This week Hal talks about Ganymede, the largest moon in our solar system.
One of the brightest objects in the night sky for southern Colorado and northern New Mexico listeners right now is the amazing planet Jupiter. Shining brilliantly in the southern sky, Jupiter is so big it could hold 1000 Earths inside it. But there are other fairly big things out by Jupiter, and the biggest of all is Ganymede, the largest of the at least 67 known moons of Jupiter.
When it comes to moons, nothing in the solar system tops Ganymede. At almost 3300 miles across, Ganymede is not only the biggest moon in the solar system, it’s actually bigger than the planet Mercury. At, it’s three quarters as big as the planet Mars. If Ganymede was orbiting the Sun, it would be classified as a planet. But like a lot of things near Jupiter, the massive gravity of that massive planet keeps Jupiter and its nearly 6 dozen fellow moons close to home, astronomically speaking.
Ganymede is one of the four brightest moons orbiting Jupiter, commonly referred to as the Galilean moons. Galileo, during an eventful week in January 1610, spotted these bright points of light, all in a line, around Jupiter. By observing over a few days, Galileo was able to deduce that these moons were orbiting Jupiter itself. This was a dangerous idea when the official theology of the day had the Earth at the center of the universe, with everything orbiting it.
In an effort to give himself a little political cover, Galileo initially named these moons in honor of his patron and that rich man’s three brothers, but those names didn’t stick.
Ganymede is a fascinating place. There is some evidence of salt water deep under the surface, and traces of an oxygen atmosphere, though it’s far too thin to support life, at least as we know it on Earth.
If you’d like to take a closer look at Ganymede, or any of the other wonderful and amazing things in the sky, please visit KRCC.org or CSASTRO.org for a link to information on our monthly meetings and our free public star parties!
This is Hal Bidlack for the Colorado Springs Astronomical Society, telling you to keep looking up, Southern Colorado!