Yesterday I wrote how Jupiter and Venus are close to each other right now in the morning sky. It is an interesting phenomenon that can be seen only during few days. Sad but true, it has been very lousy weather for astronomers here in Finland, and therefore I have not been able to observe Jupiter and Venus. Anyhow, let us now continue a little bit more with Jupiter.

The giant planet Jupiter has several moons orbiting it, and some of them can be seen by the naked eye. Is it really so? Yes, it is possible but not very easy because of Jupiter’s glare effect. Jupiter is very bright and therefore the little moons hard to observe. In order to observe them by the naked eye, we need to find a way to deal with the glare effect of Jupiter.

The four biggest moons of Jupiter are Io (brightness is 5.0 magnitudes), Europa (5.3 mag.), Ganymedes (5.3 mag.) and Callisto (5.6 mag.). Jupiter itself is 600 times brighter than its moons, so it is not a wonder we cannot see them moon easily.

Io and Europa are located so close to the planet that we cannot see them by the naked eye. Fortunately the most distant moons, Callisto and Ganymedes are possible to observe by the naked eye, but only in good conditions. Such a condition exists when the observation area has no artificial lights around, our Moon is not shining, the sky is clear, Jupiter is located high in the sky and the moons of Jupiter are located as far from Jupiter as possible (this phenomenon is called elongation). There are several charts and computer software in the market with which you can estimate the best possible elongation to observe Jupiter’s moons. This timing depends on your location, but for example in Helsinki (where I am located) Jupiter moons can be observed in February 18th.

It is not easy to observe Ganymedes and Callisto by the naked eye, but several astronomers around the world have reported successful observations. You can try to find them by setting an object over Jupiter in order to decrease the glare effect of Jupiter. Try observing the moon from behind a small tree or electricity wire so that the object covers Jupiter and decreases its glare effect. If you are lucky, you can see one or two small spots, the moons, close to Jupiter. Remember this is a difficult task, so you might have to try few or even dozens of times. Wait for optimum conditions, find out when elongation happens and give it a try.

Where is Jupiter? The location of Jupiter in the sky depends on your location and time. You can use the picture of my previous post to get an idea in which direction Jupiter is in winter when observed from northern latitudes.

Image source.