Jupiter’s moons right now
The four moons Galileo found, lined up beside the planet as you see them from Earth. Wind the site clock at the bottom forward to tonight, then go outside and check my work.
From Earth
East is on the left, as in upright binoculars from the northern hemisphere.
Distances and Jupiter’s disc are to scale. The moons are drawn larger than life so you can see them.
- Io
- Doing the sums
- Europa
- Doing the sums
- Ganymede
- Doing the sums
- Callisto
- Doing the sums
Distances and Jupiter’s disc are to scale. The view allows for the time light takes to reach us. How to find the moons with binoculars
From above
The same moment seen from over Jupiter’s north pole. Drag sideways to move time.
Hear the rhythm
Sound is off until you turn it on. Then each moon sounds a note every time it completes a lap, and the site clock sets the tempo. At a day a second, for each note from Ganymede you hear two from Europa and four from Io. Callisto keeps its own time. I rather admire that.
- Io
- 880 Hz, one note every 1.77 days
- Europa
- 438 Hz, one note every 3.55 days
- Ganymede
- 218 Hz, one note every 7.15 days
- Callisto
- 93 Hz, one note every 16.69 days
Io’s note is set to 880 Hz and the others are lower in proportion to their orbital periods from NASA’s fact sheet. Because the periods are close to, but not exactly, 1 to 2 to 4, Europa and Ganymede sound almost one and two octaves below Io. The pitches are my way of hearing the periods. The moons themselves make no sound.