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[[File:lighterstill.jpg]][[File:Milky_way_galaxy.jpg|right|frame]]
[[File:lighterstill.jpg]][[File:Milky_way_galaxy.jpg|right|frame]]
==Etymology==
The [[word]] '''galaxy''' derives from the [[Greek]] term for our own galaxy, galaxias (γαλαξίας), or kyklos galaktikos, meaning "milky [[circle]]" for its appearance in the sky. In Greek [[mythology]], Zeus places his son born by a [[mortal]] woman, the infant Heracles, on Hera's breast while she is asleep so that the baby will drink her divine milk and will thus become [[immortal]]. Hera wakes up while breastfeeding and then realizes she is nursing an unknown baby: she pushes the baby away and a jet of her milk sprays the night sky, producing the faint band of light known as the [[Milky Way]].
In the astronomical [[literature]], the capitalized word 'Galaxy' is used to refer to our galaxy, the [[Milky Way]], to distinguish it from the billions of other galaxies. The term Milky Way first appeared in the [[English]] [[language]] in a [[poem]] by [http://en.wikipedia.org/wiki/Geoffrey_Chaucer Chaucer].
:: "See yonder, lo, the Galaxyë
:: Which men clepeth the Milky Wey,
::For hit is whyt."
:::—Geoffrey Chaucer. The House of Fame, c. 1380.
When [http://en.wikipedia.org/wiki/William_Herschel William Herschel] constructed his catalog of deep sky objects, he used the name [http://en.wikipedia.org/wiki/Spiral_nebula spiral nebula] for certain objects such as M31. These would later be recognized as immense conglomerations of [[stars]], when the true distance to these objects began to be appreciated, and they would be termed island universes. However, the [[word]] [[Universe]] was understood to mean the entirety of [[existence]], so this expression fell into disuse and the objects instead became known as galaxies.
==Description==
A '''galaxy''' is a massive, [[gravity|gravitational]]ly bound [[system]] that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed [http://en.wikipedia.org/wiki/Dark_matter dark matter]. The name is from the Greek root galaxias [γαλαξίας], meaning "milky," a reference to the [http://en.wikipedia.org/wiki/Milky_Way Milky Way] galaxy. Typical galaxies range from dwarfs with as few as ten million (107) stars up to giants with one trillion (10¹²) stars, all orbiting the galaxy's center of [[mass]]. Galaxies can also contain many multiple star systems, star clusters, and various interstellar clouds. The [[Sun]] is one of the stars in the Milky Way galaxy; the Solar System includes the Earth and all the other objects that orbit the Sun.
A '''galaxy''' is a massive, [[gravity|gravitational]]ly bound [[system]] that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed [http://en.wikipedia.org/wiki/Dark_matter dark matter]. The name is from the Greek root galaxias [γαλαξίας], meaning "milky," a reference to the [http://en.wikipedia.org/wiki/Milky_Way Milky Way] galaxy. Typical galaxies range from dwarfs with as few as ten million (107) stars up to giants with one trillion (10¹²) stars, all orbiting the galaxy's center of [[mass]]. Galaxies can also contain many multiple star systems, star clusters, and various interstellar clouds. The [[Sun]] is one of the stars in the Milky Way galaxy; the Solar System includes the Earth and all the other objects that orbit the Sun.
