JupiterMoons is your essential guide to observing the king of planets whenever Jupiter reigns over the night sky.

Sky & Telescope’s app helps you locate Jupiter’s four largest moons and time transits of the Great Red Spot with an easy-to-use interface. (The moons’ orbits are shown to scale with respect to Jupiter.) Plus, learn more about what makes these fascinating solar system denizens tick.

Observe Jupiter
• Locate Io, Europa, Ganymede, and Callisto at the specified date and time — unlike in Galileo’s day, they’re clearly labeled.
• Zoom in by tapping on the screen to better watch accurately timed Great Red Spot crossings and moon transits and eclipses. Or zoom out for a full view of the moons’ orbits.

Take Command
• Use the time controls to step through the seconds or hours, or speed through days or even years to see where the moons will be down the line.
• Customize your view to match what you see through your telescope.

Focus on the Details
• Click on any item in JupiterMoons’ complete events calendar to see the action. The calendar lists all the Jupiter-related happenings for the day: moon eclipses and transits, Great Red Spot transits, and moon-shadow transits.
• Learn more about Jupiter and its ice-and-fire moons with our encyclopedic descriptions, accompanied by spectacular images.

Please note: this application is designed to work in landscape orientation only so that you may view Jupiter, the Great Red Spot, and the Galilean satellites at their best.

What's New

Version 1.1

- Update to Great Red Spot longitude calculation
- Minor bug fix in the "What's happening with Jupiter” events list
- Removed cross hairs around Jupiter
- Updated general design

Ratings and Reviews

NOT for iPhone X!


I love this app, but I can’t use it now that I have an iPhone X. Until they update this don’t try to use this with an iPhone X — you can’t get back out of it.

useful and easy to use

Anthony in SF

This is a simple app that does one thing well: it shows and tells you when Jupiter's four Galilean moons and their shadows will be moving across Jupiter's face, when the moons will be passing behind Jupiter or through Jupiter's shadow, and when the Great Red Spot will be in the middle of Jupiter as seen from Earth, and thus most easily visible through a telescope.

I've been using the tables in Sky and Telescope Magazine to plan when to see Galilean moon transits, but this app makes it much easier and quicker -- you don't have to scan through a long table of fine print and mentally translate from Universal Time to your local time zone. It's all right on the screen with a clear diagram of what everything will look like through your telescope, and you can adjust the display to show an inverted or mirror image, to match the view through your instrument.

The supplemental information and images of Jupiter and the moons are well chosen and helpful, but the main screen is the reason to get this app.

As other reviewers have said, it would be nice to be able to set parameters for alerts, e.g. a shadow transit or occultation between 7 pm and 11 pm local time. Another quibble: this app only displays in landscape mode, which makes sense to get the widest diagram of Jupiter and the moons, but I would like to be able to shift into portrait mode because that's how I hold my ipad when I'm at the telescope.

Very thin application

PD Ferguson

This app is disappointing in how little it does. Besides the main display of Jupiter and its four visible moons' positions, it has very brief descriptions and a few photos of the planet and the four moons. It is far from a complete reference on Jupiter. For example, it mentions the fact that Jupiter has more than 60 moons, but contains no other information about them.

Compared to other full featured astronomy apps like Star Walk, Safari Pro, or Luminos, each of which costs only a few dollars more, this app delivers very little for the money.


Sky & Telescope Media, LLC
41.8 MB
Requires iOS 8.0 or later. Compatible with iPhone, iPad, and iPod touch.
Age Rating
Rated 4+
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  • Family Sharing

    With Family Sharing set up, up to six family members can use this app.

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