Our line of sight to Jupiter also means that the moons can transit (or cross) the planet disappear or emerge from behind it (occultations) or even pass in front of one another! While the moons themselves are difficult to see while transiting Jupiter, their little round, black shadows are easy to see in a decent telescope. Because the moons seldom line up symmetrically, it's simple to compare what you are observing in your eyepiece with the app, and configure the flip buttons until it's the same. Some of the apps allow you to select the mode that matches your equipment. Unlike binoculars, most telescopes will invert or mirror image your view of Jupiter. For iOS users, the Jupiter Guide app, the Gas Giants app and the Sky & Tel app noted above all show a clear view of the arrangement of the planet and the moons, and offer a slider or buttons to alter the time. ![]() Your sky-charting app will have at least the four Galilean moons labeled, and perhaps some additional fainter ones. It usually takes only a short while to notice the moons shifting in position. Night mode turns the screen red to preserve your dark adaptation. The JupiterMoons app for iOS shows the correct arrangements of the moons and the planet at any date and time, and allows you to flip the view to match your telescope. Their differing orbital speeds produce different arrangements of the moons: close together, well separated, arranged symmetrically and sometimes all clumped to the left or right (east or west) side of Jupiter. Even modern-day binoculars are better than Galileo's little spyglass, so you can look for them yourself! Unlike the Earth's axis, which is tilted with respect to the solar system plane, Jupiter sits up straight, so the Galilean moons fall somewhere on a straight line that runs parallel to the planet's equator. Close-in Io moves faster than the outer ones, needing only 1.8 days to orbit Jupiter, while distant Callisto takes nearly 17 days. From closest to farthest from Jupiter, they are Io, Europa, Ganymede and Callisto. ![]() By observing the moons nightly over a period of weeks, he discovered that they were orbiting Jupiter - a controversial statement in his day!Īstronomers commonly refer to the big four as the Galilean moons. The four largest moons were first observed by Galileo Galilei in 1609 using a very modest telescope. ![]() Jupiter has more than 60 natural satellites, or moons - mainly, small objects that have been trapped by the massive planet's gravity. A separate page provides a list of upcoming GRS transits in local time, and another offers plenty of Jupiter facts and figures. It allows you to view the planet's current appearance and move forward and backward in time, in increments ranging from seconds to years. Sky and Telescope has a very good app for iOS called JupiterMoons (developed by the SkySafari app team). (Image credit: SkySafari App for iOS and Android)Īnother option is to choose an app that focuses exclusively on Jupiter. ![]() Late on Tuesday, March 15, 2016, the moons Io and Europa will cast their black shadows on the planet, and the Great Red Spot follows behind them. Most stargazing apps will show you an image of Jupiter, but to present the Great Red Spot correctly, they must take into account light-travel time to ensure accurate timing information. If you push the date forward on your app, it will show you that Jupiter becomes a morning object in late fall By July 2016, Jupiter will appear low in the western evening sky, soon becoming too close to the sun to be observable. Your favorite sky-charting app ( SkySafari 5, Star Walk 2, Sky Guide, Stellarium, Star Chart, Google Sky Map, etc.) will have no problem confirming this for you on your mobile device. In March 2016, Jupiter is sitting below the stars of Leo in the eastern evening sky. There's no better time to install some apps to help you locate it, track the motion of the four Galilean moons, find out when the Great Red Spot is visible and learn some Jovian science! Finding Jupiterĭespite Jupiter's great distance, the planet's size reflects a lot of sunlight, making it second only to Venus in brightness among the planets, and outshining every star in the night sky. That's nearly as large as Jupiter ever appears. In your binoculars or telescope, Jupiter will appear with a disk diameter of 44.5 arc seconds (about 2 percent of the full moon's diameter).
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