How to Find the Planets

The easiest way to locate all the planets is to follow Sky & Telescope's directions. Go to This Week's Sky at a Glance, and scroll down to This Week's Planet Roundup.

Mercury, Venus, Mars, Jupiter and Saturn are bright and easy to spot even from the city. Uranus and Neptune require a telescope and a finder chart. Pluto is still listed for old times' sake and is a challenge to find. You'll need a big scope, dark sky, and detailed star chart.

How to Identify Jupiter's Moons

If you have a telescope or binoculars that let you see Jupiter's moons, then the Jupiter's Moons JavaScript Utility from Sky & Telescope will help. It allows you to identify the four brightest moons at any given time. Adjust the time using your UT offset to determine the local time. The tool automatically retrieves the UT offset from your computer, but you may want to verify that it is correct.

You can confirm for yourself that the moons are constantly changing position. Click on one of the buttons repeatedly, e.g., "+1 hour," to simulate this.

Name That Moon

Photo courtesy of NASA and the NSSDC

Jupiter has 63 moons. The NASA web site has a list of the names.

The moons were named after the Roman god Jupiter's lovers, children and godchildren. Click on a name to see the lover or descendant's relationship to Jupiter, or go directly to the USGS Astrogeology site.

Notice that from the 50th moon on, the moons have catalog numbers. Those moons will eventually have proper names. Apparently Jupiter had no shortage of lovers.

References:

Naming convention explained

Poor Simon Marius

Who was Simon Marius? He was a German astronomer who claimed to have discovered Jupiter's four moons a few days before Galileo did. But he didn't publish his findings till 1614. Galileo published his in 1610, the same year he discovered the moons.

So instead of being famous for discovering Jupiter's first four moons, Marius is merely a footnote in history as the man who gave the moons their names -- Io, Europa, Ganymede and Callisto, named after lovers of Jupiter.

This is a portrait of Simon Marius. He sure looks mad, doesn't he?



References:

Galilean Moons
Simon Marius
Marius portrait

Jupiter Moon Dance

The year was 1610. Galileo, working from his home in Padua, Italy, pointed his homemade spyglass at Jupiter. Night after night, he noticed a line of four stars flanking Jupiter. These stars constantly changed position but never strayed far from the planet.

Galileo had discovered that Jupiter, like the Earth, had moons. The widespread belief that everything revolved around the Earth had just been proven wrong.

In this document, you can see the sketches Galileo drew of Jupiter and its moons as observed through his telescope.

Image courtesy of NASA
Today the four moons discovered by Galileo are known as the Galilean moons. In order of distance from Jupiter, they are Io, Europa, Ganymede and Callisto.

Here is a typical view of Jupiter and its moons, similar to what Galileo would have seen. At the time this photo was taken, Io was hiding behind the planet.

Photo courtesy of NASA/JPL/Malin Space Science Systems
References:

Galileo document
The Discovery of the Galilean Satellites
Wikipedia

Jupiter: The Gas Giant

If you look outside tonight, the brightest object you'll see in the southeast sky is Jupiter. If you live in the city, it may be the only thing visible in that area of the sky; you can't miss it. At magnitude -2.7, it's the third brightest object in the night sky next to the moon and Venus (Venus is not currently visible) and will be up for most of the night.

Jupiter is one of the gas giants, composed primarily of hydrogen. It takes less than 10 hours for it to rotate on its axis. The most prominent feature on the planet is the Great Red Spot (GRS), visible in telescopes. You'll see the GRS in the photo below.

Photo courtesy of NASA and the NSSDC
Related Posts:

Jupiter Moon Dance
How to Identify Jupiter's Moons
Name That Moon
Poor Simon Marius

References:
Wikipedia
Hubble Telescope photos