What you can — and can’t — see of Jupiter’s moons

Galileo’s four moons are easy. The other hundred-plus need some of the largest telescopes on Earth.

Published 2026-10-23

Jupiter has 115 known moons as of April 2026.^[4] Only a handful are within reach of a backyard telescope.

The Galilean four

Io, Europa, Ganymede and Callisto were discovered in 1610 by Galileo Galilei and Simon Marius with early telescopes.^[4] Today almost any telescope shows them as bright points that change position from night to night.

The irregular crowd

Most of Jupiter’s moons are small irregular satellites on distant, tilted, often retrograde orbits.^[4] Callirrhoe is one: only about 8.6 km across and some 24 million km from Jupiter.^[2][3]

How faint is faint?

Callirrhoe was found with a 0.9 m telescope, and most later irregular moons were found with 2.2–4 m telescopes and sensitive cameras.^[2][4] They are far beyond amateur equipment.

What to look for instead

With a small telescope, watch the Galilean moons cross in front of Jupiter and cast shadows on its clouds. Our telescope picker can help you choose a scope suited to planets.

Numbered citations link to the sources list on the Callirrhoe overview page.