Galilean moons

Galilean satellitesGalilean moonmoons of JupiterGalilean satellitefour largest moonsmoonssatellitesGalileanJupiter's moonsMedician stars
The Galilean moons (or Galilean satellites) are the four largest moons of Jupiter—Io, Europa, Ganymede, and Callisto.wikipedia
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Moons of Jupiter

moon of JupiterJovian systemJupiter's moons
The Galilean moons (or Galilean satellites) are the four largest moons of Jupiter—Io, Europa, Ganymede, and Callisto.
The most massive of the moons are the four Galilean moons, which were independently discovered in 1610 by Galileo Galilei and Simon Marius and were the first objects found to orbit a body that was neither Earth nor the Sun.

Io (moon)

IoAtmosphere of IoIo torus
The Galilean moons (or Galilean satellites) are the four largest moons of Jupiter—Io, Europa, Ganymede, and Callisto.
Io (Jupiter I) is the innermost and third-largest of the four Galilean moons of the planet Jupiter.

Europa (moon)

EuropaEuropanLife on Europa
The Galilean moons (or Galilean satellites) are the four largest moons of Jupiter—Io, Europa, Ganymede, and Callisto.
Europa (, Jupiter II) is the smallest of the four Galilean moons orbiting Jupiter, and the sixth-closest to the planet of all the 79 known moons of Jupiter.

Ganymede (moon)

GanymedeNicholson RegioAtmosphere of Ganymede
The Galilean moons (or Galilean satellites) are the four largest moons of Jupiter—Io, Europa, Ganymede, and Callisto. A Chinese historian of astronomy, Xi Zezong, has claimed that a "small reddish star" observed near Jupiter in 362 BCE by Chinese astronomer Gan De may have been Ganymede, if true, might predate Galileo's discovery by around two millennia.
Outward from Jupiter, it is the seventh satellite and the third of the Galilean moons, the first group of objects discovered orbiting another planet.

Callisto (moon)

CallistoAtmosphere of Callistofourth Galilean moon of Jupiter
The Galilean moons (or Galilean satellites) are the four largest moons of Jupiter—Io, Europa, Ganymede, and Callisto.
At 4821 km in diameter, Callisto has about 99% the diameter of the planet Mercury but only about a third of its mass. It is the fourth Galilean moon of Jupiter by distance, with an orbital radius of about 1883000 km.

Galileo Galilei

GalileoGalileanGalilei
They were first seen by Galileo Galilei in December 1609 or January 1610, and recognized by him as satellites of Jupiter in March 1610.
His contributions to observational astronomy include the telescopic confirmation of the phases of Venus, the observation of the four largest satellites of Jupiter, the observation of Saturn's rings, and the analysis of sunspots.

Orbital resonance

1:1 resonanceresonancemean-motion resonance
The three inner moons—Io, Europa, and Ganymede—are in a 4:2:1 orbital resonance with each other.
It was Laplace who found the first answers explaining the linked orbits of the Galilean moons (see below).

Simon Marius

[Simon] MayrMarius, SimonMundus Iovialis
Galileo initially named his discovery the Cosmica Sidera ("Cosimo's stars"), but the names that eventually prevailed were chosen by Simon Marius.
He is most noted for making the first observations of the four largest moons of Jupiter, before Galileo himself, and his publication of his discovery led to charges of plagiarism.

Sidereus Nuncius

Starry MessengerThe Starry MessengerSidereus Nuncius (The Starry Messenger)
Galileo's Sidereus Nuncius (Starry Messenger), which announced celestial observations through his telescope, does not explicitly mention Copernican heliocentrism, a theory that placed the Sun at the center of the universe.
It was the first published scientific work based on observations made through a telescope, and it contains the results of Galileo's early observations of the imperfect and mountainous Moon, the hundreds of stars that were unable to be seen in either the Milky Way or certain constellations with the naked eye, and the Medicean Stars (later Galilean moons) that appeared to be circling Jupiter.

Planet

planetsFormer classification of planetsplanemo
They are among the largest objects in the Solar System with the exception of the Sun and the eight planets, with radii larger than any of the dwarf planets.
Some large satellites (moons) are of similar size or larger than the planet Mercury, e.g. Jupiter's Galilean moons and Titan.

Gan De

A Chinese historian of astronomy, Xi Zezong, has claimed that a "small reddish star" observed near Jupiter in 362 BCE by Chinese astronomer Gan De may have been Ganymede, if true, might predate Galileo's discovery by around two millennia.
By occluding Jupiter itself behind a high tree limb perpendicular to the satellites' orbital plane to prevent the planet's glare from obscuring them, one or more of the Galilean moons might be spotted in favorable conditions.

Johannes Kepler

KeplerDioptriceJohan Kepler
Marius discovered the moons independently at nearly the same time as Galileo, 8 January 1610, and gave them their present names, derived from the lovers of Zeus, which were suggested by Johannes Kepler, in his Mundus Jovialis, published in 1614.
Though it explicitly extended the first two laws of planetary motion (applied to Mars in Astronomia nova) to all the planets as well as the Moon and the Medicean satellites of Jupiter, it did not explain how elliptical orbits could be derived from observational data.

Sulfur dioxide

sulphur dioxideSO 2 SO2
Io has an extremely thin atmosphere made up mostly of sulfur dioxide (SO 2 ).
As an ice, it is thought to exist in abundance on the Galilean moons—as subliming ice or frost on the trailing hemisphere of Io, and in the crust and mantle of Europa, Ganymede, and Callisto, possibly also in liquid form and readily reacting with water.

List of natural satellites

eighth-largest moonlargestList of moons
They are among the largest objects in the Solar System with the exception of the Sun and the eight planets, with radii larger than any of the dwarf planets.
The earliest published discovery of a moon other than the Earth's was by Galileo Galilei, who discovered the four Galilean moons orbiting Jupiter in 1610.

Giovanni Domenico Cassini

Giovanni CassiniCassiniJean Dominique Cassini
The method was used by Cassini and Picard to re-map France.
Cassini was also the first to make successful measurements of longitude by the method suggested by Galileo, using eclipses of the Galilean satellites as a clock.

Extraterrestrial life

alienextraterrestrialaliens
The apparent youth and smoothness of the surface have led to the hypothesis that a water ocean exists beneath it, which could conceivably serve as an abode for extraterrestrial life.
Scientists have indications that heated subsurface oceans of liquid water may exist deep under the crusts of the three outer Galilean moons—Europa, Ganymede, and Callisto.

Jupiter's moons in fiction

AmaltheaCallistoEuropa
Jupiter's extensive system of natural satellites – in particular the four large Galilean moons (Io, Europa, Ganymede and Callisto) – has been a common science fiction setting.

Celatone

The main problem with the technique was that it was difficult to observe the Galilean moons through a telescope on a moving ship; a problem that Galileo tried to solve with the invention of the celatone.

Tidal heating

tidal flexingtidally heatedtidally heating
Heat energy from tidal flexing ensures that the ocean remains liquid and drives geological activity.
Io's eccentricity persists as the result of its orbital resonances with the Galilean moons Europa and Ganymede.

Europa (consort of Zeus)

EuropaThe Rape of EuropaEuropa (mythology)
The name comes from a mythical Phoenician noblewoman, Europa, who was courted by Zeus and became the queen of Crete, though the name did not become widely used until the mid-20th century.
The smallest of Jupiter's Galilean moons was named after Europa.

Binoculars

binocularfield glassesfield glass
(They are, however, easily distinguished with even low-powered binoculars.) They have apparent magnitudes between 4.6 and 5.6 when Jupiter is in opposition with the Sun, and are about one unit of magnitude dimmer when Jupiter is in conjunction.
A number of solar system objects that are mostly to completely invisible to the human eye are reasonably detectable with medium-size binoculars, including larger craters on the Moon; the dim outer planets Uranus and Neptune; the inner "minor planets" Ceres, Vesta and Pallas; Saturn's largest moon Titan; and the Galilean moons of Jupiter.

Meudon Great Refractor

Grande LunetteGrande Lunette'' (83-cm Great Refractor)great refractor of Meudon
In the early 20th century, the angular sizes of the Galilean satellites were measured with the Meudon Great Refractor.
In the early 20th century, the Meudon refractor was noted for being very steady, and this aided in taking micrometer measurements of the Galilean moons of Jupiter.

Solar System

outer Solar Systeminner Solar Systemouter planets
They are among the largest objects in the Solar System with the exception of the Sun and the eight planets, with radii larger than any of the dwarf planets.

Sun

solarSolThe Sun
Galileo's Sidereus Nuncius (Starry Messenger), which announced celestial observations through his telescope, does not explicitly mention Copernican heliocentrism, a theory that placed the Sun at the center of the universe. They are among the largest objects in the Solar System with the exception of the Sun and the eight planets, with radii larger than any of the dwarf planets.

Dwarf planet

dwarf planetsList of dwarf planetsplanet
They are among the largest objects in the Solar System with the exception of the Sun and the eight planets, with radii larger than any of the dwarf planets.