Keeping an eye on Jupiter and its many moons

Hi Sky Guys and Gals, Time to look at the sky again, as we do each month.

I have told you before that there are many things we can see in the sky with our naked eyes, but even more with binoculars. We have discussed good binoculars for astronomy, and how to use them.

This month I want to talk about the planet Jupiter, or in particular, some of its moons. Jupiter, first, can be seen in the sky after sunset, in the southwest. But look soon because by this month’s end, it will be lower, and in the southwest, and thus not as good to view because it will be through more atmosphere. So look now. Now – the moons. We have one moon. Jupiter has many, numbering in the 60s. There are four larger ones nearer to Jupiter, known as the Galilean moons. These can be seen as “tiny diamonds” circling around Jupiter, and are visible in binoculars.

The four are named: Io, Europa, Ganymede, and Callisto. They circle Jupiter, and as long as Jupiter is visible, you can see two to four at any given time. They can disappear as they pass in front of, or behind the planet. To find which ones are visible on any given night there is a diagram published in each issue of Astronomy, Sky & Telescope and Sky News.

Let’s look at these four moons:

1.Io is “close” to Jupiter and is very volcanically active. It recycles its entire surface every 100 years.

2.Europa may be the most interesting. It is covered by an icy surface, and there may be a deep ocean underneath, with the possibility that life forms may exist in the ocean. 3.Ganymede – its claim to fame is that it is the largest moon in the solar system. It is actually larger than the planet Mercury.

4.Callisto is the most distant of the four from its parent planet – Jupiter. It is a rocky rough surfaced moon.

Be sure to find a clear night, find Jupiter, and look at these tiny gems. Finally if you watch them each night, you will see how they have changed position.

Now - what is in the sky this month?

As always, first the night sky. There is one special event involving Jupiter you can try. On July 28, the planet is directly below the crescent moon. It is a good opportunity to see a planet in the daytime, which is ordinarily very hard to do. Look before sunset for the moon, then go below and find Jupiter. Binoculars can help, but you must be careful not too look at the sun in your binos. You can blind yourself.

Saturn is also in the night sky. One hour after sunset, we find Saturn high in the south-southeast. By the end of twilight, it’s high in the south. Mercury is in the sky this month. Look in the west-northwest late in the first week of July. It is not a good month to view because it never comes much above the horizon although it is up most of the month.

The morning sky is all Venus – big, bright, beautiful – rising two and a half hours before sunrise. Try and follow it after the sun rises. It will be very much dimmer.

Don’t forget to look for the asterism “The Teapot” low in the south once it gets good and dark.

That’s it again. See you in a month.