Astrophysics and Planetary Science Lecture Flashcards

A comprehensive collection of vocabulary flashcards covering astrophysics, cosmic nucleosynthesis, planetary geology, orbital mechanics, impact cratering dynamics, and solar system formation models.

Balmer Series

The complete set of hydrogen spectral emission and absorption lines in the visible and near-ultraviolet spectrum given by the Rydberg formula $\frac{1}{\lambda} = R_H \left(\frac{1}{2^2} - \frac{1}{n^2}\right)$, where $R_H = 1.097 \times 10^7\,m^{-1}$.

Series Limit

The shortest wavelength in a spectral line series, occurring when $n \rightarrow \infty$; for the hydrogen Balmer series, it equals $\lambda = 364.6\,nm$ in the ultraviolet region.

Electroweak Era

The cosmological period between $10^{-35}$ and $10^{-10}\,s$ after the Big Bang when photons, particles, and antiparticles were continuously created and annihilated, ending when the electromagnetic and weak nuclear forces separated.

Particle Era

The era from $10^{-10}$ to $10^{-3}\,s$ after the Big Bang when expansion and cooling prevented photons from producing proton-antiproton pairs, leaving an excess of 1 proton for every 1 billion photon pairs following mass annihilation.

Proton-Proton Chain (PP I Chain)

The primary nuclear fusion reaction sequence in Sun-like main-sequence stars that converts four protons into one helium-4 nucleus, releasing a total energy of $26.7\,MeV$.

CNO Cycle

A stellar nuclear fusion process dominant in stars more massive than the Sun that uses carbon, nitrogen, and oxygen as catalysts to fuse hydrogen into helium.

Triple-Alpha Process

A nuclear fusion reaction occurring in red giant stars where three helium-4 nuclei ($^4He$) combine at extremely high temperatures to form a carbon-12 nucleus ($^{12}C$).

Helium Capture

A core nuclear burning process in high-mass stars where alpha particles ($^4He$) fuse with existing nuclei to build progressively heavier even-proton elements such as oxygen ($^{16}O$), neon ($^{20}Ne$), and magnesium ($^{24}Mg$).

r-Process

Rapid neutron capture nucleosynthesis occurring in extreme astrophysical events like merging neutron stars, responsible for generating massive quantities of chemical elements heavier than iron ($^{56}_{26}Fe$).

Cosmic Ray Spallation

Naturally occurring nuclear reactions caused by high-energy cosmic rays colliding with interstellar gas or solar system bodies, forming light elements such as lithium, beryllium, and boron.

Synthetic Elements

Man-made chemical elements with atomic numbers 95 through 118 created artificially in particle accelerators, nuclear reactors, or atomic explosions.

Tidal Locking

A dynamical equilibrium state where an orbiting celestial body's rotational period equals its orbital period, preventing any net change in rotation speed over an orbit and keeping one side permanently facing the primary body.

Runaway Greenhouse Effect

An unstable climate feedback loop where intense solar radiation evaporates surface oceans, increasing atmospheric water vapor and carbon dioxide to trap thermal energy continuously, as occurred on Venus reaching $470\,^\circ\text{C}$.

Olympus Mons

A massive shield volcano located on Mars that represents the largest volcano in the Solar System, dwarfing Mount Everest in height and surface area.

Seismic Waves

Vibrations propagating through the interior of a planet generated by quakes or impacts, used by geologists to probe and map internal density and layer structure.

Outgassing

The volcanic release of interior gases—such as water vapor, carbon dioxide, and nitrogen—trapped within a planet's mantle and crust into its atmosphere.

Galilean Moons

Jupiter's four largest satellites—Io, Europa, Ganymede, and Callisto—discovered by Galileo Galilei, each displaying distinct geologic and atmospheric phenomena.

Shepherd Moons

Pairs of small satellites orbiting near planetary ring systems that apply gravitational forces to keep ring particles constrained into sharp, narrow boundaries.

Orbital Resonance

A celestial mechanical relationship where two or more bodies exert regular, periodic gravitational tugs on each other because their orbital periods are ratios of small integers.

Kuiper Belt

A disk-shaped region of icy planetesimals and comets orbiting the Sun beyond Neptune's orbit between $30$ and $100\,AU$ in roughly orderly planar orbits.

Oort Cloud

A vast, spherical halo surrounding the Solar System out to approximately $50000\,AU$, containing roughly a trillion primitive icy comets with randomly inclined, highly eccentric orbits.

Dwarf Planet

A celestial body in direct orbit around the Sun that is massive enough to be gravitationally rounded into hydrostatic equilibrium, but has not cleared the orbital neighborhood around its path.

Universal Law of Gravitation

Newton's physical law stating that any two particles attract each other with a force $F = G \frac{m_1 m_2}{r^2}$, where $G = 6.673 \times 10^{-11}\,N\,m^2/kg^2$.

Kepler's First Law

The law of planetary motion establishing that the orbit of each planet around the Sun is an ellipse with the Sun located at one of the two foci.

Eccentricity (e)

A mathematical parameter between $0$ and $1$ describing the elongation of an orbit, where $e = 0$ corresponds to a perfect circle.

Kepler's Second Law

The orbital law stating that a line connecting a planet to the Sun sweeps out equal areas in equal times, implying planets travel faster when closer to perihelion.

Kepler's Third Law

The harmonic law relating orbital period $T$ and semimajor axis $a$ via $T^2 = \frac{4 \pi^2}{G(m_1 + m_2)} a^3$, showing that more distant planets orbit at slower average speeds.

Escape Speed

The minimum speed required for an unpropelled object to escape the gravitational potential well of a primary body, given by $v_{esc} = \sqrt{\frac{2GM}{R}}$ ($11.2\,km/s$ for Earth).

Doppler Method (Radial Velocity Technique)

An indirect exoplanet detection technique that measures periodic wavelength shifts (blueshifts and redshifts) in a star's light caused by its gravitational wobble around the system barycenter.

51 Pegasi b

The first extrasolar planet discovered around a Sun-like star (in 1995), exhibiting a 4-day orbital period and establishing the existence of 'Hot Jupiters'.

Meteoroid

A small, rocky or metallic body revolving around the Sun in space, significantly smaller than an asteroid.

Meteorite

A space rock originating from a meteoroid or asteroid that survives its passage through Earth's atmosphere and impacts the surface.

Primitive Meteorites

Unchanged meteoritic samples that have remained unaltered in composition since their formation $4.55$ billion years ago during the origin of the Solar System.

Processed Meteorites

Younger meteorites that have undergone geological processing such as melting, differentiation, or volcanism, yielding metallic iron-rich or basaltic rocky compositions.

Comet Coma

The temporary spherical halo of gas and dust sublimated from an icy comet's nucleus by solar radiation as it approaches within $3$ to $5\,AU$ of the Sun.

Tunguska Event

A massive atmospheric explosion over Siberia on June 30, 1908, caused by a disintegrating $∼ 40\,\text{meter}$ object that flattened 80 million trees without creating a surface crater.

Iridium Layer

A global sedimentary clay boundary laid down $65$ million years ago enriched with iridium, providing key geochemical evidence that a giant asteroid impact caused the K-T mass extinction.

Chicxulub Crater

A buried $170\,km$ diameter impact crater in the Yucatán Peninsula of Mexico formed $65$ million years ago by a $10$ to $20\,km$ wide impactor responsible for killing the dinosaurs.

Torino Scale

A 0-to-10 metric scale used by astronomers to categorize and communicate the potential collision hazard presented by near-Earth asteroids and comets based on impact probability and kinetic energy.

Complex Crater

An impact crater morphology spanning $5$ to $50\,km$ in diameter featuring a flat floor, terraced rim walls, and a distinct central peak formed by elastic floor rebound.

Crater Scaling Law

An empirical relationship estimating impact crater diameter $D \approx 1.8 \left(\frac{K}{g \rho}\right)^{\frac{1}{3.7}}$, where $K$ represents impactor kinetic energy, $g$ is local surface gravity, and $\rho$ is target crustal density.

Brown Dwarf

A sub-stellar object with a mass below $0.08\,M_{Sun}$ whose gravitational collapse is halted by electron degeneracy pressure before core temperatures reach $10^7\,K$, preventing sustained hydrogen fusion.

Close Encounter Hypothesis

An obsolete hypothesis suggesting that planets condensed from solar material pulled off the Sun during a near-collision with a passing star, discredited because it fails to explain planetary orbits and compositions.

Nebular Theory

The scientific model explaining that the Solar System formed $4.5$ billion years ago from the gravitational collapse of a giant spinning interstellar gas cloud called the solar nebula.

Conservation of Angular Momentum

The law of physics stating that total angular momentum $L = I \omega$ remains constant in an isolated system, causing a shrinking solar nebula to increase its rotation speed as it contracts.

Frost Line

The boundary distance in the solar nebula (around $3.5\,AU$, temperature $\approx 150\,K$) inside of which only rocks and metals condensed, and beyond which hydrogen compounds froze into solid ice.

Giant Impact Hypothesis

The leading origin model for Earth's Moon stating that a Mars-sized planetesimal (Theia) struck young Earth, blasting mantle material into orbit that rapidly accreted to form the Moon.

Hot Jupiter

A class of Jupiter-mass extrasolar gas giants orbiting extremely close to their parent stars ($< 0.1\,AU$) with short orbital periods, high temperatures, and low bulk densities.

Planetary Migration

A process where dynamic gravitational interactions between a young planet and the surrounding protoplanetary gas disk cause the planet's orbit to spiral inward toward its host star.

Transit Method

An exoplanet observation technique that measures periodic, minute dips in a star's apparent brightness as an orbiting planet passes directly between the star and the observer.