Space and Astronomy Vocabulary in English

How much sunlight a planet or moon reflects back into space.

• The ice on Earth reflects a lot of light, so our planet has a high albedo.
• Scientists use the albedo of the Moon to predict how bright it will look.
• A dark surface has a low albedo and becomes hot very quickly.

The nearest large galaxy to our own Milky Way.

• On a very dark night, you can see Andromeda without a telescope.
• Scientists say Andromeda and the Milky Way will meet in a few billion years.
• The Andromeda galaxy holds more than a trillion stars.

A rare kind of matter that destroys normal matter when they touch.

• When matter meets antimatter, both change into a flash of energy.
• Scientists can make tiny bits of antimatter in huge machines on Earth.
• Some faraway explosions in space may come from meeting antimatter.

The opening of a telescope that lets light in; a bigger aperture shows fainter objects.

• A telescope with a large aperture can collect more light from faint stars.
• The aperture of the biggest telescopes is ten meters wide.
• Amateur astronomers always check the aperture before buying a telescope.

The point in the orbit of a planet where it is farthest from the Sun.

• Earth reaches aphelion in early July, when it is farthest from the Sun.
• At aphelion, the Sun looks a tiny bit smaller in our sky.
• The comet slowly drifts toward aphelion, far beyond Neptune.

The point in an orbit that is farthest from Earth.

• The satellite takes pictures when it is near apogee, high above Earth.
• At apogee, the spacecraft moves more slowly than at any other time.
• The Moon at apogee is about 405,000 kilometers from Earth.

A machine made by people that travels around Earth or another planet.

• The first artificial satellite, Sputnik, launched in 1957.
• Weather forecasts use pictures from artificial satellites.
• Thousands of artificial satellites circle Earth right now.

A small rocky object that travels around the Sun.

• Most asteroids live in the big belt between Mars and Jupiter.
• A huge asteroid hit Earth millions of years ago and changed life forever.
• Space agencies send robots to study the surface of an asteroid.

A person who travels into space.

• The astronaut floated through the space station and looked down at Earth.
• Astronauts train for years before their first trip into space.
• Neil Armstrong was the first astronaut to walk on the Moon.

A scientist who studies stars, planets, and everything else in space.

• The astronomer spent the whole night watching the sky with a big telescope.
• Astronomers use computers to study the light from distant stars.
• As a child, the astronomer loved counting stars from her window.

The science that studies objects in space, such as stars and planets.

• Astronomy helps us understand where Earth fits in the universe.
• She joined the astronomy club to learn more about the planets.
• Ancient people used astronomy to know when to plant their crops.

The branch of science that explains how stars and galaxies work.

• Astrophysics explains why the Sun shines and how black holes form.
• He studied astrophysics at university to learn about dying stars.
• New telescopes give astrophysics students amazing data every day.

The layer of gases that surrounds a planet or star.

• The atmosphere protects us from harmful rays from space.
• The atmosphere of Mars is very thin and full of dust.
• A spacecraft needs a heat shield to enter the atmosphere safely.

Moving sheets of colorful light that appear in the sky near the poles.

• The green aurora danced above the frozen lake in Norway.
• An aurora appears when tiny particles from the Sun hit the air.
• Tourists travel far north in winter to watch the aurora.

The shared center point that two orbiting objects swing around.

• The barycenter of Earth and the Moon lies inside Earth, not between them.
• Pluto and its moon Charon swing around a barycenter in open space.
• Astronomers find distant planets by watching how a star wobbles around its barycenter.

A huge red star in the constellation Orion that may explode one day.

• Betelgeuse glows orange-red on the shoulder of Orion.
• If Betelgeuse exploded, it would shine almost as bright as the Moon for weeks.
• Betelgeuse is so big that it would reach past the orbit of Mars.

The giant explosion that started the universe about 13.8 billion years ago.

• Scientists study very old light to learn about the big bang.
• According to the big bang theory, space itself began to stretch and grow.
• The universe has been cooling slowly ever since the big bang.

A pair of stars that travel around each other.

• Through a telescope, a far binary star can look like one single point of light.
• Many stars in our galaxy are really binary stars.
• A planet around a binary star would enjoy a double sunset.

A place in space where gravity is so strong that even light cannot escape.

• Light that gets too close to a black hole disappears forever.
• Scientists photographed a black hole for the first time in 2019.
• A black hole forms when a giant star dies and collapses.

The change that makes light from an object moving toward us look bluer.

• Astronomers saw a clear blueshift in the light of that approaching star.
• Blueshift tells scientists that a galaxy is moving closer to Earth.
• The opposite of blueshift is called redshift.

A rocket engine that gives a spacecraft the power to leave Earth.

• The booster fell into the sea after giving the rocket its first push.
• Two side boosters helped the heavy rocket rise from the launch pad.
• The space company lands its boosters and uses them again.

How much light an object in space gives off or reflects.

• The brightness of a star can slowly change as it gets older.
• Astronomers measured the brightness of the supernova from far away.
• City lights reduce the brightness of the stars we can see.

A failed star that is too small to shine like a normal star.

• A brown dwarf glows faintly because it cannot fully start nuclear fusion.
• Astronomers found a brown dwarf floating alone between the stars.
• A brown dwarf is bigger than a planet but smaller than a star.

Connected with the sky or with objects in space.

• The Moon is the brightest celestial object in the night sky.
• Ancient sailors used celestial maps to find their way across the sea.
• A bright comet is a beautiful celestial visitor.

The largest object in the asteroid belt, now called a dwarf planet.

• Ceres is the closest dwarf planet to the Sun.
• A spacecraft called Dawn studied the craters of Ceres.
• Ceres may hide salty water under its rocky surface.

The lower layer of the atmosphere of the Sun, just above the bright surface.

• During an eclipse, the chromosphere glows red around the edge of the Moon.
• The temperature inside the chromosphere reaches thousands of degrees.
• Small jets of hot gas rise from the chromosphere.

A group of stars that were born together and travel together.

• The cluster held hundreds of young blue stars.
• The Pleiades is a famous star cluster you can see without a telescope.
• The stars in a cluster move through space side by side.

The cloud of gas and dust that forms around the core of a comet.

• Sunlight makes the coma of a comet glow softly.
• The coma of a big comet can grow wider than a planet.
• Through a telescope, the comet looked like a fuzzy ball of light.

An icy object that grows a bright tail when it comes near the Sun.

• Halley's Comet returns to our sky about every 76 years.
• The comet stretched across the dawn sky like a silver sword.
• Comets carry ice and dust from the cold edge of the solar system.

An event when two objects in space appear close together in the sky.

• Tonight, Jupiter and Venus will meet in a beautiful conjunction.
• The conjunction of the Moon and Mars looked amazing at sunset.
• Photographers traveled far to capture the rare conjunction of the planets.

A pattern of stars that people imagine as a shape or picture.

• Orion is the easiest constellation to find in the winter sky.
• There are 88 official constellations in the whole sky.
• Long ago, sailors used the constellation of the Great Bear to steer north.

The outer layer of the atmosphere of the Sun, seen during a total eclipse.

• During a total eclipse, the corona shines like a silver crown.
• The corona is strangely hotter than the surface of the Sun.
• Scientists use special telescopes to study the corona between eclipses.

Tiny fast particles from space that fly through everything.

• Cosmic rays hit the atmosphere of Earth from every direction.
• Detectors on high mountains count cosmic rays day and night.
• Astronauts wear extra shielding to stay safe from cosmic rays.

An astronaut from Russia or the former Soviet Union.

• Yuri Gagarin was the first cosmonaut to orbit Earth.
• The cosmonaut trained with the international crew for eighteen months.
• A cosmonaut and an astronaut worked side by side on the space station.

The whole universe seen as one enormous system.

• The cosmos is filled with billions of galaxies.
• Ancient thinkers wondered how the cosmos began.
• New telescopes help us see deeper into the cosmos.

A round hole on a planet or moon made by a rock falling from space.

• The Moon is covered with craters of every size.
• Astronauts studied the steep wall of a huge crater on the Moon.
• Meteor Crater in Arizona was made by a falling space rock.

The curved shape of the Moon when only a thin slice is lit.

• A thin crescent hung above the trees after sunset.
• The crescent of the new moon glowed orange in the evening sky.
• Some calendars begin each month with the first crescent.

A mysterious force that makes the universe expand faster and faster.

• Scientists think dark energy makes up most of the universe.
• Nobody knows what dark energy really is.
• Dark energy pushes the galaxies away from each other.

Invisible material in space that we can detect only by its gravity.

• Dark matter holds the galaxies together like invisible glue.
• Telescopes cannot see dark matter, but scientists can measure its pull.
• There is about five times more dark matter than normal matter.

The position of a star measured north or south of the equator of the sky.

• Every star map shows the declination of each object.
• A star with a declination of zero rises almost exactly in the east.
• Astronomers use declination like latitude on a map of the sky.

The far parts of space, far away from Earth and the Sun.

• Powerful telescopes can catch faint light from deep space.
• The probe traveled for years before it reached deep space.
• Radio messages from deep space take hours to reach us.

The change in waves when the thing making them moves toward or away from you.

• The Doppler shift of starlight shows whether a star moves toward us or away.
• A siren sounds lower after it passes you because of the Doppler shift.
• Police radar uses the Doppler shift to check the speed of cars.

Tiny particles of rock and ice that float between the stars.

• A cloud of dust can block the light of the stars behind it.
• Comets leave a trail of dust as they fly near the Sun.
• Space dust falls onto Earth quietly every day.

A round object that orbits the Sun but is too small to clear its own path.

• Pluto became a dwarf planet in 2006.
• Ceres is a dwarf planet that lives inside the asteroid belt.
• Scientists have found several dwarf planets beyond Neptune.

The planet we live on, the third planet from the Sun.

• From space, Earth looks like a small blue marble.
• Earth is the only planet known to have life.
• The Moon travels around Earth once every month.

An event when one object in space hides another from view.

• During a solar eclipse, the Moon slowly covers the Sun.
• Thousands of people traveled to see the total eclipse.
• A lunar eclipse happens when the shadow of Earth falls on the Moon.

The invisible path that the Sun appears to follow across the sky during the year.

• The planets always stay close to the ecliptic.
• The Moon crossed the ecliptic and hid the bright star.
• Ancient astronomers drew the ecliptic on their star charts.

All the kinds of light together, from radio waves to gamma rays.

• Visible light is only a small part of the electromagnetic spectrum.
• Telescopes study the electromagnetic spectrum to see hidden things in space.
• X-rays and radio waves both belong to the electromagnetic spectrum.

Shaped like a stretched circle, an oval.

• Planets move in elliptical orbits, not in perfect circles.
• The comet follows a long elliptical path around the Sun.
• Some galaxies are round, and others are elliptical.

The day in spring and autumn when day and night are almost equal.

• The spring equinox arrives around March 20 every year.
• At the equinox, the Sun rises almost exactly in the east.
• Old monuments were built to line up with the equinox sunrise.

The speed a spacecraft needs to break free from the gravity of a planet.

• A rocket must reach escape velocity to leave Earth.
• Escape velocity from Earth is about 11 kilometers every second.
• The probe had enough speed to escape the whole solar system.

The planet Venus when it shines brightly in the western sky after sunset.

• Look for the evening star just after the Sun goes down.
• Ancient people thought the evening star and the morning star were two different objects.
• Venus plays the evening star for several months each year.

A planet that travels around a star outside our solar system.

• Scientists have discovered more than five thousand exoplanets.
• The new space telescope will study the air of each exoplanet.
• One famous exoplanet has two suns in its sky.

Coming from somewhere beyond planet Earth.

• Scientists search for extraterrestrial life with giant radio dishes.
• The movie is about extraterrestrial visitors who land in a small town.
• Meteorites sometimes carry extraterrestrial minerals.

A huge arc of glowing gas that hangs above the surface of the Sun.

• A solar filament stretched across the face of the Sun for days.
• When a filament collapses, it can start a big eruption.
• Through the special telescope, the filament looked like a red bridge of fire.

An unusually bright meteor that lights up the whole sky.

• The fireball turned night into day for one second.
• People reported a green fireball streaking over the mountains.
• A fireball is simply a larger rock burning in our atmosphere.

The moon phase, one week after the new moon, when half of the lit side faces Earth.

• The first quarter moon always sets around midnight.
• At first quarter, you can see the Moon even in the afternoon.
• Craters look deepest along the edge at first quarter.

A sudden, powerful burst of energy from the Sun.

• A strong solar flare can disturb radio signals on Earth.
• The flare shot out from a group of dark sunspots.
• Scientists watch the Sun closely to warn us about big flares.

A trip when a spacecraft passes close to a planet without landing.

• The probe took stunning pictures during its flyby of Jupiter.
• The flyby gave the spacecraft extra speed from the gravity of the planet.
• New Horizons made a famous flyby of Pluto in 2015.

The moon phase when the whole bright side faces Earth.

• The full moon rose just as the Sun went down.
• Wolves howled at the bright full moon in the old stories.
• Farmers once used the names of each full moon to follow the seasons.

A huge family of stars, gas, and dust held together by gravity.

• Our galaxy, the Milky Way, holds over one hundred billion stars.
• The photo shows a spiral galaxy with glowing arms.
• Galaxies drift away from each other as the universe grows.

The most powerful kind of light, with very short waves.

• Gamma rays come from exploding stars and black holes.
• Special satellites detect gamma rays from deep space.
• Too many gamma rays are dangerous for living things.

The largest moon of Jupiter and the biggest moon in the solar system.

• Ganymede is even bigger than the planet Mercury.
• Ganymede may hide a salty ocean under its icy shell.
• The spacecraft Juno flew past Ganymede and sent home new pictures.

A huge planet made mostly of gas, like Jupiter and Saturn.

• Jupiter is the largest gas giant in our solar system.
• Gas giants have no solid ground to stand on.
• A single storm on that gas giant has raged for centuries.

Describing the old idea that Earth is the center of everything.

• People believed the geocentric model for more than a thousand years.
• Copernicus showed that the geocentric idea was wrong.
• In the geocentric view, the Sun appears to circle Earth.

Describing a satellite that stays above the same spot on Earth.

• Weather satellites use geostationary orbits to watch one region all day.
• A geostationary satellite must fly about 36,000 kilometers high.
• Television signals often come from geostationary satellites.

Describing the Moon when it is more than half lit but not yet full.

• The gibbous moon shone brightly over the quiet fields.
• Between first quarter and full moon, the Moon looks gibbous.
• Through binoculars, the gibbous Moon shows hundreds of craters.

A giant round ball of very old stars packed close together.

• The globular cluster held nearly a million tightly packed stars.
• Through a small telescope, a globular cluster looks like glowing sugar.
• Astronomers have found about 150 globular clusters around our galaxy.

The force that pulls objects toward each other.

• Gravity keeps the Moon traveling around Earth.
• On the Moon, gravity is much weaker, so astronauts can jump high.
• Without gravity, everything on Earth would float away.

A ring of light around an object, such as the Moon or a galaxy.

• A bright halo circled the Moon on the frosty night.
• Our galaxy sits inside a huge halo of dark matter.
• Ice crystals high in the air can make a halo around the Sun.

Describing the idea that the Sun is the center of the solar system.

• Copernicus taught the heliocentric model long ago.
• In the heliocentric system, Earth circles the Sun once a year.
• It took centuries for people to accept the heliocentric idea.

The far edge of the influence of the Sun, where interstellar space begins.

• Voyager 1 crossed the heliopause and entered deep space.
• The heliopause lies more than a hundred times farther from the Sun than Earth.
• The solar wind stops at the heliopause.

The giant bubble of solar wind that surrounds the Sun and all the planets.

• The heliosphere shields us from some cosmic rays.
• Every planet in the solar system lives inside the heliosphere.
• The heliosphere travels with the Sun through the galaxy.

One half of a planet or of the sky.

• The Northern Hemisphere has summer when the Southern Hemisphere has winter.
• From Australia, people see different constellations in their hemisphere.
• A huge dust storm covered the southern hemisphere of Mars.

A famous telescope that orbits Earth and takes pictures of deep space.

• The Hubble Space Telescope captured the birth of new stars.
• It has sent home more than a million observations.
• Astronauts flew to the Hubble Space Telescope to repair it.

The lightest and most common gas in the universe.

• Stars like the Sun burn hydrogen to make light and heat.
• Clouds of hydrogen slowly gather to form new stars.
• Most of the gas in the universe is hydrogen.

A cold planet made mostly of icy materials, like Uranus and Neptune.

• Uranus is an ice giant tipped completely on its side.
• Ice giants look blue because of methane high in their air.
• Only one spacecraft has ever visited an ice giant.

The tilt of an orbit compared to a flat reference plane.

• The comet has a steep inclination, crossing the planets from below.
• Satellites choose a low inclination to stay near the equator.
• Astronomers measured the inclination of the new orbit.

Describing light with waves too long for our eyes to see, which we feel as heat.

• Infrared telescopes find baby stars hidden inside dust clouds.
• Some snakes can sense infrared heat from their prey.
• Remote controls use infrared signals to change the channel.

The four small rocky planets closest to the Sun: Mercury, Venus, Earth, and Mars.

• The inner planets are much smaller than the gas giants.
• Mercury, the fastest inner planet, races around the Sun in 88 days.
• All the inner planets have solid rocky surfaces.

Between the planets of a solar system.

• Interplanetary space between Mars and Jupiter is full of asteroids.
• The probe began its long interplanetary journey to Saturn.
• Interplanetary radio messages take many minutes to arrive.

Between the stars.

• Voyager 1 became the first interstellar spacecraft in 2012.
• Interstellar space is not empty; thin gas floats between the stars.
• An interstellar visitor named Oumuamua passed through our solar system.

A high layer of the atmosphere of Earth that is full of charged particles.

• The ionosphere bounces radio signals to faraway places.
• Beautiful auroras glow inside the ionosphere near the poles.
• The ionosphere protects us from some space radiation.

Connected with Jupiter, or describing planets that are like Jupiter.

• Jupiter is named after Jove, so its moons are called Jovian moons.
• Gas giants are sometimes called Jovian planets.
• The Jovian storm called the Great Red Spot is wider than Earth.

A NASA spacecraft that studies Jupiter from orbit.

• Juno arrived at Jupiter in 2016 after a five-year trip.
• Juno flies low over the poles of Jupiter to study its storms.
• The Juno mission sends back amazing pictures of the clouds of Jupiter.

The largest planet in the solar system, a huge gas giant.

• Jupiter has more than 90 known moons.
• The Great Red Spot on Jupiter is a storm bigger than Earth.
• Jupiter spins so fast that its day lasts only ten hours.

A NASA telescope that searched for planets around other stars.

• The Kepler Space Telescope found thousands of exoplanets.
• Kepler watched one patch of sky for years to catch tiny dips in starlight.
• Thanks to Kepler, we know that most stars have planets.

A huge explosion made when two super-dense dead stars crash into each other.

• A kilonova forges gold and silver in its burning fire.
• Astronomers spotted a kilonova for the first time in 2017.
• The gold in a ring may have come from a kilonova.

A wide ring of icy bodies beyond the orbit of Neptune.

• Pluto and many short-period comets come from the Kuiper Belt.
• The Kuiper Belt begins about 4.5 billion kilometers from the Sun.
• New Horizons became the first spacecraft to explore the Kuiper Belt.

A spacecraft designed to land softly on a planet or moon.

• The lander touched down gently on the red dust of Mars.
• A lander must slow down carefully before reaching the ground.
• A robotic lander brought Moon rocks back to Earth in 2020.

The moment when a rocket leaves the ground.

• We watched the launch from a beach ten kilometers away.
• The launch was delayed for two days because of strong winds.
• Countdown, engine fire, liftoff: a rocket launch is exciting to watch.

A curved piece of glass that gathers and focuses light in a telescope.

• The lens of the telescope gathers starlight into a sharp point.
• Galileo used a small lens to discover the moons of Jupiter.
• A bigger lens collects more light from faint objects.

Too much artificial light that hides the stars at night.

• In big cities, light pollution lets you count only a few stars.
• Dark-sky parks protect the night from light pollution.
• You can see the Milky Way only far away from light pollution.

The distance light travels in one year, about 9.5 trillion kilometers.

• The nearest star after the Sun is a little over four light-years away.
• Light from that galaxy traveled millions of light-years to reach us.
• A light-year measures distance, not time.

Connected with the Moon.

• A lunar rover left long tracks in the gray dust of the Moon.
• Many calendars follow the lunar cycle of about 29 days.
• The astronauts collected lunar rocks during their moonwalk.

One complete cycle of the phases of the Moon, about 29.5 days.

• A lunation begins with the new moon.
• Ancient sky watchers counted time by each lunation.
• The full moon arrives about two weeks into every lunation.

The magnetic bubble around a planet that shields it from the solar wind.

• The magnetosphere of Earth pushes the solar wind around our planet.
• When solar storms hit the magnetosphere, auroras light up the poles.
• The magnetosphere of Jupiter is the biggest of any planet.

The measure of how bright a star or planet looks from Earth.

• Bright stars have small magnitude numbers, and faint stars have big ones.
• The student measured the magnitude of every star in the Little Dipper.
• A difference of one magnitude means a big change in brightness.

The long, stable stage in the life of a star when it burns hydrogen.

• Our Sun will stay on the main sequence for about ten billion years.
• Most stars in the sky are main sequence stars.
• When a star leaves the main sequence, it begins to swell and change.

A dark, flat plain of old lava on the Moon; the word means sea.

• The Sea of Tranquility is a famous mare on the Moon.
• Early astronomers thought each mare was filled with water.
• You can spot a dark mare with just your own eyes.

The fourth planet from the Sun, known as the Red Planet.

• Mars looks red because its dust is full of rusty iron.
• Robots drive across Mars every day and send home pictures.
• People hope to visit Mars in the coming decades.

The smallest planet and the closest one to the Sun.

• Mercury races around the Sun faster than any other planet.
• On Mercury, daytime is hot enough to melt metal.
• A spacecraft called Messenger mapped the craters of Mercury.

A streak of light made when a small space rock burns in our air.

• A bright meteor crossed the sky during the camping trip.
• The best time to see a meteor is after midnight.
• Most meteors burn up completely before they reach the ground.

Many meteors that seem to fly out from one point in the sky.

• The Perseid meteor shower fills August nights with shooting stars.
• We lay on blankets and counted meteors during the meteor shower.
• A meteor shower happens when Earth passes through the dust trail of a comet.

A space rock that survives the trip through the air and lands on the ground.

• The museum keeps a huge meteorite that fell a thousand years ago.
• A meteorite crashed through the roof of an empty garage.
• Scientists cut meteorites open to study the metal inside.

A small piece of rock floating in space before it meets an atmosphere.

• A meteoroid becomes a meteor only when it burns in the air.
• Many meteoroids are no bigger than a grain of rice.
• Comets drop meteoroids all along their path around the Sun.

Our home galaxy, which looks like a band of light from inside.

• On dark nights, the Milky Way stretches like a river of stars.
• The Milky Way holds hundreds of billions of stars.
• Ancient Greeks saw the Milky Way as spilled milk across the sky.

Another name for a small object, like an asteroid, that orbits the Sun.

• Astronomers gave the minor planet a number and a name.
• Ceres was the first minor planet ever discovered.
• Astronomers add thousands of minor planets to the official catalog every year.

A curved, shiny surface that gathers light in a reflecting telescope.

• The mirror of the giant telescope is eight meters wide.
• A telescope mirror must be polished perfectly to make sharp images.
• Light bounces off the mirror and into the eyepiece.

A natural object that travels around a planet; Earth has exactly one.

• The Moon causes the tides in our oceans.
• Twelve astronauts have walked on the Moon so far.
• The moon Europa may hide an ocean under its ice.

The planet Venus when it shines in the eastern sky before sunrise.

• The morning star glowed above the rooftops just before dawn.
• Sailors once used the morning star to find the east.
• The same planet is the morning star at one time of year and the evening star at another.

The point in the sky directly below your feet.

• The zenith is above your head, and the nadir is under your feet.
• Astronauts look straight down toward the nadir to photograph the ground.
• The satellite pointed its camera at the nadir to map the streets.

A giant cloud of gas and dust in space where stars are born.

• The Orion Nebula is easy to find with small telescopes.
• Inside a nebula, baby stars begin to glow.
• The colors in a nebula come from different glowing gases.

A tiny, almost massless particle that flies through almost everything.

• Trillions of neutrinos from the Sun pass through your body every second.
• Scientists built detectors deep underground to catch neutrinos.
• A neutrino can fly through a whole planet without touching anything.

The super-dense core left behind after a giant star explodes.

• A teaspoon of neutron star would weigh about a billion tons.
• Some neutron stars spin hundreds of times every second.
• A neutron star packs a whole sun into a ball the size of a city.

The moon phase when the Moon sits between Earth and the Sun and cannot be seen.

• The sky is darkest at new moon, which is perfect for stargazing.
• A solar eclipse can only happen at new moon.
• The lunar month begins at each new moon.

A sudden bright flare-up when a dead star steals gas from a neighbor.

• The nova shone like a new star for a few weeks.
• Ancient astronomers recorded a nova almost a thousand years ago.
• After the nova faded, the star returned to its old dim self.

The joining of light atoms that releases huge energy and powers the stars.

• The Sun makes light through nuclear fusion in its core.
• Nuclear fusion turns hydrogen into helium inside every star.
• Scientists on Earth are trying to build clean power from nuclear fusion.

A building with telescopes that is used for studying the sky.

• The mountain observatory has some of the clearest skies in the world.
• Students visited the observatory to look at the rings of Saturn.
• Modern observatories sit on high mountains, far from city lights.

The hiding of a star when a planet or moon passes in front of it.

• The occultation of the bright star by the Moon lasted an hour.
• During an occultation, the star disappears behind the edge of the planet.
• Astronomers time an occultation to learn the size of distant objects.

A giant sphere of icy bodies at the very edge of the solar system.

• Long-period comets are thought to come from the Oort Cloud.
• The Oort Cloud may stretch a light-year from the Sun.
• No spacecraft has ever reached the Oort Cloud.

The time when a planet is opposite the Sun, so it is close, bright, and visible all night.

• Mars shines all night long around its opposition.
• The next opposition of Jupiter is the best time to see its cloudy bands.
• During opposition, a planet rises at sunset and sets at sunrise.

The curved path that one space object follows around another.

• The space station completes one orbit of Earth every 90 minutes.
• The satellite slipped into a steady orbit around Mars.
• Some comets follow orbits that take thousands of years.

A bright winter constellation shaped like a hunter with a belt of three stars.

• Orion is easy to spot because of the three stars in a straight line.
• On winter evenings, Orion climbs high above the rooftops.
• Many cultures told different stories about the stars of Orion.

The four giant planets far from the Sun: Jupiter, Saturn, Uranus, and Neptune.

• The outer planets are all much bigger than Earth.
• Unlike the inner planets, the outer planets have rings and many moons.
• Spacecraft have visited every one of the outer planets.

The small shift in the position of a nearby star as Earth moves around the Sun.

• Astronomers use parallax to measure the distance to close stars.
• Hold a thumb at arm's length and blink each eye to see parallax for yourself.
• The parallax of very distant stars is far too tiny to notice.

A unit for measuring huge distances in space, about 3.26 light-years.

• The nearest star sits a little more than one parsec away.
• Astronomers describe the distances to galaxies in millions of parsecs.
• One parsec equals about 3.26 light-years.

The lighter outer part of a shadow, where only some light is blocked.

• In the penumbra of the eclipse, the daylight turns strangely pale.
• A penumbral lunar eclipse is hard to notice with your own eyes.
• A sunspot has a dark center and a lighter penumbra around it.

The point in an orbit that is closest to Earth.

• The Moon looks slightly bigger at perigee, its closest point.
• A supermoon happens when a full moon meets perigee.
• The satellite moves at its fastest speed near perigee.

The point in an orbit that is closest to the Sun.

• Earth is slightly closer to the Sun at perihelion in January.
• The comet blazes brightest just after perihelion.
• At perihelion, the ice of the comet begins to boil away.

One of the changing shapes of the lit part of the Moon.

• The phases of the Moon repeat every month, from new to full.
• We drew each phase of the Moon in our science notebooks.
• Venus also shows phases when seen through a telescope.

The smallest possible packet of light.

• Every ray of sunlight is really a stream of photons.
• A photon from a far galaxy may travel billions of years to reach your eye.
• Solar panels turn photons from the Sun into electricity.

The bright, visible surface of the Sun.

• The photosphere glows at about 5,500 degrees Celsius.
• Dark sunspots appear on the photosphere of the Sun.
• During a total eclipse, the Moon briefly hides the photosphere.

A large round object that orbits a star and clears its own path.

• Earth is the third planet from the Sun.
• Astronomers have found planets around thousands of other stars.
• A day on each planet in our solar system is a different length.

A theater with a domed ceiling that shows the stars and planets.

• The class trip to the planetarium felt like a journey through space.
• At the planetarium, we watched the whole sky spin above our heads.
• The planetarium projects thousands of stars onto its dome.

Super-hot gas where electrons are torn from atoms, the fourth state of matter.

• Stars are giant balls of glowing plasma.
• Auroras are made of plasma that arrives with the solar wind.
• Neon signs glow because of plasma inside the tubes.

The most famous dwarf planet, once counted as the ninth planet.

• Pluto is smaller than the Moon of Earth.
• New Horizons showed that Pluto has a huge heart-shaped glacier.
• Pluto takes 248 years to circle the Sun once.

The North Star, which sits almost exactly above the North Pole of Earth.

• Travelers in the north used Polaris to find true north.
• Polaris sits at the end of the handle of the Little Dipper.
• The whole night sky seems to spin around Polaris.

An unmanned spacecraft that explores space and sends back data.

• The probe flew past Saturn and studied its icy rings.
• A probe does not carry people, only scientific instruments.
• The old probe ended its mission by diving into the clouds of Saturn.

A huge loop of glowing gas that rises from the edge of the Sun.

• A red prominence arced above the edge of the Sun during the eclipse.
• A solar prominence can stretch for hundreds of thousands of kilometers.
• Photographers love to catch a prominence just after totality.

A spinning neutron star that sends out beams of radio waves like a lighthouse.

• This pulsar flashes thirty times every second, steady as a clock.
• Jocelyn Bell discovered the first pulsar in 1967.
• A pulsar is like a cosmic lighthouse spinning in the dark.

A moon phase when exactly half of the face of the Moon is lit.

• Tonight the quarter moon will hang high at sunset.
• The quarter moon is perfect for viewing craters along the shadow line.
• There are two quarter moons in every lunar month.

The extremely bright core of a distant galaxy, powered by a giant black hole.

• Quasars are the brightest objects seen from very far away.
• Light from that quasar left home more than ten billion years ago.
• A quasar can outshine a thousand galaxies together.

Energy that travels as waves or as fast particles through space.

• Space is full of radiation that can harm astronauts.
• The spacecraft carries shields to protect its crew from radiation.
• Telescopes collect radiation from stars to make their pictures.

A large dish that catches radio waves from space.

• The radio telescope in the valley measures 500 meters across.
• Radio telescopes can see through dust clouds that hide the stars.
• The team pointed the radio telescope at a distant pulsar.

A long, invisible wave that can carry information or signals.

• Radio waves from space were first discovered by accident in 1932.
• The spacecraft sends its data home as radio waves.
• Radio waves travel at the speed of light.

The smallest and coolest kind of true star, which burns very slowly.

• Red dwarfs can keep shining for trillions of years.
• The nearest star to the Sun is a red dwarf called Proxima Centauri.
• Planets around a red dwarf would be lit with a dim orange glow.

A huge, old star that has swollen as its fuel runs low.

• Our Sun will become a red giant in about five billion years.
• The red giant glowed deep orange in the autumn sky.
• A red giant is bright even though its surface is cool.

The stretching of light from objects that are moving away from us.

• The redshift of far galaxies shows that the universe is growing.
• A bigger redshift means the galaxy is racing away faster.
• Edwin Hubble found redshift in the light of faraway galaxies.

Moving or spinning backward compared to the normal direction.

• Venus spins in retrograde, so the Sun there rises in the west.
• At times, Mars appears to move in retrograde across our sky.
• That moon follows a retrograde orbit around its planet.

A wide, flat circle of ice and rock that circles a planet.

• The rings of Saturn are made of countless pieces of ice.
• Jupiter, Uranus, and Neptune also have faint rings.
• The Voyager probe showed us the rings up close.

A robot vehicle that drives across the surface of another world.

• The rover climbed a hill on Mars to study the rocks.
• The rover of China sent pictures from the far side of the Moon.
• Each rover moves slowly, testing the ground ahead.

An object that travels around a planet or star, natural or man-made.

• The Moon is the only natural satellite of Earth.
• Communication satellites carry our phone calls around the world.
• The satellite beams weather pictures down every hour.

The sixth planet from the Sun, famous for its beautiful rings.

• Saturn is so light that it could float in a giant bathtub.
• The rings of Saturn stretch far into space but are very thin.
• Titan, the largest moon of Saturn, has lakes of liquid methane.

The bright streak of a small rock burning in the air; a meteor.

• Make a wish when you see a shooting star.
• We saw three shooting stars during the Perseid shower.
• A shooting star is not a star at all.

A spacecraft that can fly to space, land like a plane, and fly again.

• The space shuttle launched 135 times between 1981 and 2011.
• The shuttle carried big parts of the space station into orbit.
• Astronauts rode the shuttle to repair the Hubble telescope.

The event when the Moon moves in front of the Sun and blocks its light.

• During the solar eclipse, day turned into deep twilight.
• People wore special glasses to watch the solar eclipse safely.
• The next total solar eclipse will cross the continent in August.

A flat device that turns sunlight into electricity.

• The solar panels of the space station stretch as wide as a football field.
• The solar panels of the rover collect energy every Martian morning.
• Dust on a solar panel can lower its power.

The Sun and everything that travels around it: planets, moons, and more.

• Our solar system has eight planets and hundreds of moons.
• Models of the solar system are never true to scale.
• The solar system was born from a spinning cloud of gas and dust.

A steady flow of tiny particles that blows out from the Sun in all directions.

• The solar wind pushes the tail of a comet away from the Sun.
• Strong solar wind can make auroras dance over the poles.
• The solar wind carries the breath of the Sun across the whole system.

The longest or shortest day of the year, in June and December.

• The summer solstice brings the most daylight of the whole year.
• Ancient people built monuments that line up with the winter solstice sunrise.
• After the December solstice, the days slowly grow longer again.

A large spacecraft where astronauts live and work in orbit.

• The space station circles Earth sixteen times every day.
• Crews from many countries share the work on the space station.
• The space station flies about 400 kilometers above our heads.

Any vehicle that travels in space.

• The spacecraft traveled for nine years to reach Pluto.
• Building a spacecraft that can survive deep space is very hard.
• Every spacecraft must carry its own power supply and radio.

A special suit that keeps an astronaut alive outside a spacecraft.

• A spacesuit provides air, water, and protection from heat and cold.
• The spacesuit weighed more than 100 kilograms on Earth.
• Without a spacesuit, an astronaut could not survive one minute outside.

A trip outside a spacecraft by an astronaut in a spacesuit.

• The spacewalk lasted six hours while the crew fixed the antenna.
• During a spacewalk, Earth turned slowly and silently below.
• Tethers keep astronauts safe during every spacewalk.

A tool that splits light into its colors to reveal what stars are made of.

• With a spectroscope, scientists found helium in the Sun before they found it on Earth.
• The spectroscope shows dark lines where gases absorb the light.
• Every element leaves its own fingerprint in a spectroscope.

A galaxy with long, curved arms of stars spinning around a bright center.

• Our Milky Way is a spiral galaxy with long curved arms.
• The photo shows a spiral galaxy seen face-on like a glowing pinwheel.
• Many spiral galaxies have a bar of stars through the middle.

A giant ball of hot glowing gas that makes its own light.

• The Sun is the closest star to Earth.
• Stars come in many colors, from red to blue-white.
• At night, thousands of stars shine over the desert.

The star at the center of our solar system.

• The Sun holds 99.8 percent of all the mass in the solar system.
• Never look straight at the Sun without safe filters.
• Light from the Sun reaches Earth in about eight minutes.

A cooler, darker patch on the surface of the Sun.

• Sunspots appear and disappear in cycles of about 11 years.
• A group of sunspots can grow larger than Earth.
• Galileo was among the first to draw sunspots.

The gigantic explosion of a dying star.

• A supernova can briefly outshine its whole galaxy.
• The supernova of the year 1054 left behind the Crab Nebula.
• Supernova explosions scatter the elements that build new planets.

A tool that collects light to make far objects look closer and brighter.

• Galileo pointed his little telescope at the sky and changed history.
• A good telescope reveals the rings of Saturn from your backyard.
• The mountain observatory uses a telescope with a mirror ten meters wide.

The rocky planets like Earth: Mercury, Venus, Earth, and Mars.

• Terrestrial planets have solid surfaces that you could walk on.
• Unlike the gas giants, the terrestrial planets are small and dense.
• All four terrestrial planets sit close to the Sun.

The moon phase, one week before the new moon, when half of the lit side faces Earth.

• The third quarter moon rises near midnight.
• At third quarter, a half-lit Moon hangs high in the morning sky.
• After third quarter, the Moon shrinks to a thin crescent.

The slow rise and fall of the sea, caused mostly by the Moon.

• The full moon and the new moon bring the strongest tides.
• Tide pools appear on the beach at low tide.
• Sailors check the tide before entering the shallow harbor.

The largest moon of Saturn, wrapped in a thick orange atmosphere.

• Titan is the only moon with rivers and lakes of liquid methane.
• The Huygens probe landed on Titan in 2005.
• Under the haze of Titan, scientists suspect a hidden ocean of water.

The curved path of a moving object, such as a rocket or a comet.

• Engineers calculated the trajectory of the spacecraft with great care.
• The trajectory of the comet will bring it back in 2061.
• A small change in trajectory can save months of flying time.

The passage of a small object across the face of a larger one.

• A transit of Mercury across the Sun happens only about thirteen times each century.
• Astronomers find exoplanets by spotting the tiny dip of a transit in starlight.
• During the transit, the small shadow of the moon crossed the clouds of Jupiter.

Describing invisible light beyond violet, the kind that causes sunburn.

• The Sun sends both visible light and ultraviolet rays to Earth.
• Bees can see ultraviolet patterns on flowers.
• Ultraviolet pictures of the Sun show hot flares in false color.

The darkest, central part of a shadow.

• During a total eclipse, the small dark umbra of the Moon sweeps across Earth.
• Stand inside the umbra, and the Sun disappears completely.
• The core of a sunspot is called its umbra.

Everything that exists: all of space, time, stars, and galaxies.

• The universe began about 13.8 billion years ago.
• Astronomers estimate that the universe holds trillions of galaxies.
• Is there another Earth somewhere in the universe?

The seventh planet from the Sun, an ice giant tipped on its side.

• Uranus spins on its side as it travels around the Sun.
• The blue-green color of Uranus comes from methane high in its air.
• William Herschel discovered Uranus in 1781.

A completely empty space with no air at all.

• Sound cannot travel through the vacuum of space.
• In the vacuum of space, water would boil at once.
• Astronauts must carry their own air because space is a vacuum.

Two doughnut-shaped zones of fast particles trapped by the magnetic field of Earth.

• The Van Allen belts catch fast particles that arrive from the Sun.
• Spacecraft passing through the Van Allen belts need extra shielding.
• James Van Allen discovered the belts in 1958.

The hottest planet and the closest neighbor of Earth, wrapped in thick clouds.

• Venus shines brighter than every star in our night sky.
• The clouds of Venus are made of tiny drops of acid.
• A day on Venus lasts longer than its year.

The spring equinox, when the Sun crosses the equator and the days grow longer.

• The vernal equinox marks the first day of spring.
• The date of Easter is set from the vernal equinox.
• At the vernal equinox, the Sun rises almost due east.

The small slice of light that human eyes can see, from red to violet.

• Visible light is only a tiny slice of all the light in the universe.
• A rainbow splits visible light into its colors.
• Our eyes catch visible light, but not radio waves or X-rays.

Two NASA probes, launched in 1977, that are now flying through interstellar space.

• Voyager 1 is the farthest human-made object from Earth.
• The Voyager probes carry golden records with sounds and music from Earth.
• Voyager 2 is still the only spacecraft to have visited Uranus and Neptune.

Describing the Moon as it appears to shrink after the full moon.

• The waning moon rose later every night.
• A waning crescent hung low in the sky before dawn.
• After the full moon, the waning phases begin.

The distance between the top of one wave and the top of the next.

• Red light has a longer wavelength than blue light.
• Radio waves have the longest wavelength of all light.
• Astronomers study every wavelength to understand the universe.

Describing the Moon as it appears to grow toward the full moon.

• During the waxing nights, the lit side of the Moon grows on the right.
• The waxing gibbous moon shines high in the evening.
• Farmers once planted certain crops under the waxing moon.

The floating feeling you have when gravity seems to disappear.

• Astronauts enjoy weightlessness as they float through the station.
• Weightlessness makes even pouring water a funny challenge.
• On special flights, riders feel weightlessness for about half a minute at a time.

The tiny, super-dense leftover core of a star like the Sun.

• A white dwarf packs a star into a ball the size of Earth.
• Sirius B is a white dwarf that orbits the brightest star in our night sky.
• A teaspoon of white dwarf material would weigh several tons.

An imagined shortcut through space and time, loved in science fiction.

• In the movie, the crew flew through a wormhole to a far galaxy.
• No one has ever seen a real wormhole.
• The math of Einstein allows wormholes, but nobody knows if they exist.

A high-energy invisible light that can pass through soft materials.

• Special telescopes in space catch X-rays from matter falling into black holes.
• Doctors use X-rays to photograph the bones inside your body.
• The Sun sends out X-rays during big flares.

The time a planet takes to circle its star once.

• One year on Earth lasts about 365 and a quarter days.
• A year on Mercury lasts only 88 Earth days.
• Neptune needs 165 Earth years to finish one year.

The ordinary type of star that our Sun belongs to.

• Our Sun is a yellow dwarf in the middle of its life.
• Yellow dwarfs like the Sun shine for around ten billion years.
• Despite the name, a yellow dwarf is still a huge ball of burning gas.

The point in the sky directly above your head.

• At noon in the tropics, the Sun can come close to the zenith.
• The meteor faded just past the zenith.
• A star crossing the zenith appears at its brightest.

The band of twelve constellations that the Sun seems to visit during the year.

• The Moon and the planets always travel through the zodiac.
• Astrology names twelve signs after the zodiac constellations.
• The zodiac runs along the ecliptic.

A faint triangle of glow along the ecliptic, made by sunlight shining on space dust.

• On dark desert nights, you may spot the zodiacal light after sunset.
• Ancient watchers called the zodiacal light the false dawn.
• Zodiacal light comes from dust shed by comets.