Galaxy Explorer’s A to Z Dictionary of Space Terms & Dictionary
As the Galaxy Explorer, there will be times when I need to use specific space-related terms while describing what I see. For example, when I say “Cosmic Microwave Background Radiation,” it might sound confusing. That’s why I’ve prepared this space terminology dictionary for you. Plus, by learning these terms, you can even impress your friends—but try not to act like a know-it-all!
All the space terms you need to know, from A to Z:
A B C D E F G H I J K L M N O P R S T U V Y Z W-Q
A
Aberration: An apparent change in the positions of stars.
Accretion Disk: A structure formed by material orbiting and accumulating around a massive body.
Air Pollution: The contamination of the indoor or outdoor environment by any chemical, physical, or biological agent that alters the natural properties of the atmosphere.
Albedo: The ability of a surface in space to reflect incident energy.
Alcyoneus Galaxy: The largest galaxy in the universe, with a diameter of 16 million light-years.
Alien: A life form originating outside Earth.
Andromeda Galaxy: The galaxy known as M31, located 2.2 million light-years from the Milky Way.
Annular Solar Eclipse: A solar eclipse that occurs when the Moon is too far from Earth to fully cover the Sun, allowing a ring of sunlight to be seen around the Moon’s edge.
Anthropogenic: A term used to describe damage caused by human activity.
Aphelion: The point in a planet’s or celestial body’s orbit where it is farthest from the Sun.
Aphelion: The point in an object’s orbit around the Sun where it is farthest from the Sun.
Apollo Programs: Manned and unmanned lunar missions conducted by NASA.
Asteroid Belt: The region between the orbits of Mars and Jupiter where most asteroids are found.
Asteroid: Small, rocky celestial bodies.
Astrobiology: The scientific field that studies the origin and evolution of life in the universe.
Astronaut: Interstellar travelers on missions beyond Earth. E.g., Galaxy Explorer.
Astronomical Transit: The phenomenon where an observer sees an object as a black dot as it passes in front of a large celestial body.
Astronomical Unit (AU): The average distance between Earth and the Sun. 1 AU = 149,600,000,000 km
Astronomical Unit (AU): The distance of 149.6 million km between Earth and the Sun. It is used to express vast distances in the universe.
Astronomy: The scientific field that observes and explains the movements, origins, and physical and chemical properties of celestial objects.
Astrosismology: A technique used to determine a star’s internal structure, composition, and age by observing its natural oscillations.
Atmosphere: The layer surrounding Earth and some planets, primarily composed of gases and vapors.
Atmospheric Cycle: The cycle of air and water in the atmosphere.
Atmospheric Escape: The thinning or loss of a planet’s atmosphere.
Atmospheric Humidity: The amount of water vapor carried in the air.
Atmospheric Phenomena: Weather conditions resulting from physical changes in Earth’s atmosphere. (e.g., Rain, Hurricane, Snow)
Atmospheric Pollution: The contamination of the atmosphere’s internal or external environment. Also known as air pollution.
Atmospheric Pressure Units: Hectopascals (hPa), millibars (mbar), or inches of mercury (inHg).
Atmospheric Pressure: The pressure exerted by the air.
Atmospheric Refraction: The deviation of light from a straight path as it passes through the atmosphere and the resulting change in its frequency.
Axial Tilt: The angle between a celestial body’s rotational axis and its orbital axis.
Axis: A fixed line, ray, or line segment used to measure direction, distance, angle, orientation, position, or motion in space.
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B
Baily’s Beads: A ring of light that appears along the edge of the Moon during a solar eclipse.
Barometer: A device used to measure atmospheric pressure.
Barometer: A mercury-filled tube used to measure atmospheric pressure.
Barred Spiral Galaxy: Spiral galaxies with a central bar. (e.g., the Milky Way Galaxy)
BD+17°3248: The second-oldest star in the universe.
Big Bang: The event believed to have triggered the beginning of the universe.
Big Bounce: A theory proposing that after the universe expands sufficiently, it will begin to contract.
Big Collapse: A theory proposing that the universe will collapse in on itself.
Big Rip: A theory proposing that the power of dark energy will increase and completely tear the universe apart.
Binary Merger: The collision of two galaxies.
Binary Planets: Planets that orbit two stars.
Binary Planets: Two planets that orbit each other and share the same orbit.
Binary Star System: A system formed by two stars orbiting each other.
Binary Star: Two stars orbiting each other.
Black Body: A hypothetical object that absorbs all incident light of all wavelengths without reflecting any of it, and then re-emits it. The radiation it emits depends solely on its temperature.
Black Hole: The densest form of matter believed to exist in the universe. Since the escape velocity from a black hole is greater than the speed of light, not even light can escape from it.
Blanet: Planets orbiting around black holes.
Blue Dwarf: Theoretical stars that white dwarfs are predicted to become after cooling.
Blue Galaxy: Galaxies actively forming stars, characterized by high brightness, temperature, and mass.
Boötes Void: The largest known cosmic void. See: Cosmic void.
BOSS Great Wall: An observational study conducted to examine the distribution of large galaxy groups and galaxies relative to one another.
Brown Dwarf (Failed Star): Brown celestial objects that are too small to sustain nuclear fusion.
C
Canopus: The second brightest star in the sky.
Carbon Planets: Theoretical planets with atmospheres containing more carbon than oxygen.
Cassini Spacecraft: A spacecraft launched in 1997 as a collaboration between NASA, ESA, and ASI, which operated until 2017 to study Saturn.
Celestial Object: Any object in space
Ceres: A dwarf planet located between Mars and Jupiter.
Chandrasekhar Limit: The maximum mass limit for white dwarf stars.
Cherenkov Radiation: Radiation produced by a particle moving faster than the speed of light in the surrounding medium.
Chthonian Planets: Gas giants devoid of hydrogen and helium.
Collision: The collision of two or more celestial bodies due to gravitational attraction or external forces.
Comet: A celestial object composed of ice, dust, and rock, appearing to have a tail due to the gas it emits as it vaporizes.
Convection Zone: The region in stars where energy is transported from the radiation zone to the surface, releasing light and other forms of energy. It is also the region responsible for creating stellar flares and sunspots.
Core-less Planets: Planets that, theoretically, lack a core.
Core: The densest and hottest point at the center of a celestial body.
Corona: The gaseous envelope of stars composed of plasma.
Coronal Mass Ejection (CME): A solar eruption in the Sun’s corona that expels plasma into space.
Cosmic Microwave Background (CMB): Residual heat left over from the Big Bang between celestial objects. The oldest light in the universe.
Cosmic Rays: Particles moving through space at very high energies.
Cosmic Void: Regions in the universe where matter and galaxies are sparse.
Cosmogony: The science that studies the creation of the universe.
Cosmology: The science that studies the structure and evolution of the universe.
Cosmos: The universe.
Cryosphere: The name given to the frozen ground that covers a planet globally.
Curiosity Rover: A rover sent to Mars by NASA in 2012.
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D
Dark Energy: A mysterious energy that accelerates the expansion of the observable universe and is still not fully understood.
Dark Matter: Matter that does not emit electromagnetic radiation and is detected only through gravitational effects, but whose nature remains unknown.
Dark Matter: The most fundamental structure required for the formation of galaxies, formed when energy waves succumbed to their own gravity after the Big Bang.
Dark Star: A star composed of dark matter.
Deuterium (Heavy Hydrogen): One of the stable isotopes of hydrogen. Used in nuclear fusion.
Doppler Effect: The change in the wavelength or frequency of light emitted from a source when the source is moving away from or toward the observer.
Dry Merger: The merger of galaxies with low gas content.
Dwarf Galaxy: Small galaxies composed of 1,000 to several billion stars.
Dwarf Planet: Planet-like celestial bodies lacking sufficient gravitational pull to clear their orbital path.
Dyson Sphere: A Type 2 civilization structure that completely surrounds a star and captures its energy.
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E
Earth-like Planets: Planets similar in size to Earth that meet the conditions for a habitable zone.
Earth: The planet in the Solar System where humanity lives.
EBLM J0555-57Ab: The smallest star in the universe.
Eccentric Jupiter: A gas giant with an elliptical orbit that is not centered on the planet.
Electromagnetic spectrum: The spectrum formed by electromagnetic radiation across all wavelengths.
Escape Velocity: The speed required for an object to completely escape the gravitational field of another object.
Event Horizon: The region around a black hole from which neither light nor matter can escape.
Exosphere: The upper boundary of Earth’s atmosphere.
Extragalactic Planets: All planets located outside the Milky Way Galaxy.
Extremely Dispersed Galaxy: Galaxies with low gas density, low luminosity, and old stars.
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F
Fermi Bubbles: Large, energy-rich bubbles whose exact nature is unknown.
Fermi Gamma-ray Space Telescope: A telescope used to detect gamma rays.
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G
Galaxy: An independent island in space composed of clusters of millions of stars, nebulae, and gas clouds.
Gamma Rays: Radiation composed of photons with shorter wavelengths and higher energy than X-rays.
Ganymede: Jupiter’s largest moon.
Gas Dwarf: Gaseous planets with less mass than Neptune.
Gas Giant: A planet composed primarily of gas.
General Relativity: A physical theory developed by Albert Einstein regarding the curvature of spacetime caused by forces such as gravity.
Geodesy: The branch of science concerned with the shape and dimensions of the Earth.
Geoid: The shape of the Earth where the gravitational force is constant at every point and is in perfect equilibrium with the Earth’s rotational force.
GLASS-z12: The oldest galaxy in the universe.
GN-z11: The most distant galaxy at the edge of the observable universe.
Goldilocks Planets: Planets that meet the conditions of the habitable zone.
Gravitational Attraction: The force by which planets or objects pull other objects toward their center.
Gravitational Force: The force exerted by objects with mass. See: Gravitational force
Gravitational Lensing: The bending and magnification of light from an object behind a massive object.
Gravitational Lock: Synchronous rotation. A situation where an astronomical object in orbit always faces the same side toward the object it orbits.
Gravity: The acceleration exerted by a planet on objects at its surface.
Great Filter Theory: A theory suggesting that there are “filters” that prevent the formation and survival of intelligent life.
Great Red Spot: A storm that has been raging on Jupiter for centuries.
Greenhouse Effect: The trapping of energy by the atmosphere, maintaining surface temperature.
Gustave Hermite: The person who invented the weather balloon to study the atmosphere.
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H
Habitable Zone: The orbital region around a star where conditions may support life on a planet.
Halley's Comet: A comet observed once every 76 years.
HD 1 Galaxy: The farthest galaxy from Earth, located 13.463 billion light-years away.
HD 98800: A multiple star system consisting of four distinct stars.
Heat Death: The idea that as the universe expands, it will become a colder place and eventually reach a state of entropic equilibrium.
Hectopascal (hPa): One of the units used to measure atmospheric pressure.
Helium Planets: Planets with a higher proportion of helium in their atmospheres.
Henry Tracey Coxwell: The person who, along with James Glaisher, made history by reaching the stratosphere in a hot-air balloon.
Hercules-Coma Berenices Great Wall: The largest structure in the universe.
High Pressure: A condition where the density of gas in the atmosphere is relatively higher.
Hoag’s Object: A round galaxy with an outer ring.
Homosphere: A group of atmospheric layers comprising the troposphere, stratosphere, mesosphere, and the lower part of the thermosphere.
Hot Jupiters: Jupiter-like planets that orbit very close to their stars.
Hot Neptunes: Planets similar to Neptune or Uranus but with higher temperatures.
Hubble Space Telescope: A space telescope used to study galaxies, stars, and other astronomical objects in deep space.
Hybrid Solar Eclipse: A combination of a total and an annular solar eclipse. It is the rarest type of solar eclipse.
Hydrogen Fusion: A fusion process that converts hydrogen (protons) into heavier elements.
Hydrogen Planets: Planets with hydrogen atmospheres that are hot and covered in oceans.
Hypernova: A stellar death event hundreds of times more powerful than a supernova.
Hypothetical Planets: Planets proposed theoretically, most of which have not been observed.
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I
Icarus: The farthest star.
Ice Giants: Cold planets composed of gases that lack a solid surface.
Ice Planets: Cold planets with a cold, frozen cryosphere.
Inch of Mercury (inHg): One of the units used to define atmospheric pressure.
Inner and Outer Group Planets: A classification of planets based on whether they lie within (inner group) or outside (outer group) the orbit of another planet.
Inner Planets: Terrestrial planets that are close to their star. The distance between them is shorter than that of the outer planets.
Innermost stable circular orbit: The complete orbits of two black holes before they merge.
Interferometry: Observing a celestial object from different positions to obtain more detailed and high-quality results.
Intergalactic Stars: Stars in the universe that are not affiliated with any particular galaxy.
Io: Jupiter’s innermost large moon and the most volcanically active body in the Solar System.
Ionosphere: A layer in the Earth’s atmosphere where atoms and molecules are ionized by solar radiation and cosmic rays.
Iron Planets: Planets with abundant iron in their cores and typically lacking a mantle.
Irregular Galaxy: Galaxies that lack a specific shape and are smaller compared to other galaxies.
J
J1407b: The planet with the most rings in the universe, boasting 37 rings.
James Glaisher: The person who, along with Henry Tracey Coxwell, made history by reaching the stratosphere in a hot-air balloon.
James Webb Telescope: A space telescope launched into space and designed specifically to conduct observations in the infrared wavelength range.
Joseph-Michel and Jacques-Etienne Montgolfier: The French brothers who invented the hot-air balloon in 1783.
Jupiter: The largest planet in the solar system.
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K
Kardashev Scale: A scale classifying the development of civilizations into four categories.
Karl Scheele: The first person to isolate oxygen.
Kepler-70b: The hottest planet in the universe, with a temperature of 7,027°C.
Kessler Syndrome: The collision of satellites in Earth’s orbit with one another or with other space debris, leading to an increase in space debris.
Kilonova: An explosion resulting from the collision of two neutron stars.
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L
Lagrange Points: Specific regions in space where the gravitational forces of two celestial bodies balance with the centrifugal force.
Laika: The first dog sent into space.
Large Magellanic Cloud: The dwarf galaxy nearest to the Milky Way.
Late Heavy Bombardment (Moon Storm): A period believed to have occurred between 4.1 and 3.8 billion years ago, during which asteroids and meteors rained down on the inner planets of the Solar System.
Lava Planets: Planets whose surfaces are mostly or entirely covered with lava.
Lenticular Galaxy: Galaxies without spiral arms and possessing a large central disk.
Lepton: One of the fundamental particles and a building block of matter. The most well-known lepton is the electron, and there are six types in total.
Light-Year: The distance light travels in one year. 9,000,000,000,000 km.
Lithosphere: The outermost layer of the Earth's crust, also where fault lines are located and earthquakes occur.
Low Pressure: A lower density of gas in the air.
Lower Meridian: The portion of the meridian lying below the horizon.
Lunar Eclipse: A natural phenomenon that occurs when the Moon passes behind the Earth and enters the Earth’s shadow.
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M
M-Theory: A theory that unifies the five string theories and proposes that our 3-dimensional universe exists within 11 dimensions.
Magnetar: Neutron stars that emit intense X-rays and gamma rays.
Magnitude: A measure of the brightness of a star or other observed astronomical object.
Main-Sequence Stars: These stars make up 90% of the universe. They are stars that convert hydrogen into helium.
Mars (The Red Planet): The fourth planet in the Solar System.
Mercury: The smallest planet in the Solar System.
Merger: The collision of two large galaxies of similar size, resulting in the formation of a larger galaxy.
Meteor Crater: A crater formed when a meteor impacts a surface.
Meteor: Each of the rocky particles traveling between planets.
Meteorite: Any type of rock that falls from the sky to Earth.
Meteorology: The science that studies the atmosphere and weather phenomena.
Methuselah: The oldest known star in the universe.
Milky Way Galaxy: The galaxy that contains the Solar System.
Millibar (mbar): A unit used to measure atmospheric pressure.
Millisecond Pulsar: Pulsars with rotation periods of less than 10 milliseconds.
Minor Planet: Asteroid.
Mixed Merger: The merger of galaxies with low and high gas ratios.
Moon: Earth’s only natural satellite.
Morgan-Keenan (MK) Classification: A system that classifies stars in the universe using the letters A through Y.
Multiple Merger: The collision of three or more galaxies.
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N
NASA: National Aeronautics and Space Administration (United States).
Nebula: A cloud composed of interstellar gas and dust.
Nebula: A cloud of gas and dust in space.
Neptune: The windiest planet in the Solar System.
Neutrino Detectors: Instruments used to detect neutrinos produced in stellar nuclear reactions and to understand energy production in stars.
Neutrino: A nearly massless particle with no electric charge that can pass through matter almost undisturbed, moving close to the speed of light.
Neutron Star: The collapsed core of a star composed almost entirely of neutrons.
Non-rising star: A star that does not rise above the horizon during its daily motion.
Non-Setting Star: A star that does not dip below the horizon during its daily motion.
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O
Observable Universe: The portion of space from which light or other electromagnetic radiation can reach us.
Oh-My-God (OMG) Particle: A cosmic ray moving just 0.000000000000000000000051% slower than the speed of light.
Oort Cloud: A shell of icy objects surrounding the Solar System.
Orbit: The orbital motion of an object around a point or another object.
Orbit: The path traced by a celestial body as it moves through space.
Oumuamua: The first known celestial object to enter the Solar System from interstellar space.
Outer Planets: Gas giants located farther from their star, with significant distances between them.
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P
Panspermia Theory: The theory that life can spread through space, suggesting microorganisms are transported between planets via cosmic carriers.
Parallax Method: A technique to calculate the distance of a star based on angular shift.
Partial Lunar Eclipse: An eclipse in which only a portion of the Moon enters Earth's shadow, making it appear as if a “bite” has been taken out.
Partial Solar Eclipse: A solar eclipse caused by the Moon covering only part of the Sun, due to Earth, Moon, and Sun not being perfectly aligned.
Penumbral Lunar Eclipse: A lunar eclipse where a faint shadow falls on the Moon’s surface, making it difficult to observe.
Perihelion: The point in a planet’s or celestial body’s orbit where it is closest to the Sun.
Phase: The position of each point within a cycle in a repetitive event.
Phases of the Moon: The illuminated surfaces of the Moon visible from Earth as it reflects sunlight.
Photometry: A technique used to measure the brightness of stars.
Photon Sphere: The boundary of a black hole. A sphere formed when photons begin to spin continuously due to extremely high gravitational pull.
Photon: A particle of light or other electromagnetic radiation.
Photosphere: The name given to the surface of a star. Sunspots are visible in this region.
Planet: The collective term for celestial bodies that orbit a star and reflect the light they receive from it.
Planetary Boundary Layer (PBL): The lowest part of Earth’s atmosphere, extending from the Earth’s surface to an altitude of approximately 100 to 2,000 meters.
Plasma: A gas in which atoms are partially or fully ionized and compressed under high pressure.
Polaris (North Star): The star that consistently indicates the direction of true north in the sky.
Protoplanets: The early formation centers of planets.
Pulsar Planets: The name given to planets orbiting pulsars.
Pulsar: Neutron stars that rotate rapidly, emit radio waves into space, and possess a strong magnetic field.
R
Radiation Zone: The region that carries energy (photons) and surrounds the core.
Radio Galaxy: Galaxies that emit large amounts of radio waves due to strong magnetic fields.
Radio Telescope: A telescope designed to observe the radio emissions from celestial objects.
Radio Waves: Electromagnetic waves with wavelengths greater than 1 cm.
Rare Earth Hypothesis: A theory that argues planets like Earth are rare, making the development of intelligent life uncommon.
Red Galaxy: Galaxies that are not actively forming stars, characterized by low luminosity, mass, and temperature.
Reddening: The phenomenon where light appears redder than it actually is due to the greater absorption of blue wavelengths as it passes through a medium.
Relativistic Radiation: The vapor trail left behind a body as it is pulled into a black hole.
Richard Assmann: Scientist who, along with Teisserenc de Bort, discovered the stratosphere in 1902 and also invented rubber balloons.
Ring Galaxy: A galaxy formed by objects orbiting in a ring-shaped pattern around a partially luminous center.
Rogue Black Hole: Black holes that roam freely through space.
Rogue Planet: A planet without a host star, wandering through space (also called orphan, free-floating, interstellar, nomad, or starless planet).
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S
Sand Planets: Planets resembling Earth’s deserts, with most of their surface consisting of such terrain.
Saros: The Saros cycle tracks the phases of the Moon and lasts 18 years, 11 hours, and 8 minutes.
Satellite: 1. Celestial bodies orbiting planets. 2. Spacecraft orbiting for data collection and communication.
Saturn: The second-largest planet in the Solar System.
Schwarzschild Black Hole: A black hole with no angular momentum or electric charge.
Segue 2: The smallest known galaxy in the universe.
Seismic Wave: Energy traveling in waves through the Earth caused by earthquakes, volcanic eruptions, landslides, or large explosions.
Self-Destruction Hypothesis: A theory proposing that civilizations in the universe destroy one another.
Silicate Planets: Planets with silicate-based rocky crusts and metallic cores.
Singularity: The center of a black hole, where gravity is infinite and the laws of physics break down.
Sirius (Dog Star): The brightest star visible in the night sky.
Small Magellanic Cloud: A dwarf galaxy neighboring the Milky Way.
Small Merger: A large galaxy swallowing a small galaxy.
Solar Eclipse Glasses: Specially filtered glasses used to view a solar eclipse.
Solar Eclipse: An astronomical event in which the Moon passes between the Earth and the Sun, completely or partially blocking the Sun.
Solar System: A term referring to the system comprising the Sun and the eight planets, including Earth, that orbit it.
Solid Vacuum: An area with very few atoms or molecules and extremely low pressure.
Space Shuttle: A reusable spacecraft used to transport astronauts and cargo to space.
Space Station: A spacecraft placed in orbit for astronauts to conduct research and observations.
Space Telescope: An instrument used to observe celestial events or radiation from space.
Space: A vast, vacuum-filled region believed to contain billions of celestial objects.
Spectroscopy: A technique used to separate starlight into its component colors.
Speed of Light: The speed of light in a vacuum. 1,080,000,000 km/h.
Spiral Galaxy: SA and SAB class galaxies with spiral arms resembling a wheel.
Star: A celestial body that emits its own light, usually producing energy through nuclear reactions of elements like hydrogen and helium.
Starburst Galaxy: Galaxies forming stars at exceptionally high rates, often due to mergers or collisions with other galaxies.
Steady-State Theory: A theory proposing that the universe has no beginning.
Stellar Scintillation: The twinkling of starlight as it passes through Earth’s atmosphere.
Stephenson 2-18: The largest known star in the universe.
Strange Radio Circles: Bright radio signals appearing in circular or ring-shaped patterns.
Stratosphere: The layer of the atmosphere containing ozone, which absorbs and distributes ultraviolet radiation from the Sun.
Sun: The star at the center of the solar system.
Super-Earths: Planets larger than Earth in size and mass (not necessarily habitable).
Supernova: The violent explosion of a massive star that has exhausted its energy.
Swift J1818.0-1607: The youngest known star in the universe.
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T
Tabby’s Star: A star thought to be surrounded by a Dyson sphere.
Teisserenc de Bort: Scientist who, along with Richard Assmann, discovered the stratosphere in 1902.
Terminator Line: The line on a celestial body separating its illuminated day side from the dark night side; the line where sunrise and sunset occur.
The Great Attractor: A force believed to pull everything in the universe toward itself, the nature of which is not fully understood.
Thermosphere: The atmospheric layer where auroras occur and artificial satellites orbit.
Thorne–Żytkow Object: A theoretical star formed when a neutron star is engulfed by a red supergiant.
Tidal Force: The gravitational force exerted by one object on another.
Tide: The phenomenon in large bodies of water where the water rises and then falls below the normal level six hours later.
TON 618: The largest known quasar in the universe.
Total Lunar Eclipse: Occurs when the Moon enters Earth’s umbra (full shadow), appearing red or coppery due to sunlight refracted through Earth’s atmosphere.
Total Solar Eclipse: Occurs when the Moon completely blocks the Sun as seen from Earth.
Triple Star System: A system consisting of two stars orbiting each other with a third star orbiting around them.
Troposphere: The atmospheric layer where weather occurs on Earth.
Tully-Fisher Relation: A method for determining the distance to spiral galaxies based on their rotation speed and total luminosity.
Type I Civilization: A civilization that harnesses the energy of its home planet (e.g., humans).
Type II Civilization: A civilization capable of harnessing the energy of its star.
Type III Civilization: A civilization capable of harnessing the energy of its entire galaxy.
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U
Umbra: The region where a celestial body casts a full shadow on another body.
Uranus: The coldest planet in the Solar System.
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V
Vacuum Decay: A theory describing the transition from the universe’s current vacuum state to a lower-energy vacuum state.
Vampire Star: A star that siphons hydrogen and plasma from a neighboring star.
Van Allen Belts: Protective layers around planets formed by magnetism that block harmful radiation from stars.
Variable Star: A star whose brightness changes over time.
Venus: The hottest planet in the Solar System.
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Y
Yerkes Spectral Classification: A system that classifies stars based on their luminosity.
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Z
Zodiac: The belt of constellations used in astrology.
Zoo Hypothesis: A theory proposing that extraterrestrial beings are aware of humans but have chosen not to make contact.
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W - Q
Water Worlds: Planets that contain significant amounts of water on or beneath their surfaces.
Wet Merger: The merger of galaxies with similar gas content.
Wet Merger: The merger of gas-rich galaxies.
White Dwarf: A small, extremely dense, collapsed star that is gradually cooling.
White Hole: A cosmic object, proven to exist, that repels light and matter rather than pulling it in, unlike a black hole.
Wormhole: A theoretical tunnel connecting one point in space to another.
Wow! Signal: A radio signal detected in 1977 with an unknown source.
Quasar: A bright, star-like radio source that derives its power from supermassive black holes.
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As a Galaxy Explorer, I’m constantly learning new space terms every day, so I’ll keep updating this glossary for you regularly!