♃ Jupiter's Moons
Find out where Io, Europa, Ganymede and Callisto are relative to Jupiter right now: a diagram for the chosen date and time, a 7-day motion chart and a list of events for the next 2 days — transits, shadows on the disk, eclipses and occultations. Suitable for binoculars and telescopes; the calculation runs in your browser.

Jupiter's Moons by Date

Find out where Io, Europa, Ganymede and Callisto are relative to Jupiter right now: a diagram for the chosen date and time, a 7-day motion chart and a list of events for the next 2 days — transits, shadows on the disk, eclipses and occultations. Suitable for binoculars and telescopes; the calculation runs in your browser.

What You Can Observe

◉ Transit
A moon passes in front of Jupiter's disk. A dark moon against the bright disk is hard to spot, but its shadow is easy to see.
◼ Shadow on the disk
A black dot on Jupiter's clouds is the moon's shadow. Visible even in small telescopes.
🌑 Eclipse
The moon enters the planet's shadow and vanishes, then flares up again. It looks like a point of light being “switched off”.
● Occultation
The moon hides behind Jupiter's disk and, after a while, reappears from the opposite limb.

How to Use

  1. Choose the date and your local observation time
  2. The diagram shows where each moon is relative to Jupiter (east on the left, west on the right)
  3. The chart shows the moons' motion for the next 7 days: the sinusoids cross Jupiter's band during transits and occultations
  4. Below are the event times for the next 2 days; the ‹ and › buttons shift the date by one day

FAQ

Which moons of Jupiter can I see?
The four largest, the Galilean moons: Io, Europa, Ganymede and Callisto. They were discovered by Galileo in 1610. Even binoculars on a steady mount show them as four dots along the line of Jupiter's equator.
How do I read the diagram?
North is up, east is left, west is right, as in the sky. In a telescope the image may be inverted or mirrored, depending on the optics. Distances are given in Jupiter's equatorial radii.
What are a transit and a shadow on the disk?
A transit is the passage of the moon itself across Jupiter's disk. The shadow on the disk is a dark spot the moon casts on the planet's clouds. It is visible in a small telescope and often appears before or after the moon itself.
Why does a moon vanish near Jupiter?
There are two reasons: the moon goes behind the planet's disk (occultation) or enters Jupiter's shadow (eclipse). The second case is easy to watch: the moon “fades out” and “flares up” right next to the planet.
How accurate are the calculations?
A simplified low-accuracy method by Jean Meeus is used, with orbital corrections. The moon positions are good for visual observing, but event times may differ from precise ephemerides by a few minutes. For timing, use professional ephemerides.
Is my data sent to a server?
No. All calculations run in your browser.