There’s a bright shiner lighting up the Butler heavens these warm late spring evenings.

It’s Jupiter, the big guy of the solar system. Without a doubt, it’s by far the largest planet, overwhelming any other star or planet in brightness.

Only the moon is brighter, but its absence from the evening sky this week makes Jupiter the brightness king.

The reason it’s so bright is twofold.

First, Earth and Jupiter are still relatively close to each other right now, separated by just under 437 million miles. Late last month they were separated by under 420 million miles, their closest encounter in 2017, in what astronomers call opposition.

The second reason Jupiter is extremely dazzling is that Jupiter is one monster of a planet, 88,000 miles in diameter, more than ten times the diameter of Earth. In fact, if Jupiter were a hollow sphere you easily fit more than 1,300 Earths inside it.

With a small telescope or even a decent pair of binoculars you can resolve the disk of the planet and maybe even see some of its cloud bands, especially two dark ones on both sides of the equator.

What easily catches your eye, though, are up to four little starlike objects that accompany Jupiter. They’re either to the left or right of Jupiter and they’re constantly on the move from night to night.

These are Jupiter’s four brightest and biggest moons that obediently orbit the planet in periods of two to 17 days, all within 1.2 million miles of the Jovian planet.

The moons Io, Europa, Ganymede, and Callisto are constantly changing position relative to Jupiter and each other, and every night you see them they’re arranged differently. Some nights you can’t see all four because one or more moons may be temporarily hiding behind Jupiter or passing in front of it, camouflaged by Jupiter’s brightly sun lit clouds.

What I think is really cool is when one of the moons is really close to the edge of Jupiter, and over several hours you can see it slip in back of or in front of the planet.

If you have a medium to large telescope you can sometimes see the shadow of the moon that happens to be crossing in front of Jupiter. It’s just a tiny black dot, and it can be really tricky to see.

One of the tricks of the trade when using a telescope is to observe in continual stretches of at least 10 minutes to get used to light levels coming into your eyepiece. Quick glances just don’t cut it most of the time, especially with the planets.

There are many good sources on the Internet that keep you up-to-date with the arrangement of the moons from night to night. One I use is from “Shallow Skies” at www.shallowsky.com/jupiter/

One of the better apps to keep tabs on Jupiter’s moons is simply called JupiterMoons from Sky and Telescope Media.

I have a diagram of the positions of the moons around Jupiter for this coming week to get you started.

These four brightest moons of Jupiter are referred to as the Galilean moons. They were named after the great astronomer Galileo, who saw them for the first time in 1610 in his crude telescope, and concluded from their night to night position changes that they were orbiting Jupiter.

He used these observations to help plead his case that the Earth and other planets like Jupiter were actually orbiting around the sun instead of the Earth-centered universe as was widely believed.

Unfortunately for him he wasn’t able to persuade the Catholic Church or the government of his theory, and was put under house arrest.

The Galilean moons Io and Europa are two of the most interesting bodies in our solar system.

Io, Jupiter’s closest moon, has constant volcanic activity because of the strong gravitational tides caused by Jupiter. The 2,200-mile-wide moon, about as big as Earth’s moon, is under constant torture as it’s constantly pulled and stretched, which generates interior heat and a molten core resulting in hundreds of volcanic eruptions. Because of all those eruptions Io has an atmosphere made of sulfuric dioxide that collapses and freezes when Jupiter blocks the little moon from the light and heat of our sun.

Europa, Jupiter’s smallest Galilean moon at less than 2000 miles in diameter, is one of the leading candidates for life beyond Earth in our solar system. Its surface is the smoothest in our solar system as it’s completely covered by a fractured sheet of ice.

Because of the same strong tidal forces it may be warm enough in Europa’s interior that underneath its icy surface is possibly a slushy ocean of liquid water.

In fact, the Hubble space telescope has imaged what may be water vapor plumes erupting off the surface of Europa, and where there’s liquid water there may be life as we know it.

What is not known for sure is how thick the ice on Europa is, but these plumes of water vapor may indicate that the ice isn’t all that thick.

There are plans in the works to send landing crafts to Europa to drill into the ice, and the less drilling they have to do the better. The observation increases the possibility that missions to Europa may be able to sample Europa’s ocean for life without having to drill through miles of ice.

Stay tuned and follow the dancing moons of Jupiter.

Make the stars your old friends

If you have any astronomical questions or want me to write about something you’re seeing in the night sky, drop me a line at mikewlynch@comcast.net.

Mike Lynch is an amateur astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis/St Paul and is author of the book, “Stars: a Month by Month Tour of the Constellations” published by Adventure Publications available at bookstores at http://www.adventurepublications.net