Year of 2017

Billions and Billions
The Milky Way over the Atlantic Ocean

Get away from the artificial lights of cities and other modern human settlements and you’ll see just how fantastically bright the night sky can be. It was the stars that make up our own galaxy—between 100 and 400 billion of them—that the ancient Greeks saw when they described those distant sprays of light as a ‘milky circle.’ In 1610, Galileo used a telescope he’d built to confirm that the milky light was coming from countless individual stars. But out here off the Atlantic coast of Brazil, our scientific knowledge does nothing to dim the romance of a brilliant night sky.

The Milky Way is the galaxy that contains our Solar System. The descriptive “milky” is derived from the appearance from Earth of the galaxy – a band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. The term “Milky Way” is a translation of the Latin via lactea, from the Greek γαλαξίας κύκλος. From Earth, the Milky Way appears as a band because its disk-shaped structure is viewed from within. Galileo Galilei first resolved the band of light into individual stars with his telescope in 1610. Until the early 1920s, most astronomers thought that the Milky Way contained all the stars in the Universe. Following the 1920 Great Debate between the astronomers Harlow Shapley and Heber Curtis, observations by Edwin Hubble showed that the Milky Way is just one of many galaxies.
Age: 13.20 billion years
Number of stars: 400 billion
Apparent mass: 1.25 trillion solar-mass
Galactic group: Local Group
Constellation: Sagittarius