• Guided Tours
  • Welcome Tour
    • • A guided introduction to Starry Night.
    • • A quick tour
      • The Keys to the cosmic clockwork
      • Signposts in the sky
      • Explore ancient lunar craters
      • Find all the planets
      • Your virtual telescope
      • Catch a comet after sunset
      • Follow an asteroid
      • Zoom in on deep space objects
      • Prepare for celestial events
      • Share the view
      • Travel back in time
      • Forecast the Sun's disappearance
      • Stargaze from any location on Earth
      • Leave Earth behind
      • Rendezvous with the ISS
      • Stargaze from anywhere in the solar system
      • Explore Mars
      • Sail easily around in space
      • Go anywhere, anytime
      • Observe planets from their moons
      • Where no probe has gone before
      • Hitch a lift on a comet
      • Visit the neighbors
      • Travel to an alien world
      • Escape the Milky Way
      • Check out the galaxies
      • Escape to the edge of known space and time
      • Take control
  • Sky Calendar
  • Live Space News
  • Learning Moments
    • The 2024 Total Solar Eclipse
      • • Guiding Question: What causes a solar eclipse, and where and how and where can I safely observe the next one?
      • • Key Concepts
        • A solar eclipse is caused by a Sun-Moon-Earth alignment in which the Moon blocks light from the Sun causing a shadow to appear on the Earth.
        • The next solar eclipse visible in North America will occur on April 8, 2024; this eclipse will actually be visible in almost all of North America.
      • • 1: What is a Solar Eclipse?
        • 2: The Total Solar Eclipse of 2024
        • 3: Safely Watching the Eclipse
        • 4: Solar Eclipse Math
        • 5: Solar Eclipses in History
        • 6: The Saros Cycle
    • The 2017 Total Solar Eclipse
      • • Guiding Question: Where and how do I safely view the 2017 total solar eclipse?
      • • Key Concepts
        • A solar eclipse is caused by the Moon blocking the light of the Sun and casting a small shadow on the Earth.
        • There will be a total solar eclipse visible in the contiguous United States on August 21, 2017.
      • • 1: What is a Solar Eclipse?
        • 2: The Total Solar Eclipse of 2017
        • 3: Safely Watching the Eclipse
        • 4: Solar Eclipse Math
        • 5: Solar Eclipses in History
        • 6: The Saros Cycle
    • Exploring the TRAPPIST-1 Planetary System
      • • Guiding Question: Why is the discovery of the TRAPPIST-1 planetary system significant?
      • • Key Concepts
        • An exoplanet is a planet that orbits a star outside of our own solar system.
        • The habitable zone is a region in space around a star that could conceivably support life.
        • Red dwarf stars (which outnumber sun-like stars) also have Earth-sized exoplanets.
      • • 1: A Significant Discovery
        • 2: Detecting TRAPPIST-1 Exoplanets
        • 3: Habitability
        • 4: The TRAPPIST-1 System
        • 5: TRAPPIST-1 Star
        • 6: The Planets
        • 7: TRAPPIST-1b
        • 8: TRAPPIST-1c
        • 9: TRAPPIST-1d
        • 10: TRAPPIST-1e
        • 11: TRAPPIST-1f
        • 12: TRAPPIST-1g
        • 13: TRAPPIST-1h
        • 14: Living on a TRAPPIST-1 Planet
        • 15: Next Steps
    • Exoplanets: Worlds Outside Our Solar System
      • • Guiding Question: What can be learned about planets outside of our own solar system?
      • • Key Concepts
        • An exoplanet is a planet that orbits a star outside of our own solar system.
        • Over 1,900 confirmed exoplanets have already been discovered by a variety of methods.
        • The habitable zone is a region in space around a star that could conceivably support life.
      • • 1: What Is an Exoplanet?
        • 2: Detecting Exoplanets I – Radial Velocity
        • 3: Detecting Exoplanets II – Transit Photometry
        • 4: Detecting Exoplanets III – Direct Imaging
        • 5: Detecting Exoplanets IV – Gravitational Microlensing
        • 6: The Habitable Zone I – Temperatures of Exoplanets
        • 7: The Habitable Zone II – Habitable Zones and Stellar Luminosity
        • 8: Properties of Exoplanets – Exoplanet Classification
  • Quick Find
    • • The Stars
      • The Constellations
      • Naked Eye Objects
      • Objects for Binoculars
      • Your Birthday Star
  • First Night Out
    • Finding Your Way Around
      • • Introduction
        • The Big Dipper
        • Star hopping
        • Learning the sky
    • Measuring Distances
      • • Distances
        • Calibrating with the Big Dipper
    • Measuring Brightness
      • • Introduction
        • The magnitude scale
        • Where do objects fit in the magnitude scale?
        • A few handy terms
    • The Ecliptic and the Zodiac
      • • Introduction
        • The ecliptic
        • The Zodiac
        • Crossing the ecliptic
    • The Names of Stars
      • • Introduction
        • Common names
        • The Bayer system
        • The Flamsteed system
        • Catalog names
        • Naming your own star
    • The Seasons
      • • Introduction
        • The Earth's Tilt
        • The first day of spring
        • The first day of summer
        • The first day of autumn
        • The first day of winter
        • The four seasons
    • How Long is a Day?
      • • Introduction
        • When in time
        • Solar day versus sidereal day
        • Where in space
        • The rotation of the night sky
        • Changing your latitude
        • Latitude 45 degrees north
        • Latitude 60 degrees north
        • At the North Pole
        • At the equator
        • Latitude 30 degrees south
        • At the South Pole
        • Same day, different view
    • How Long is a Year?
      • • Introduction
        • Measuring revolution
        • Don't forget precession
        • Seasonal changes in the stars and planets
        • The sun in the constellations
    • What's Your Sign?
      • • Introduction
        • The constellations of the Zodiac
        • Precession and astrology
        • The precession of the equinoxes
        • Your real sign
    • The Astronomical Coordinate Systems
      • • The local coordinate system
        • How high is it?
        • The equatorial coordinate system
        • The celestial grid
        • Determining right ascension
        • The vernal equinox
    • Little Dipper and Sky Darkness
      • • The Little Dipper
        • Precession
        • Polaris and latitude
        • Guardian stars
    • The Steps to Rewarding Stargazing
      • • Introduction
        • Set a goal
        • Set a date
        • Find a suitable observing site
        • Dress warmly
        • Get there early
        • Plan and pack for comfort
        • Start simple
        • Get binoculars
        • Move up to a telescope
        • Join an astronomy club
        • Bring refreshments
        • Prepare for the unexpected
        • Record your observations
    • Star Party Survival Guide
      • • Introduction
        • Come prepared
        • What to wear
        • Children welcome
        • When to arrive
        • Bright lights, big no-no
        • Observing at a star party
        • Leaving a star party
        • Enjoying the experience
  • Our Solar System
    • Our Solar System
      • • Introduction
        • The wanderers
        • Inner worlds, outer worlds, and worlds beyond
        • Remarkably flat
        • Balls of rock and ice
        • One of many
        • A scale model
        • Origins
        • Bode's Law
    • The Zodiacal Light
      • • Introduction
        • What it is
        • When to see it
        • What it looks like
        • Finer points to look for
    • The Sun
      • • Introduction
        • Our Sun, the star
        • What is it made of?
        • Bobbing around the Milky Way
        • Sunspots
        • Flares and prominences
    • The Sunspot Cycle
      • • Introduction
        • Past disruptions
    • Solar Eclipses
      • • Introduction
        • When the Moon blocks the Sun
        • Why do eclipses happen?
        • Partial eclipses
        • Annular eclipses
        • Total eclipses
        • The last eclipse
    • Auroras and Solar Storms
      • • A glow in the sky
        • A colorful tapestry
    • Mysteries of the Sun
      • • Introduction
        • The flat Sun
        • Debunking a myth
        • Solar pillars and the green flash
    • Artificial Satellites
      • • Introduction
        • Is it a bird...?
        • A swarm of gnats
        • Light-reflecting beacons
        • Likely targets
        • Standing still
        • Low-Earth orbit
        • Satellite spotting
        • Best of class
        • A flare for Iridium
        • Tumbling around the planet
        • What goes up...
        • A fiery end
    • Meteor Showers
      • • Introduction
        • Falling stars
        • Cleaning up after the comet
        • Observing a meteor shower
        • Meteor, meteoroid, or meteorite?
    • The Moon
      • • Introduction
        • Our neighbor
        • The face of antiquity
        • On the ground
        • Highlands and maria
        • The Man in the Moon
        • Earthshine
        • A peek at the far side
        • The Moon's effect on Earth
        • Turnabout is fair play
        • The Moon Illusion
        • The Moon through binoculars
        • Moon occultation
        • Origins
    • The Phases of the Moon
      • • Introduction
        • The lunar cycle
        • Geometry
    • Lunar Eclipses
      • • Introduction
        • Casting a shadow on the Moon
        • The view from the Moon
        • Types of lunar eclipses
    • Full Moon Names
      • • Introduction
        • Cool lunar-cycle facts
        • The wolf moon in January
        • The snow moon in February
        • The worm moon in March
        • The pink moon in April
        • The flower moon in May
        • The strawberry moon in June
        • The buck moon in July
        • The sturgeon moon in August
        • The harvest moon in September
        • The hunter’s moon in October
        • The beaver moon in November
        • The cold moon in December
    • Top Ten Moon Facts
      • • Introduction
        • Bye bye Moon
        • Ocean tug
        • Planet Moon
        • Moonquakes
        • Egghead
        • Sister moons
        • Punching bag
        • Moon trees
        • Locked in orbit
        • Making of the Moon
    • The Day the Moon Was Made
      • • Introduction
        • Twenty-four hours of chaos
        • Case is not airtight
        • Other ways the Moon might form
    • The Planets: Mercury
      • • Introduction
        • Messenger of the gods
        • A cratered surface
        • A hot and cold world
        • A visit by Mariner
        • Observing Mercury
        • A fast little world
        • The best time to see Mercury
        • A Mercury transit
    • The Planets: Venus
      • • Introduction
        • A greenhouse world
        • Retrograde motion
        • A view from the surface
        • Visitors from Earth
        • Observing venus
        • A transit of Venus
    • The Planets: Earth
      • • Introduction
        • Our home
        • A view from space
    • The Planets: Mars
      • • Introduction
        • The red planet
        • A smaller world
        • Two tiny moons
        • Riddles in the rusty dust
        • Olympus Mons
        • Valles Marineris
        • The martian seasons
        • Is there life on Mars?
        • On the surface
        • Robots to Mars
        • Observing Mars
        • Mars through a telescope
    • The Planets: Jupiter
      • • Introduction
        • The king of planets
        • A light heavyweight
        • Jupiter’s moons
        • A solar system in miniature
        • The gasworks
        • The Great Red Spot
        • A fast spinner
        • A comet comes to call
        • The phenomena of the moons
        • A voyage of discovery
    • The Planets: Saturn
      • • Introduction
        • Lord of the Rings
        • What’s it made of?
        • Saturn’s largest moon
        • Saturn’s smaller moons
        • Observing Saturn
        • You are there!
    • The Planets: Uranus
      • • Introduction
        • The first planet discovered with a telescope
        • What’s it made of?
        • Tilt! Tilt!
        • The moons of Uranus
        • Observing Uranus
    • The Planets: Neptune
      • • Introduction
        • The strange case of Neptune
        • Predicted before it was seen
        • The mystery is solved
        • The other blue planet
        • Voyager passes by
        • The moons of Neptune
        • Observing Neptune
    • Dwarf Planets and Pluto
      • • Introduction
        • A remote world
        • A needle in a haystack
        • Dwarf planet, big comet, or icy asteroid?
        • Pluto’s sidekick
        • Pluto through the eyes of Hubble
        • Observing Pluto and Ceres
    • Planetary Motions
      • • Introduction
        • Earth centric
        • Retrograde motion
        • Sun centric
        • Brahe and Kepler
        • Galileo and the telescope
        • Sir Isaac Newton
        • General relativity
    • The Moons of Planets
      • • Introduction
        • The moons of Mercury and Venus
        • The moons of Earth
        • The moons of Mars
        • The moons of Jupiter
        • The moons of Saturn
        • The moons of Uranus
        • The moons of Neptune
        • The moons of dwarf planet Pluto
    • The Asteroids
      • • Introduction
        • Chunks of rock and metal
        • The Main Belt
        • The Kuiper Belt
        • The Centaurs
        • Captured asteroids
        • Phobos and Deimos
        • Asteroid reservoirs
        • Close to home
        • Too close for comfort
        • Observing an asteroid
    • The Comets
      • • Introduction
        • A dirty snowball
        • A tale of two tails
        • Eyes on the sky
        • A historic “hairy star”
        • A recent visitor
        • A close encounter
  • Stars & Exoplanets
    • The Stars
      • • Introduction
        • A cloudy beginning
        • A fusion reactor
        • Possible outcomes
        • Star colors
        • Multiple stars
        • Variable stars
    • Planets Around Other Stars
      • • Introduction
        • Detecting extrasolar planets
        • Strange new worlds
        • Visiting these planets
    • Shape-Shifting Constellations
      • • Introduction
        • A matter of distance
        • From Alpha Centauri
        • Proper motion
        • Barnard’s Star
        • 100,000 years from tonight
  • Our Galaxy & Beyond
    • Our Galaxy
      • • Introduction
        • A river of light
        • Our solar system in the Milky Way
        • From the inside, looking out
        • A stellar hurricane
        • A closer look at the structure
        • Just how big is it?
        • A journey to the center of the galaxy
        • The Milky Way is born
        • ...and grows
    • Nebulae
      • • Introduction
        • Dark nebulae
        • Bright nebulae
    • Supernovae
      • • Introduction
        • An ancient mystery
        • A cataclysmic explosion
        • Type 2 supernova
        • As bright as a galaxy
        • Type 1 supernova
        • A helping hand
        • A white dwarf collapses
        • A beautiful sight
    • Neutron Stars and Black Holes
      • • Introduction
        • Neutron stars
        • Black holes
    • Other Galaxies
      • • Introduction
        • The Local Group
        • Dwarf galaxies
        • Our closest neighbor
        • Headed for collision
        • Observing the Local Group galaxies
    • Giant Leaps
      • • Introduction
        • 1 m
        • 10 m
        • 100 m
        • 1000 m
        • 10 km
        • 100 km
        • 1,000 km
        • 10,000 km
        • 100,000 km
        • 1,000,000 km
        • 10,000,000 km
        • 100,000,000 km
        • 1,000,000,000 km
        • 10,000,000,000 km
        • 100,000,000,000 km
        • 1,000,000,000,000 km
        • 10,000,000,000,000 km
        • 100,000,000,000,000 km
        • 1,000,000,,000,000,000 km
        • 10,000,000,000,000,000 km
        • 100,000,000,000,000,000 km
        • 1,000,000,000,000,000,000 km
        • 10,000,000,000,,000,000,000 km
        • 100,000,000,000,000,000,000 km
        • 1,000,000,000,000,000,000,000 km
        • 10,000,000,000,000,000,000,000 km
        • Sightseeing
        • 100,000,000,000,000,000,000,000 km
  • Space Missions
    • Space Missions - New Horizons
      • • Introduction
        • Mission Timeline
        • The Science Payload
        • Pluto Encounter Day
        • Beyond Pluto
    • Space Missions - Voyager 2
      • • Introduction
        • Overview
        • Launch
        • Jupiter encounter
        • Saturn encounter
        • Neptune encounter
        • Ad Astra...
    • Space Missions - Cassini/Huygens
      • • Introduction
        • Overview
        • Cassini at Saturn
        • Saturn flybys
        • Encounter with Titan
        • The Huygens Mission
    • Space Missions - Galileo
      • • Introduction
        • Launch
        • First flyby of an asteroid
        • First discovery of an asteroid moon
        • Galileo arrives at Jupiter
        • Oceans on Europa
        • Closest flyby of Io
        • Closest Flyby of Europa
        • Impact into Jupiter
    • Moon Missions - Apollo 8
      • • Introduction
        • Launch into Earth orbit
        • Trans-lunar Injection - on the way to the Moon
        • A look back at the Earth
        • Leaving the Earth
        • Taking star measurements
        • Television of the Earth
        • Approaching the Moon
        • Into lunar orbit
        • Earthrise
        • Trans Earth Injection - and a look back at the Moon
        • Approaching the Earth
        • Service module separation and entry
    • Moon Missions - Apollo 10
      • • Introduction
        • Launch into Earth orbit
        • Trans-lunar Injection - on the way to the Moon
        • A look back at the Earth
        • A view of Europe and Africa in Sagittarius
        • Approaching the Moon
        • Into lunar orbit
        • Activities in lunar orbit
        • Trans Earth Injection - and a look back at the Moon
        • Approaching the Earth
    • Moon Missions - Apollo 11
      • • Introduction
        • Launch into Earth orbit
        • Trans-lunar Injection - on the way to the Moon
        • Looking back at the Earth
        • Approaching the Moon - an eerie eclipse
        • Into Lunar Orbit
        • The Eagle has landed
        • On the Moon
        • Blasting off the Moon back into orbit
        • Leaving lunar orbit for home
        • Looking back at the Moon
        • Approaching the Earth
        • Mission Success
    • Moon Missions - Apollo 12
      • • Introduction
        • Launch into Earth orbit
        • Trans-lunar Injection - on the way to the Moon
        • Looking back at the Earth
        • Approaching the Moon
        • Into Lunar Orbit
        • Lunar Landing
        • On the Moon
        • Blasting off the Moon back into orbit
        • Leaving lunar orbit for home
        • Looking back at the Moon
        • Approaching the Earth - an Eclipse of the Sun by the Earth
        • Mission Success
    • Moon Missions - Apollo 13
      • • Introduction
        • Launch into Earth orbit
        • Trans-lunar Injection - on the way to the Moon
        • View of the Earth
        • The accident
        • Around the Moon
        • Looking back at the Moon
        • The Service Module
        • The Lunar Module
        • Lessons learned
    • Moon Missions - Apollo 14
      • • Introduction
        • Launch into Earth orbit
        • Trans-lunar Injection
        • Approaching the Moon
        • Into Lunar Orbit
        • Landing at Fra Mauro
        • Lunar surface activities
        • Lunar Ascent
        • Leaving lunar orbit for home
        • Back on track
    • Moon Missions - Apollo 15
      • • Introduction
        • Launch into Earth orbit
        • Trans-lunar Injection
        • The Earth from 46 000 km
        • Into Lunar Orbit
        • Landing at Hadley Rille
        • Lunar surface activities
        • Lunar ascent
        • Leaving lunar orbit for home
        • Spacewalk
        • A lunar eclipse from space
        • Another success
    • Moon Missions - Apollo 16
      • • Introduction
        • Launch into Earth orbit
        • Trans-lunar Injection
        • Looking back at Earth
        • Into Lunar Orbit
        • Landing at Descartes
        • Lunar surface activities
        • Lunar ascent
        • Leaving lunar orbit for home
        • Looking back at the Moon
        • Mattingly EVA
        • The second last mission
    • Moon Missions - Apollo 17
      • • Introduction
        • Launch into Earth orbit
        • Trans-lunar Injection
        • The full Earth
        • Into Lunar Orbit
        • Landing at Taurus Littrow
        • Lunar surface activities
        • Lunar ascent
        • Leaving lunar orbit for home
        • A last view at the Moon
        • Spacewalk
        • We will return
  • Night Sky Tours
    • The Spring Sky
      • • Introduction
        • Your celestial guidepost
        • Arc to Arcturus...
        • ...and speed on to Spica
        • The prominent constellation of spring
        • A beehive of stars
    • The Summer Sky
      • • Introduction
        • The Summer Triangle
        • The harp of the gods
        • The eagle of Zeus
        • The Northern Cross
        • The strong man of the heavens
        • The summer Milky Way
        • Gazing inward
    • The Autumn Sky
      • • Introduction
        • Let the W guide you
        • The Demon Star
        • A double cluster
        • The Square of Pegasus
        • The most distant naked-eye object
        • King Cepheus
        • The Southern Fish
        • A great time for meteor showers
        • A remnant of summer
    • The Winter Sky
      • • Introduction
        • A mighty hunter
        • The stars of Orion
        • The belt of Orion
        • The jewel of Orion
        • The Dog Star
        • Before the dog
        • The Seven Sisters
        • The Twins
        • The Charioteer
    • The Sky Down Under
      • • Introduction
        • The other half of the celestial sphere
        • The not-so-familiar stars
        • The Southern Cross
        • A void in the Milky Way
        • The closest star
        • A blazing ball of stars
        • The greatest nebula
        • The Large Magellanic Cloud
        • The Small Magellanic Cloud
    • Other Patterns in the Sky
      • • Introduction
        • The Kids
        • The Teapot
        • The Sickle
        • The Summer Triangle
        • The Seven Sisters
        • The Great Square of Pegasus
        • The Sword of Orion
        • The Coathanger Cluster
        • The Southern Cross
        • The Belt of Orion
        • The Bull of Poniatowski
        • The Diamond of Virgo
        • The False Cross
        • The Fish Hook
        • The Sail
        • The Ice Cream Cone
        • The Pointers
        • The Northern Fly
        • The Y of Aquarius
        • Big Dipper or the Plough
        • The Three Patriarchs
        • The Asses and the Manger
        • The Circlet
        • The Whale’s Head
        • The Little Dipper
        • Job’s Coffin
        • The Keystone
        • The W or the Chair
        • The Hyades
    • The Messier Objects
      • • Introduction
        • In search of a comet
        • Planetary nebula
        • Star clusters
        • Diffuse nebula
        • Galaxies
        • A starting point
    • The Messier Marathon
      • • Introduction
        • Messier order
    • Twenty Great Fuzzies
      • • Introduction
        • The Eta Carinae Nebula
        • The Great Orion Nebula
        • The Andromeda Galaxy
        • Omega Centauri
        • The Great Hercules Cluster
        • The Large Magellanic Cloud
        • The Pleiades
        • NGC 6231
        • The Double Cluster
        • The Small Magellanic Cloud
        • The Ring Nebula
        • The Bode’s and Cigar Galaxies
        • The Whirlpool Galaxy
        • The Lagoon Nebula
        • The Beehive Cluster
        • The Crab Nebula
        • The Rosette Nebula
        • A galactic glutton
        • The Eagle nebula
        • The Triangulum Galaxy
        • Keep Digging!
    • Ten Great Stars
      • • Introduction
        • Sirius
        • Canopus
        • Alpha Centauri
        • Arcturus
        • Vega
        • Capella
        • Rigel
        • Procyon
        • Achernar
        • Betelgeuse
  • Glossary