Caption: Galileo's drawings of Jupiter and Galilean moons (obtained from observations with early telescopes) published in the Sidereus Nuncius (1610, in English The Star Messenger).
Galileo discovered 3 of Galilean moons before about 1610 Jan07. The 4th one was discovered before 1610 Mar02 (Wikipedia: Galilean moons: Discovery).
The Galilean moons oscillated about Jupiter on approximately a single line. Obviously, they were natural satellites and, from a Copernican in which the Earth is planet, they were moons of Jupiter.
The page from the Sidereus Nuncius shows the Galilean moons at different periods, and thus reveals their oscillation around Jupiter.
Galileo named the new moons the Medician stars for his patrons, the Medici---but posterity disposed of that idea and called them after Galileo himself.
Credit/Permission:
Galileo Galilei (1564--1642)
1610
March
(uploaded to
Wikimedia Commons
by User:Chiswick Chap,
2013) /
Public domain.
Image link: Wikimedia Commons.
File: Jupiter moons file:
galilean_moons_galileo.html.