An eerie blue aurora floats above Jupiter in a newly released ultraviolet (UV) Hubble Space Telescope image, while three Galilean moons dance through the excitement.

The aurora is a curtain of light created by high-energy electrons racing along the planet's magnetic field into the upper atmosphere. The electrons excite atmospheric gases, causing them to glow.

The image shows the main oval of the aurora, which is centered on the magnetic north pole of the planet, plus more diffuse emissions inside the polar cap.

[inset]

In 1610, Galileo Galilei aimed a crude device with glass lenses mounted in a pipe organ toward Jupiter. Observing with the instrument -- it wasn't even called a telescope yet -- he saw three points of light around the planet and assumed they were distant stars.

As Galileo continued watching the "stars" each night, he noticed that they moved, appearing sometimes on one side of the planet, sometimes on the other. And the number of them changed. Soon, Galileo realized he was seeing four moons orbiting Jupiter. The names were given later.

In contrast to Galileo's challenging circumstances, the Hubble telescope sits above all the blurring effects of Earth's atmosphere and packs a lens that's nearly 8 feet (2.4 meters) in diameter.