense stellar remnant supported by electron degeneracy pressure.

Chandrasekhar Limit

Maximum mass (~1.4 M☉) for stable white dwarf.

Gravitational Redshift

Wavelength increase escaping a gravitational field.

Electron Degeneracy Pressure

Quantum pressure resisting compression of electrons.

Synchrotron Radiation

Emission from charged particles spiraling in magnetic fields at relativistic speeds.

Pulsar Lighthouse Model

Rotating neutron star beams sweep past Earth like lighthouse flashes.

Black Hole

Region where escape velocity exceeds light speed; boundary is event horizon.

Schwarzschild Radius

Distance from center to event horizon: r_s = 2GM/c².

No-Hair Theorem

Black holes described only by mass, charge, and spin.

Cepheid Variable

Pulsating star with period-luminosity relation used for distance measurement.

Open Cluster

Loose group of young stars in galactic disk.

Globular Cluster

Tightly bound, old stellar cluster in galactic halo.

Milky Way Disk

Flat component containing spiral arms, gas, and young stars.

Galactic Center Distance

Sun lies ≈8 kpc from Milky Way center.

Rotation Curve

Plot of orbital speed vs. radius; flat curve implies dark matter.

Dark Matter

Unseen mass inferred from gravitational effects on visible matter.

Population I Stars

Metal-rich, young stars in disk.

Population II Stars

Metal-poor, old stars in halo and bulge.

Density Wave Theory

Spiral arms as long-lived wave patterns compressing gas and triggering star formation.

Hubble’s Tuning Fork

Morphological classification diagram for galaxies (ellipticals, spirals, barred spirals).

Elliptical Galaxy

Smooth, featureless galaxy with little gas and star formation.

Spiral Galaxy

Disk galaxy with spiral arms and ongoing star formation.

Primary Distance Indicator

Method (e.g., parallax) requiring no prior calibration.

Secondary Distance Indicator

Technique calibrated by primary indicators (e.g., Cepheids).

Tertiary Distance Indicator

High-distance methods calibrated by secondary indicators (e.g., Hubble law).

Hubble’s Law

Recession velocity ∝ distance (v = H₀d).

Hubble Constant

Rate of cosmic expansion; inverse gives age estimate of universe.

Big Bang Theory

Model that universe began from hot dense state and has been expanding.

Cosmic Microwave Background

Relic 2.7 K radiation filling universe; evidence for Big Bang.

Radio Galaxy

Active galaxy emitting strong radio lobes.

Seyfert Galaxy

Spiral galaxy with bright, variable nucleus emitting strong emission lines.