They are not technically planets as they do not orbit the Sun, but they’re round, world-like objects. Each of these satellites is a planet in its own right. These are the Galilean satellites: The Moon-sized rocky planets Io and Europa, and Mercury-sized ice-balls Ganymede and Callisto. Jupiter has 80 known natural satellites (‘moons’), but only four are big enough to be seen by amateur observers. Jupiter goes between about 4.2 au and 6.2 au away from the Earth, depending upon the relative position of the two planets as they circle the Sun. Using this vast distance as a yardstick, Jupiter’s distance from the Sun is 5.2 au. More useful when thinking about the solar system is to set the distance between the Earth and the Sun equal to 1 au (Astronomical Unit). This distance is so huge that it’s basically worthless if you want to get an idea of the scale of the solar system. Jupiter orbits the Sun every 11 years, 10 months, and 10 days, at a distance of 778 million kilometers. Different features may be seen by waiting a short time, and you may notice the rotation when observing at high power for even as little as 15 minutes. So it takes roughly 5 hours for a feature on one edge of Jupiter to rotate across to the other edge, or just 2.5 hours to go from the edge to the middle of the planet. It rotates on its axis once every 9 hours, 55 minutes, and 30 seconds. These changes can occur over timescales of months, years, or decades. Storms can grow, merge, and change color. The overall structure of cloud belts remains the same, but the belts can change color or width. Jupiter changes its appearance over time. When we look at Jupiter with a telescope, the part we see is mostly ice-crystal clouds made of ammonia (white) and ammonium hydrosulfide (brown) ices. But there is no surface–Jupiter’s layers sort of smoothly blend into one another. At the center is a massive, hot, icy core. It’s called a “gas” giant because those are gases on Earth, but gas giants like Jupiter and Saturn are mostly made of extremely hot, extremely high-pressure liquid hydrogen with a cooler hydrogen-helium atmosphere. Jupiter is 139,900 km across, or 11 times wider than the Earth and 318 times more massive. Jupiter is a gas giant-a planet made mostly of hydrogen and helium. If you don’t know where Jupiter is, and you’d like a little more guidance on what to look for on the planet, read on. Jupiter also has two faint dark stripes, or “cloud bands”, which run parallel to the equator. Look for the moons, which appear as four stars, kind of in a line with Jupiter’s equatorial plane. It will still look pretty small, even at higher magnification. You may then increase the magnification with a shorter focal length eyepiece. It will appear as a fairly small, bright dot. Use a low magnification, long focal length eyepiece to find and center the object. If you already know where Jupiter is, or you know how to find it with an app, go ahead and just point your telescope at it. The giant planet Jupiter is one of the easiest planets to find and observe in the solar system. Do check because it's a lot easier if you can check orbital alignment of Galilean moons as seen from Earth directly on the field, as you're doing your observations.In this article, we’ll go over how to find Jupiter with the naked eye, as well as how to get the most out of seeing Jupiter using a telescope. I think even this one is available as an app for smartphones for free, but last time I tried to install it, it didn't work for me. But there are many such tools online or downloadable for both computers and smartphones. Note that this mentioned tool does offer settings to switch between orrery and realistic model and large and realistic sizes of displayed celestial bodies. I use the old neck twisting and turning technique, but photo editing tools or even rotatable screens will do just as well, if not better. Note that it might take a bit of rotation for you image to align perfectly. Then compare with the photograph that you took. Then double-click on Jupiter, then its Orbit button, then click on link As seen from Earth below, then click Go back button and use mouse wheel to zoom out so all four Galilean moons display. What you do in this particular tool is click on the calendar bar below and enter date and time of your observation (if you forgot that, there's a good chance your photograph has a time stamp, either of the file or in its EXIF data). There are some quite fancy ones online, for example this Solar System Scope: Use an orrery that will let you specify a specific epoch and vantage point.
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