In our skies: Jupiter’s moons lined up
One of the great resources we enjoy by living in this part of the country is our dark sky. Throughout the winter, those dark skies will become clear and provide us an unparalleled opportunity to view the many wonders of our solar system and the universe. A lot can be seen with the naked eye, even more with a good pair of binoculars. Fantastic viewing is available with a telescope.
If you haven’t yet gained an appreciation for our wonderful skies, try looking at the sky from inside the city of Tucson
Jupiter has about 63 known moons. The four largest and the ones you can see through a good pair of binoculars are Io, Europa, Ganymede, and Callisto. These were the first four of Jupiter’s moons to be discovered by Galileo in 1610. Today they are referred to as the Galilean moons.
Io is covered with volcanoes and is the most volcanically active body in our solar system. Its surface resembles a pizza.
Europa is covered with water ice and scientists believe that there may be large lakes or even oceans of slush under the surface.
Ganymede is the largest moon in the entire Solar System. It is larger than the planet Mercury and is the only moon we know of that has its own internally generated magnetic field.
Callisto’s surface is very heavily cratered like our moon, but we believe they date from the early history of the Solar System. The very few small craters on Callisto would indicate a small degree of current bombardment activity.
When you look at Jupiter through good binoculars you will see up to four moons alongside it. As they orbit, one or more could be behind it or in front of it and invisible in the bright light reflecting from Jupiter. They also orbit with different periods. Io takes 1.8 days to circle Jupiter; Europa, 3.6 days; Ganymede, 7.2 days; and Callisto, 16.7 days. Therefore, without a table to refer to, it is very difficult to determine which moon is which.
Jupiter is high in the sky early in the evening so get out and have a look.
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