Astronomy Vocabulary

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  • absolute magnitude

    (n.) measure of a celestial object's intrinsic brightness, standardized distance

  • accretion disk

    (n.) rotating disk of matter spiraling into a celestial body

  • active galactic nucleus

    (n.) bright central region of some galaxies, high energy emissions

  • airborne observatory

    (n.) telescope mounted on an aircraft or balloon for observations

  • albedo

    (n.) reflectivity of a surface, ratio of reflected to incident light

  • albedo feature

    (n.) surface marking distinguished by reflectivity differences

  • Am star

    (n.) chemically peculiar star with strong metal lines

  • aphelion

    (n.) point in orbit farthest from the sun or star

  • apoapsis

    (n.) furthest point in orbit around a focus point

  • apogee

    (n.) highest point in satellite orbit around Earth

  • apparent magnitude

    (n.) brightness of object as seen from Earth

  • appulse

    (n.) close approach of celestial objects as seen from a vantage point

  • apsis

    (n.) closest or furthest point in an orbit around a focus

  • argument of periapsis

    (n.) angle from ascending node to periapsis in orbit

  • artificial satellite

    (n.) human-made object orbiting a planet or star

  • ascending node

    (n.) point where orbit crosses celestial plane moving north

  • aspect

    (n.) angle between observer, object, and reference point

  • asterism

    (n.) recognizable pattern of stars within a constellation

  • asteroid

    (n.) small rocky body orbiting the Sun, smaller than planets

  • asteroid belt

    (n.) region between Mars and Jupiter with numerous asteroids

  • astrobiology

    (n.) study of life in the universe and its origins

  • astrodynamics

    (n.) study of motion of celestial bodies and spacecraft

  • astrogeology

    (n.) geology of planets and moons in the solar system

  • astrometric binary

    (n.) star system identified via precise position measurements

  • astrometry

    (n.) measurement of celestial object positions and motions

  • astronomical body

    (n.) natural object in space, like planets or stars

  • astronomical catalogue

    (n.) organized list of celestial objects

  • astronomical object

    (n.) any physical entity in space observed visually or otherwise

  • astronomical symbol

    (n.) shorthand notation for celestial objects or points

  • astronomical unit

    (n.) average distance from Earth to Sun (about 149.6 million km)

  • astronomy

    (n.) scientific study of celestial objects and phenomena

  • astrophotography

    (n.) photography of celestial objects and phenomena

  • astrophysics

    (n.) physics governing celestial bodies and universe

  • atmosphere

    (n.) gaseous envelope surrounding a planet or star

  • axial precession

    (n.) slow westward shift of rotational axis over time

  • axial tilt

    (n.) angle between rotational axis and orbital plane

  • axis of rotation

    (n.) imaginary line around which an object spins

  • azimuth

    (n.) compass angle of an object from a reference direction

  • Babcock model

    (n.) solar magnetic cycle explaining sunspot patterns

  • barycenter

    (n.) center of mass of two or more orbiting bodies

  • baryogenesis

    (n.) theoretical process creating matter-antimatter imbalance

  • Big Bang

    (n.) universe's initial explosive expansion origin event

  • binary star

    (n.) system of two stars orbiting a common center

  • black hole

    (n.) region of space with gravity so strong nothing escapes

  • blazar

    (n.) active galactic nucleus with jet pointing toward Earth

  • brown dwarf

    (n.) failed star with insufficient mass for nuclear fusion

  • bulge

    (n.) central dense region of a spiral galaxy

  • calibrator star

    (n.) star used as reference for measurements or calibration

  • celestial equator

    (n.) projection of Earth's equator onto celestial sphere

  • celestial mechanics

    (n.) study of motion of celestial objects

  • celestial meridian

    (n.) great circle passing through zenith and poles

  • celestial pole

    (n.) point where Earth's axis intersects celestial sphere

  • celestial sphere

    (n.) imaginary sphere with stars fixed on its inside

  • centaur

    (n.) small Solar System body between asteroids and comets

  • central massive object

    (n.) dense core exerting gravitational influence

  • chromosphere

    (n.) sun's outer atmospheric layer above the photosphere

  • chromospheric activity index

    (n.) measure of solar or stellar activity levels

  • circumstellar disc

    (n.) dust and gas ring around a star or planet

  • clearing the neighbourhood

    (n.) process of dominating surrounding space in orbit

  • color index

    (n.) measure of star's color and temperature differences

  • comet

    (n.) icy body with glowing tail when near the Sun

  • commensurability

    (n.) orbital ratio of two bodies with simple integer ratio

  • common proper motion

    (n.) stars moving together through space

  • compact star

    (n.) dense stellar remnant like white dwarf or neutron star

  • compact stellar nucleus

    (n.) dense central core of a galaxy or star cluster

  • conjunction

    (n.) alignment of celestial bodies in apparent line

  • constellation

    (n.) recognized pattern of stars forming mythic shapes

  • corona

    (n.) sun's outer atmosphere visible during eclipses

  • coronal loop

    (n.) magnetic arc of plasma in the solar corona

  • coronal mass ejection

    (n.) massive burst of solar plasma and magnetic fields

  • cosmic distance ladder

    (n.) method judging celestial distances with multiple steps

  • cosmic dust

    (n.) tiny solid particles in space affecting light and heat

  • cosmic microwave background

    (n.) thermal radiation from early universe

  • cosmic ray

    (n.) high-energy particles from space impacting Earth

  • cosmogony

    (n.) theory of universe's origin and formation

  • cosmology

    (n.) study of universe's structure, origin, and evolution

  • critical rotation

    (n.) rotation speed leading to shape deformation or breakup

  • critical velocity

    (n.) speed at which star's equator becomes unstable

  • culmination

    (n.) highest point a celestial object reaches in sky

  • debris disk

    (n.) material around star from collisions or remnants

  • declination

    (n.) angular distance north or south of celestial equator

  • decretion disk

    (n.) material ejected outward from a star as disk

  • degenerate star

    (n.) dense stellar remnant like white dwarf or neutron star

  • descending node

    (n.) point where orbit crosses celestial plane heading south

  • detached object

    (n.) distant small Solar System body outside Neptune's influence

  • direct motion

    (n.) apparent movement of celestial objects along the sky

  • diurnal motion

    (n.) daily apparent movement of stars due to Earth's rotation

  • double star

    (n.) pair of stars appearing close in the sky

  • dust astronomy

    (n.) study of cosmic dust and its effects

  • dwarf planet

    (n.) small planet-like body orbiting the sun, not classified as planet

  • dwarf star

    (n.) small, low-mass star, often red or brown

  • eccentricity

    (n.) measure of how elliptical an orbit is

  • ecliptic

    (n.) plane of Earth's orbit around the Sun

  • ecliptic coordinate system

    (n.) celestial coordinates based on the ecliptic plane

  • effective temperature

    (n.) temperature of a blackbody emitting the same radiation.

  • elliptical galaxy

    (adj./n.) a galaxy shaped like an elongated ellipsoid

  • elliptical orbit

    (adj./n.) path of celestial body around another in ellipse

  • elongation

    (n.) degree of stretching or lengthening

  • ephemeris

    (n.) table listing astronomical object positions over time

  • epoch

    (n.) specific date and time for astronomical data

  • equator

    (n.) Earth's great circle dividing northern and southern hemispheres

  • equatorial coordinate system

    (adj./n.) celestial coordinate system based on Earth's equator

  • equinoctial

    (adj.) related to equinoxes or occurring at equinoxes

  • equinox

    (n.) time when day and night are equal in length

  • escape velocity

    (n.) minimum speed to break planetary gravity

  • evolutionary track

    (adj./n.) path of a star or galaxy over time

  • exobiology

    (n.) study of life beyond Earth

  • extinction

    (n.) loss of light passing through Earth's atmosphere

  • extragalactic astronomy

    (adj./n.) study of objects outside our galaxy

  • extrasolar object

    (adj./n.) celestial body outside our solar system

  • extrasolar planet

    (adj./n.) planet orbiting a star outside the solar system

  • facula

    (n.) bright region on the Sun's surface

  • field galaxy

    (n.) galaxy not bound in a cluster, isolated

  • field of view

    (n.) observable sky area through an instrument

  • field star

    (n.) star not part of a star cluster

  • first light

    (n.) initial astronomical observation of a telescope

  • first magnitude star

    (n.) brightest star in the night sky

  • First Point of Aries

    (n.) vernal equinox point marking celestial coordinates

  • First Point of Libra

    (n.) celestial coordinate reference point in Libra

  • fixed stars

    (adj./n.) stars that appear stationary from Earth's perspective

  • flare star

    (n.) star exhibiting sudden brightness increases

  • Fulton gap

    (n.) mass range where exoplanets are rare

  • galactic anticenter

    (adj./n.) direction opposite the Galactic Center

  • galactic astronomy

    (adj./n.) study of galaxies and their structures

  • Galactic Center

    (n.) central region of the Milky Way galaxy

  • galactic coordinate system

    (adj./n.) sky coordinate system centered on the galaxy

  • galactic corona

    (adj./n.) hot, ionized gas surrounding the galaxy

  • galactic nucleus

    (adj./n.) bright, dense center of a galaxy

  • galactic period

    (adj./n.) time for a galaxy to complete an orbit

  • galactic tide

    (adj./n.) gravitational effect on objects within a galaxy

  • galactocentric distance

    (adj./n.) distance from galaxy's center

  • galaxy

    (n.) massive system of stars, gas, and dust

  • galaxy cluster

    (n.) group of multiple galaxies bound by gravity

  • galaxy group

    (n.) smaller collection of galaxies in a cluster

  • Galilean moons

    (n.) moons of Jupiter: Io, Europa, Ganymede, Callisto

  • gas giant

    (n.) large planet composed mainly of gases

  • geocenter

    (n.) center point of Earth's mass

  • geocentric

    (adj.) centered on Earth

  • geocentric zenith

    (adj./n.) point directly above observer on Earth's center

  • geometric albedo

    (adj./n.) reflectivity of a celestial body based on geometry

  • geometric position

    (adj./n.) location determined by geometric measurements

  • geostationary orbit

    (adj./n.) orbit matching Earth's rotation, stationary relative to Earth

  • geosynchronous orbit

    (adj./n.) orbit with period equal to Earth's rotation

  • giant planet

    (adj./n.) large planet like Jupiter or Saturn

  • globular cluster

    (adj./n.) spherical collection of old stars

  • gravitational collapse

    (adj./n.) contraction under gravity forming stars or structures

  • gravitational lens

    (adj./n.) mass bends light from distant objects

  • H II region

    (n.) cloud of ionized hydrogen gas

  • heliocenter

    (n.) centered on the Sun

  • heliocentric

    (adj.) centered on the Sun

  • heliopause

    (n.) boundary where solar wind ceases

  • heliosphere

    (n.) Sun's magnetic field extending into space

  • Hill sphere

    (n.) region where a body’s gravity dominates

  • horizon

    (n.) observable boundary of the sky

  • hour angle

    (n.) measure of time since last passage of a star crossing local meridian

  • hour circle

    (n.) great circle passing through celestial poles and a point

  • hybrid pulsator

    (adj./n.) star exhibiting multiple pulsation modes

  • hydrogen burning limit

    (n.) minimum mass for hydrogen fusion in star

  • hypergalaxy

    (n.) vast group of connected galaxies

  • ice giant

    (adj./n.) large planet with icy composition, e.g., Neptune

  • inclination

    (n.) angle between a body's orbit and reference plane

  • inferior planet

    (adj./n.) planet closer to the Sun than Earth

  • infrared astronomy

    (adj./n.) study of objects in infrared spectrum

  • International Astronomical Union

    (n.) organization overseeing astronomy standards

  • interstellar medium

    (adj./n.) material between stars in a galaxy

  • interstellar reddening

    (adj./n.) star light reddening caused by dust

  • invariable plane

    (adj./n.) plane containing the total angular momentum of system

  • ionosphere

    (n.) Earth's atmosphere layer ionized by solar radiation

  • irregular galaxy

    (adj./n.) galaxy without defined shape

  • irregular moon

    (adj./n.) moon with no regular pattern or orbit

  • isochrone

    (n.) curve representing stars of same age

  • Jeans instability

    (n.) cloud of gas collapses under gravity

  • Julian year

    (n.) 365.25 days in astronomical calendar

  • Kepler orbit

    (n.) orbit following Kepler's laws, elliptical shape

  • Kuiper belt

    (n.) region of small icy bodies beyond Neptune

  • Lagrangian point

    (n.) stable position in a two-body system

  • Laniakea Supercluster

    (n.) vast supercluster including the Milky Way

  • libration

    (n.) oscillation of celestial bodies like the Moon

  • limb

    (n.) edge of a celestial body's disk

  • limb darkening

    (n.) dimming near a star's limb

  • line of apsides

    (n.) line connecting closest and farthest points in orbit

  • Local Group

    (n.) galaxy collection including the Milky Way

  • luminosity

    (n.) total energy emitted by an object

  • lunar

    (adj.) relating to the Moon

  • lunar phase

    (adj./n.) Moon's visible shape over a month

  • magnetic switchback

    (adj./n.) sudden magnetic field change in solar wind

  • magnetosphere

    (n.) region around a planet influenced by magnetic field

  • magnitude

    (n.) measure of size or brightness

  • main sequence

    (n.) star phase fusing hydrogen in core

  • major axis

    (n.) longest diameter of an elliptical orbit

  • March equinox

    (n.) vernal equinox occurring in March

  • massive compact halo object

    (n.) hypothetical dark matter candidate

  • mean anomaly

    (n.) time measure in orbital mechanics

  • meridian

    (n.) imaginary line through Earth's poles

  • meridian astronomy

    (n.) study of celestial meridians

  • Messier object

    (n.) deep-sky astronomical object catalog

  • metallicity

    (n.) abundance of elements heavier than helium

  • meteor

    (n.) bright streak from atmospheric entry

  • meteor shower

    (n.) frequent meteors from same source

  • meteorite

    (n.) meteor that hits Earth's surface

  • meteoroid

    (n.) space rock in Earth's atmosphere

  • micrometeorite

    (n.) very small meteorite in atmosphere

  • micrometeoroid

    (n.) tiny space debris

  • microvariable

    (n.) small star with brightness variation

  • Milky Way

    (n.) our galaxy's luminous band in sky

  • minor axis

    (n.) shorter diameter of an ellipse

  • minor planet

    (n.) small planetary object orbiting Sun

  • molecular cloud

    (n.) gas cloud with molecules, star-forming

  • moment of inertia factor

    (n.) measure of resistance to rotation

  • Moon

    (n.) Earth's natural satellite

  • moonlet

    (n.) small moon orbiting a planet

  • moonmoon

    (n.) moon of a moon; hypothetical or minor

  • morning width

    (n.) spatial extent of morning astronomical phenomena

  • moving cluster

    (n.) stars moving together through space

  • moving group

    (n.) stars sharing common motion

  • multiverse

    (n.) theory of multiple universes

  • N galaxy

    (n.) another galaxy designation

  • nadir

    (n.) lowest point beneath observer

  • naked eye

    (n.) visible without telescope

  • natural satellite

    (n.) celestial body's companion (moon)

  • nebula

    (n.) gaseous interstellar cloud

  • neutrino

    (n.) elusive subatomic particle

  • neutron star

    (n.) dense remnant of supernova

  • New General Catalogue

    (n.) astronomical object catalog

  • night sky

    (n.) sky visible during nighttime

  • nova

    (n.) stellar explosion increasing brightness

  • nuclear star cluster

    (n.) compact star group at galaxy center

  • number density

    (n.) objects per unit volume

  • nutation

    (n.) wobble in Earth's rotation axis

  • OB association

    (n.) group of hot, massive stars

  • obliquity

    (n.) axial tilt of a planet or star

  • observable universe

    (n.) region visible from Earth

  • observation arc

    (n.) time span of observation

  • observational astronomy

    (n.) study via telescopes

  • occultation

    (n.) one celestial body blocking another

  • Oort cloud

    (n.) distant comet reservoir in space

  • opacity

    (n.) measure of light absorption

  • open cluster

    (n.) loosely bound star group

  • opposition

    (n.) planet alignment opposite Sun

  • orbit

    (n.) path of celestial object around a star

  • orbit plot

    (n.) graph representing orbital motion

  • orbital eccentricity

    (n.) eccentricity of an orbit

  • orbital elements

    (n.) parameters defining an orbit

  • orbital inclination

    (n.) tilt of orbit's plane

  • orbital mechanics

    (n.) study of orbital motion

  • orbital node

    (n.) point where orbit crosses ecliptic

  • orbital period

    (n.) time for one orbit

  • orbital plane

    (n.) flat surface containing orbit

  • orbital resonance

    (n.) gravitational locking of orbits

  • orbital speed

    (n.) velocity of an orbiting object

  • origin of longitude

    (n.) reference point for coordinates

  • orphan planet

    (n.) free-floating planetary-mass object

  • osculating orbit

    (n.) instantaneous orbital ellipse

  • outer space

    (n.) region beyond Earth's atmosphere

  • parallax

    (n.) apparent shift of nearby objects

  • parsec

    (n.) unit of distance (~3.26 light-years)

  • partial solar eclipse

    (n.) part of Sun obscured

  • peak magnitude

    (n.) brightest apparent brightness

  • periapsis

    (n.) closest point in orbit

  • perigee

    (n.) closest point of Moon to Earth

  • perihelion

    (n.) closest point of planet to Sun

  • perturbation

    (n.) deviation in orbital motion

  • phase angle

    (n.) Sun-object-observer angle

  • photometric system

    (n.) intensity measurement framework

  • photosphere

    (n.) Sun's visible surface layer

  • plane of reference

    (n.) standard plane for measurements

  • plane of the ecliptic

    (n.) Sun's apparent path

  • plane of the sky

    (n.) sky as seen from Earth

  • planemo

    (n.) celestial body capable of nuclear fusion

  • planet

    (n.) large celestial body orbiting a star

  • planetary

    (adj.) relating to planets

  • planetary body

    (n.) celestial objects like planets

  • planetary differentiation

    (n.) layer separation in planets

  • planetary nebula

    (n.) expanding gas around dying star

  • planetary science

    (n.) study of planets

  • planetary system

    (n.) star and orbiting bodies

  • planetesimal

    (n.) small building block of planets

  • planetoid

    (n.) small planetary object

  • planetology

    (n.) the study of planets

  • polar orbit

    (n.) orbit passing over Earth's poles

  • positional astronomy

    (n.) study of celestial positions

  • precession

    (n.) gradual change in a celestial body's axis orientation

  • precession of the equinoxes

    (n.) wobble causing shifting equinox points over time

  • primary

    (adj.) main celestial body in a system

  • prograde motion

    (n.) movement in the direction of rotation

  • projected separation

    (n.) apparent distance between objects in view

  • proper motion

    (n.) star's movement across the sky over time

  • proplyd

    (n.) protoplanetary disk around a young star

  • protoplanet

    (n.) building block of a planet

  • protoplanetary disk

    (n.) rotating disk of material around a young star

  • protostar

    (n.) early stage star still gathering mass

  • pulsar

    (n.) highly magnetized rotating neutron star emitting beams

  • quadratic field strength

    (n.) variation proportional to square of position

  • quadrature

    (n.) 90-degree phase angle between celestial objects

  • quasar

    (n.) extremely luminous distant active galaxy nucleus

  • radial velocity

    (n.) speed toward or away from observer

  • radio astronomy

    (n.) study of celestial objects via radio waves

  • radio source

    (n.) emitting object detectable in radio wavelengths

  • redshift

    (n.) shift toward longer wavelengths indicating recession

  • reference plane

    (n.) baseline for celestial coordinate measurement

  • regular moon

    (n.) moon cycle with predictable phases

  • relativistic jet

    (n.) high-speed jet from a galaxy or black hole

  • retrograde motion

    (n.) planet appears to move backward in sky

  • revolution period

    (n.) time taken for one orbit

  • right ascension

    (n.) celestial longitude coordinate

  • ring system

    (n.) set of rings surrounding a planet

  • Roche limit

    (n.) closest distance a moon can approach without breakup

  • rogue planet

    (n.) free-floating planet not orbiting a star

  • Rosseland optical depth

    (n.) measure of transparency in stellar atmospheres

  • rotation period

    (n.) time for an object to complete one spin

  • rotational modulation

    (n.) brightness change due to rotation

  • satellite galaxy

    (n.) smaller galaxy orbiting a larger one

  • scattered disc

    (n.) distant icy body region beyond Neptune

  • scintillation

    (n.) rapid fluctuation of star brightness

  • secular

    (adj.) long-term gradual change

  • secular motion

    (n.) slow, continuous movement of celestial objects

  • selenocentric

    (adj.) centered around the Sun

  • September equinox

    (n.) event marking start of fall in northern hemisphere

  • sidereal day

    (n.) Earth's rotation period relative to stars

  • sidereal period

    (n.) time for an object to complete one orbit relative to stars

  • sidereal time

    (n.) time based on Earth's rotation relative to stars

  • sidereal year

    (n.) Earth's orbit period relative to stars

  • sky

    (n.) expanse of space visible from Earth's surface

  • small Solar System body

    (n.) minor celestial object like asteroid or comet

  • solar day

    (n.) time from one sunrise to the next

  • solar eclipse

    (n.) Moon blocks Sun from viewpoint on Earth

  • solar facula

    (n.) bright area on the Sun's surface

  • solar flare

    (n.) intense burst of solar radiation

  • solar granule

    (n.) small convective cell on the Sun's surface

  • solar jet

    (n.) narrow stream of plasma from the Sun

  • solar mass

    (n.) mass of the Sun used as a standard unit

  • solar moss

    (n.) bright, fuzzy features on the Sun's surface

  • solar prominence

    (n.) large, bright cloud of plasma in Sun's atmosphere

  • solar radius

    (n.) distance from Sun's center to surface

  • solar spicule

    (n.) jet of material from Sun's surface

  • solar storm

    (n.) disturbance caused by solar activity

  • Solar System

    (n.) Sun and orbiting celestial bodies

  • solar time

    (n.) time based on Sun's position

  • solar wind

    (n.) stream of charged particles from Sun

  • solstice

    (n.) longest or shortest day of the year

  • spectral classification

    (n.) categorization of stars by spectrum

  • spectroscopic binary

    (n.) star pair detected via spectra shifts

  • spectroscopy

    (n.) study of light spectra from objects

  • speed of light

    (n.) maximum speed of electromagnetic waves

  • spherical astronomy

    (n.) study of celestial spheres and coordinates

  • spiral galaxy

    (n.) galaxy with spiral arms structure

  • standard gravity

    (n.) acceleration due to gravity at Earth's surface

  • star

    (n.) luminous celestial body made of hot gases

  • star catalogue

    (n.) list of recorded stars and data

  • star cluster

    (n.) group of stars gravitationally bound

  • star system

    (n.) star and its planets or companions

  • starburst galaxy

    (n.) galaxy with exceptionally high star formation

  • starfield

    (n.) visible distribution of stars in the sky

  • stellar

    (adj.) related to stars

  • stellar atmosphere

    (n.) outer layer of a star

  • stellar classification

    (n.) categorizing stars by spectra and brightness

  • stellar designation

    (n.) official naming of stars

  • stellar dynamics

    (n.) study of motions of stars within systems

  • stellar envelope

    (n.) outer layer surrounding a star

  • stellar evolution

    (n.) changes a star undergoes over time

  • stellar evolution model

    (n.) theoretical framework of star development

  • stellar magnetic field

    (n.) magnetic field associated with a star

  • stellar parallax

    (n.) apparent shift due to Earth's movement

  • stellar remnant

    (n.) leftover core after a star's death

  • submillimetre astronomy

    (n.) study of celestial objects at submm wavelengths

  • subsatellite

    (n.) secondary satellite orbiting a satellite

  • substellar object

    (n.) object not massive enough to be star

  • Sun

    (n.) closest star at galaxy's center of our solar system

  • supercluster

    (n.) large group of galaxy clusters

  • superior planet

    (n.) planets beyond Earth's orbit

  • supermassive black hole

    (n.) extremely large black hole at galaxy's core

  • supernova

    (n.) massive stellar explosion

  • surface gravity

    (n.) gravity experienced at a celestial body's surface

  • synchronous orbit

    (n.) orbit aligning with a body's rotation

  • synodic day

    (n.) time between similar moon phases

  • synodic period

    (n.) time between consecutive alignments

  • synodic time

    (n.) period between recurring celestial configurations

  • syzygy

    (n.) alignment of three celestial bodies in a straight line

  • tangential velocity

    (n. phr.) speed moving along a circular path

  • telescope

    (n.) instrument for observing distant objects

  • telluric star

    (n. phr.) star observed through Earth's atmosphere

  • termination shock

    (n. phr.) boundary where solar wind slows abruptly

  • terminator

    (n.) line dividing daylight and darkness

  • theoretical astronomy

    (n. phr.) theoretical study of celestial phenomena

  • thick disk population

    (n. phr.) stars in a galaxy's extended disk

  • thin disk population

    (n. phr.) stars in a galaxy's flat disk

  • tidal braking

    (n. phr.) slowing rotation via gravitational forces

  • tidal force

    (n. phr.) gravity stretching objects due to nearby masses

  • tidal locking

    (n. phr.) one object always faces its partner

  • tidal stream

    (n. phr.) star trail from gravitational stripping

  • tilt erosion

    (n. phr.) loss of axial tilt over time

  • topocentric

    (adj.) perspective from Earth's surface

  • total solar eclipse

    (n. phr.) Moon blocks Sun completely

  • transit

    (n.) object passes in front of a star

  • trojan

    (adj./n.) asteroid sharing orbit with a planet

  • tropical year

    (n. phr.) earth's orbit-based year length

  • true anomaly

    (n. phr.) actual position of orbiting body

  • twilight

    (n.) dusk or dawn light period

  • UBV photometric system

    (n. phr.) astronomical color measurement system

  • universe

    (n.) all existing matter and energy

  • variable star

    (n. phr.) star with changing brightness

  • velocity dispersion

    (n. phr.) spread of velocities in a system

  • Virgo Supercluster

    (n. phr.) large galaxy cluster including Milky Way

  • white dwarf

    (n. phr.) remnant core of a dead star

  • XBONG

    (n.) X-ray bright optically normal galaxy

  • zenith

    (n.) highest point in the sky directly overhead

  • zodiac

    (n.) constellation belt along ecliptic

  • zodiacal light

    (n. phr.) faint glow from dust in solar system

  • Zone of Avoidance

    (n. phr.) galactic plane obscured region