This list covers 44 astronomy words, running alphabetically from “L Dwarf” to “Lyrid Meteor Shower.” These entries span cool failed stars, distant galaxies, lunar features, and orbital phenomena, giving you a broad snapshot of how astronomers describe the objects and events they study. Whether you’re prepping for a class, writing about space, or just curious about the night sky, this list gives you quick, reliable definitions to work from.
Astronomy words are the specialized terms scientists and stargazers use to describe celestial objects, cosmic events, and the tools used to study them. Some carry surprising history, like the light-year, which measures distance rather than time even though its name suggests otherwise. Others, like the Lyrid meteor shower, have been observed by skywatchers for over 2,700 years.
Below you’ll find the table with Word, Definition, and Description.
Word: This column lists the astronomy term itself, giving you the exact name used by scientists and skywatchers alike.
Definition: This column gives you a short, plain explanation of what the term means, so you can grasp it at a glance.
Description: This column expands on the definition with extra context, helping you understand why the term matters and how it’s used.
Astronomy words
| Word | Definition |
|---|---|
| L Dwarf | A spectral class of cool, low-mass stars and brown dwarfs |
| Lacerta | A small, faint northern constellation representing a lizard |
| Lagoon Nebula | A large emission nebula and star-forming region in Sagittarius |
| Lagrangian Point | A location where gravitational forces balance, letting an object stay fixed relative to two bodies |
| Lambda-CDM Model | The standard cosmological model of the universe’s structure and expansion |
| Laniakea Supercluster | The vast supercluster of galaxies containing the Milky Way |
| Large Magellanic Cloud | A dwarf galaxy orbiting the Milky Way |
| Lava Tube | An underground tunnel formed by flowing volcanic lava |
| Leap Second | An extra second occasionally added to clocks to match Earth’s rotation |
| Leo | A zodiac constellation representing a lion |
| Leo Minor | A small, faint constellation north of Leo |
| Lepus | A constellation representing a hare, south of Orion |
| Libra | A zodiac constellation representing scales |
| Libration | The apparent wobble of the Moon as seen from Earth |
| Light Curve | A graph showing how an object’s brightness changes over time |
| Light Pollution | Excess artificial light that obscures the night sky |
| Light-Year | The distance light travels in one year, about 9.46 trillion kilometers |
| Limb | The visible edge of a celestial body’s disk |
| Line of Nodes | The line where two orbital planes intersect |
| Local Arm | The minor spiral arm of the Milky Way containing our Sun |
| Local Bubble | A cavity of thin, hot gas surrounding our solar system |
| Local Group | The cluster of galaxies that includes the Milky Way |
| Local Sidereal Time | Time measured by Earth’s rotation relative to the stars rather than the Sun |
| Local Void | A vast, nearly empty region of space near the Local Group |
| Long-Period Comet | A comet that takes more than 200 years to orbit the Sun |
| Look-back Time | How far in the past we see an object because of light’s travel time |
| Low Earth Orbit | An orbit around Earth at a relatively low altitude, roughly below 2,000 kilometers |
| Luminosity | The total amount of energy a star radiates per second |
| Luminosity Class | A classification describing a star’s size and evolutionary stage |
| Luminosity Function | A statistical description of how many objects exist at each brightness level |
| Luminous Blue Variable | A rare, extremely massive and unstable type of star |
| Lunar Eclipse | When Earth’s shadow falls on the Moon |
| Lunar Highlands | The light-colored, heavily cratered mountainous regions of the Moon |
| Lunar Maria | The large, dark, flat plains on the Moon’s surface |
| Lunar Meteorite | A rock from the Moon that has landed on Earth |
| Lunar Month | The time it takes the Moon to complete a full cycle of phases |
| Lunar Occultation | When the Moon passes in front of a star or planet, hiding it from view |
| Lunar Phase | The changing illuminated shape of the Moon as seen from Earth |
| Lunar Regolith | The loose, dusty layer of debris covering the Moon’s surface |
| Lunar Terminator | The moving line dividing the Moon’s day and night sides |
| Lyman-Alpha Line | A specific wavelength of light emitted by hydrogen atoms |
| Lyman-Break Galaxy | A distant galaxy identified by a gap in its light spectrum |
| Lyra | A small constellation representing a lyre, home to the star Vega |
| Lyrid Meteor Shower | An annual meteor shower appearing to radiate from the constellation Lyra |
Descriptions
L Dwarf
Cooler and dimmer than typical stars, L dwarfs glow mostly in infrared light and sit on the boundary between true stars and failed “brown dwarf” stars that never ignited full fusion.
Lacerta
Wedged between Cygnus and Andromeda, Lacerta is a dim zigzag of stars with no bright standouts, mostly notable for hosting occasional novae.
Lagoon Nebula
Visible to the naked eye as a hazy patch, the Lagoon Nebula is a glowing cloud of gas and dust actively birthing new stars about 4,000 light-years away.
Lagrangian Point
These five gravitational “parking spots” between two orbiting bodies, like Earth and the Sun, let spacecraft such as the James Webb Space Telescope hold a stable position.
Lambda-CDM Model
This leading model explains the cosmos using dark energy (lambda) and cold dark matter, describing how the universe expanded and formed galaxies since the Big Bang.
Laniakea Supercluster
Spanning roughly 500 million light-years, Laniakea is the enormous galactic “supercluster” home that includes our Milky Way, the Virgo Cluster, and thousands of other galaxies.
Large Magellanic Cloud
Visible from the Southern Hemisphere as a cloudy smudge, this satellite galaxy is one of the Milky Way’s closest neighbors and a hotspot for studying star formation.
Lava Tube
Found on the Moon and Mars, these hollow, cave-like structures form when the surface of a lava flow cools while liquid rock still drains out beneath it.
Leap Second
Because Earth’s spin gradually drifts, timekeepers insert a leap second now and then so atomic clocks stay in sync with the actual length of a day.
Leo
One of the most recognizable constellations, Leo features a backwards-question-mark “sickle” of stars and the bright star Regulus marking the lion’s heart.
Leo Minor
Wedged between Leo and Ursa Major, Leo Minor is a dim, minor constellation with no bright stars, added to fill a gap on star charts.
Lepus
Sitting just beneath Orion’s feet, Lepus is a modest constellation whose stars trace the outline of a hare being chased across the sky.
Libra
The only zodiac sign depicted as an object rather than a creature, Libra’s stars form a faint quadrilateral once considered part of neighboring Scorpius.
Libration
Because the Moon’s orbit and rotation aren’t perfectly matched, it appears to rock slightly back and forth, letting observers see about 59 percent of its surface over time.
Light Curve
Astronomers plot light curves to track flickering stars, eclipsing binaries, or transiting exoplanets, since dips and swings in brightness reveal hidden orbital and physical details.
Light Pollution
Streetlights and city glow wash out faint stars and the Milky Way, making light pollution one of the biggest obstacles to stargazing and observational astronomy today.
Light-Year
Used to measure vast cosmic distances, a light-year describes how far a beam of light travels in 365 days rather than a unit of time itself.
Limb
When observing the Sun, Moon, or planets, the limb is the curved boundary of their disk as seen from Earth, useful for timing eclipses and occultations.
Line of Nodes
This imaginary line marks where an object’s orbit crosses a reference plane, such as Earth’s, and it determines when eclipses or transits can occur.
Local Arm
Also called the Orion Arm, this modest spur of the galaxy’s spiral structure is home to our solar system, tucked between two larger galactic arms.
Local Bubble
Carved out by ancient supernova explosions, this roughly 300-light-year-wide region of sparse interstellar gas envelops the Sun and its nearby stellar neighbors.
Local Group
This collection of roughly 80 galaxies, dominated by the Milky Way and Andromeda, is bound together by gravity within a region about 10 million light-years across.
Local Sidereal Time
Astronomers use this star-based clock to know which part of the sky is overhead, since it tracks Earth’s spin against distant stars instead of solar time.
Local Void
This enormous, galaxy-poor stretch of the cosmos borders our galactic neighborhood, and its emptiness is thought to gently push nearby galaxies outward.
Long-Period Comet
Originating from the distant Oort Cloud, these comets swing into the inner solar system on wildly elongated orbits, often appearing only once in a lifetime.
Look-back Time
Because light takes time to travel, observing a distant galaxy means seeing it as it existed long ago; look-back time measures how far into that past we’re peering.
Low Earth Orbit
Most satellites, the International Space Station, and crewed missions operate here, close enough to Earth for quick access but still officially in space.
Luminosity
This intrinsic brightness measurement tells astronomers how much light and energy a star truly puts out, independent of how far away or dim it appears from Earth.
Luminosity Class
Ranging from supergiants to dwarfs, this labeling system helps astronomers distinguish stars of similar temperature but very different sizes and true brightness.
Luminosity Function
Astronomers use this tool to count and compare stars or galaxies of different brightness within a population, revealing patterns in cosmic structure and evolution.
Luminous Blue Variable
These short-lived giants undergo dramatic brightness outbursts and shed huge amounts of mass, making them some of the most volatile and luminous stars known.
Lunar Eclipse
This occurs when Earth passes directly between the Sun and Moon, often turning the Moon a reddish “blood moon” color as sunlight bends through Earth’s atmosphere.
Lunar Highlands
Older and more rugged than the dark maria, these bright, crater-pocked highlands make up most of the Moon’s surface and record billions of years of impacts.
Lunar Maria
Latin for “seas,” these basaltic plains formed from ancient volcanic lava flows and give the Moon’s near side its familiar dark splotches visible from Earth.
Lunar Meteorite
Blasted off the lunar surface by asteroid impacts, these rare rocks eventually fall to Earth, giving scientists Moon samples without a dedicated sample-return mission.
Lunar Month
Lasting about 29.5 days, this cycle from one new moon to the next is the basis for many traditional calendars around the world.
Lunar Occultation
As the Moon moves across the sky, it occasionally blocks more distant objects from Earth’s view, letting astronomers time the disappearance precisely.
Lunar Phase
From new moon to full moon and back, these familiar shapes result from changing angles between the Sun, Earth, and Moon over about a month.
Lunar Regolith
Formed by billions of years of meteorite impacts pulverizing rock, this fine, abrasive dust blankets the lunar surface and clung stubbornly to Apollo astronauts’ suits.
Lunar Terminator
This boundary between light and shadow creates dramatic long shadows on the lunar surface, making it a favorite target for telescope observers.
Lyman-Alpha Line
This bright ultraviolet emission line helps astronomers detect hydrogen gas across the universe and measure the distances and properties of very remote galaxies.
Lyman-Break Galaxy
Hydrogen gas absorbs certain ultraviolet light from these far-off galaxies, creating a detectable “break” in their spectrum that helps astronomers find galaxies from the early universe.
Lyra
Though compact, Lyra hosts Vega, one of the brightest stars in the night sky, along with the famous Ring Nebula.
Lyrid Meteor Shower
Occurring every April, this shower produces bright, fast meteors and is one of the oldest recorded meteor showers, observed for over 2,700 years.