International Space Olympiad 2026 Reference Book Flashcards

Comprehensive vocabulary flashcards covering key astronomy, astrophysics, celestial mechanics, and planetary science concepts from the International Space Olympiad 2026 Super Senior Reference Book.

Right Ascension

Celestial coordinate measured in hours, minutes, and seconds eastward along the celestial equator; it serves as the celestial equivalent of terrestrial longitude.

Declination

Celestial coordinate measured in degrees north (positive) or south (negative) of the celestial equator; it serves as the celestial equivalent of terrestrial latitude.

Azimuth

Celestial coordinate in the horizontal coordinate system that measures direction clockwise around the horizon.

Sidereal Day

The time Earth takes to complete one full rotation relative to distant fixed stars, lasting approximately $23\text{ hr } 56\text{ min}$—about $4\text{ minutes}$ shorter than a mean solar day.

Precession

A slow, continuous change in the orientation of a celestial body's rotational axis caused mainly by lunar and solar torques, completing a full cycle for Earth in approximately $26,000\text{ years}$.

Helioseismology

The study of vibrations and sound-wave oscillations within the Sun used to probe its internal structure and dynamics.

Eccentricity

An orbital parameter describing the elongation of an orbit, ranging from $0$ for a perfectly circular orbit to values approaching $1$ for highly elongated elliptical orbits.

Orbital Inclination

An orbital parameter that measures the tilt of an object's orbital plane relative to a standard reference plane, such as the ecliptic plane.

Ascending Node

The specific point where an orbiting satellite or body crosses the equatorial or reference plane moving from south to north.

Radiative Zone

The region of the solar interior located between the core and the convective zone, where energy is transported outward primarily through photon diffusion.

Proton-Proton Chain

The primary nuclear fusion mechanism in lower-mass stars like the Sun, converting four protons into one helium nucleus along with positrons and neutrinos.

CNO Cycle

A hydrogen fusion pathway dominating in stars with high core temperatures, where carbon, nitrogen, and oxygen nuclei act as catalysts.

Solar Corona

The outermost layer of the Sun's atmosphere, visible during total solar eclipses, characterized by temperatures reaching millions of kelvin.

Sunspots

Cooler, dark regions on the Sun's photosphere created by intense local magnetic fields inhibiting normal surface convection.

Maunder Minimum

A historical period from roughly 1645 to 1715 characterized by unusually few sunspots and reduced solar activity.

Radial Velocity

The component of a celestial object's velocity directed along the observer's line of sight, typically determined using the Doppler effect.

Kirkwood Gaps

Unpopulated regions in the semi-major axis distribution of the Asteroid Belt caused by orbital resonances with Jupiter's gravitational field.

Trans-Neptunian Objects (TNOs)

A broad classification of minor bodies and dwarf planets in the Solar System that orbit the Sun at average distances beyond Neptune.

Nice Model

A dynamical model of Solar System evolution proposing that giant planets underwent significant migration from initial orbits closer to the Sun to their current positions.

Tidal Heating

Internal heating of a moon or planet generated by gravitational friction caused by varying tidal stresses in an eccentric orbit.

Stellar Parallax

The apparent shift in position of a nearby star against background stars when viewed from opposite sides of Earth's orbit, used to calculate stellar distance.

Parsec

A unit of astronomical distance defined as the distance at which $1\text{ AU}$ subtends a parallax angle of $1\text{ arcsecond}$, equal to approximately $3.26\text{ light-years}$.

Apparent Magnitude

A measure of the brightness of a star or celestial object as observed from Earth, where smaller or negative values indicate brighter objects.

Absolute Magnitude

A measure of an object's intrinsic luminosity, defined as the apparent magnitude it would have if placed at a standard distance of $10\text{ parsecs}$.

O-Type Stars

The hottest, most massive spectral class of main-sequence stars, characterized by blue color and strong absorption lines of ionized helium.

Space Velocity

The total three-dimensional velocity of a star through space relative to the Sun, calculated by combining radial velocity and proper motion.

Equation of Time

The difference between apparent solar time (sundial time) and mean solar time (clock time), which reaches zero four times a year.

Schwabe Cycle

The roughly 11-year periodic cycle in solar activity, during which the number of sunspots and solar flares rises and falls.

Chandrasekhar Limit

The maximum mass of a stable white dwarf star supported by electron degeneracy pressure, equal to approximately $1.4$ solar masses.

Line of Nodes

The line formed by the intersection of an object's orbital plane with a reference plane (such as the ecliptic or equatorial plane).

Dwarf Planet

A celestial body orbiting the Sun with sufficient mass for hydrostatic equilibrium (spherical shape) that has not cleared its orbital neighborhood and is not a satellite.

Hubble's Law

The observational law stating that the recession velocity of distant galaxies is directly proportional to their distance from the observer.

Cosmic Microwave Background (CMB)

Uniform background thermal radiation filling the observable Universe, serving as key observational evidence for the Big Bang.

Tropical Year

The time interval between successive vernal equinoxes, forming the basis for solar calendars.

Lagrange Points

Positions in an orbital configuration where the gravitational forces of two large masses and the centrifugal force balance, allowing smaller objects like Trojan asteroids to remain stable.

Faculae

Bright, elevated magnetic structures on the solar surface that emit more light than surrounding photospheric regions.

Laplace Resonance

An orbital resonance in which three celestial bodies exert periodic gravitational influence on each other, as seen in Jupiter's moons Io, Europa, and Ganymede (1:2:4 orbital period ratio).

Retrograde Motion

The apparent backward motion of a planet across the sky relative to fixed background stars, caused by Earth passing the planet in its shorter, faster orbit.

Coronal Mass Ejection (CME)

A huge outburst of solar plasma and magnetic fields ejected from the corona into space, capable of disrupting satellites, GPS signals, and electrical grids on Earth.

Big Bang Nucleosynthesis

The formation of light atomic nuclei (primarily hydrogen and helium isotopes) during the first few minutes after the Big Bang.

Habitable Zone

The circumstellar region where planetary surface temperatures allow liquid water to exist, considered critical for life.

Grand Tack Hypothesis

A Solar System evolution model proposing that Jupiter migrated inward toward the Sun before reversing direction ("tacking") outward due to resonance with Saturn.

Rayleigh Scattering

The scattering of light off particles much smaller than light's wavelength, which scatters short blue wavelengths more strongly than longer red wavelengths and gives Earth's sky its blue appearance.

Geodynamo

The mechanism inside Earth's outer core where convection currents in molten iron generate Earth's magnetic field.

Low Earth Orbit (LEO)

An orbit extending from approximately $160\text{ km}$ to $2,000\text{ km}$ above Earth's surface, featuring short orbital periods ideal for Earth observation and space stations.

Geostationary Earth Orbit (GEO)

A circular orbit situated $35,786\text{ km}$ directly above Earth's equator where a satellite's period matches Earth's rotation, making it appear stationary in the sky.