Astronomical Unit (AU)The average distance from Earth to the Sun, approximately 149.6 million kilometers (93 million miles). Used as a standard unit for measuring distances within planetary systems. CoronagraphAn instrument that blocks the light of a star to reveal faint objects orbiting nearby, such as exoplanets. Essential for direct imaging of exoplanets. Earth Mass (M⊕)A unit of mass equal to the mass of Earth (5.97 × 10²⁴ kg). Exoplanet masses are often expressed relative to Earth's mass for easier comparison. Earth Radius (R⊕)A unit of length equal to Earth's radius (6,371 km). Exoplanet sizes are commonly expressed as multiples of Earth's radius. EccentricityA measure of how elliptical (non-circular) an orbit is. A value of 0 means perfectly circular, while values closer to 1 indicate increasingly elongated orbits. Equilibrium TemperatureThe theoretical surface temperature of a planet based on the amount of stellar radiation it receives, assuming no atmosphere. Measured in Kelvin (K). Hot JupiterA gas giant exoplanet that orbits very close to its star, typically completing an orbit in just a few days. These planets have extremely high surface temperatures. InclinationThe angle between a planet's orbital plane and our line of sight. A 90-degree inclination means the orbit is viewed edge-on, which is required for transit detection. Insolation FluxThe amount of stellar energy a planet receives per unit area, usually expressed relative to what Earth receives from the Sun. Used to assess habitability. Jupiter Mass (Mⱼ)A unit of mass equal to the mass of Jupiter (1.898 × 10²⁷ kg), approximately 318 times Earth's mass. Used for measuring massive exoplanets. Light-YearThe distance light travels in one year, approximately 9.46 trillion kilometers (5.88 trillion miles). One parsec equals about 3.26 light-years. Orbital PeriodThe time it takes for a planet to complete one full orbit around its star. Earth's orbital period is 365.25 days (one year). Parsec (pc)A unit of distance equal to approximately 3.26 light-years (30.9 trillion kilometers). Stellar distances in exoplanet catalogs are typically given in parsecs. Semi-Major AxisHalf the longest diameter of an elliptical orbit. For nearly circular orbits, it approximates the average distance between the planet and its star, usually measured in AU. Spectral TypeA classification of stars based on their surface temperature, labeled O, B, A, F, G, K, M from hottest to coolest. Our Sun is a G-type star. Tidal LockingWhen a planet's rotation period equals its orbital period, causing one side to permanently face the star. Common for planets orbiting close to red dwarf stars.