Jupiter is a gas giant planet consisting mostly of hydrogen and helium. Astronomers have discovered more than 60 moons orbiting Jupiter. In 1610 Italian astronomer Galileo discovered the four largest moons, although he saw them only as "stars." Today we know the large moons as volcanic Io, icy Europa, and cratered Ganymede and Callisto.

Have you heard of the Great Red Spot? This storm can have winds twice as fast as those in the strongest hurricanes on Earth. It is 2 to 3 times the size of Earth and has lasted for centuries.

Captions:
Inside the Observatory
During some evening stargazing events here, you can view Jupiter, its cloud bands and the Great Red Spot, and several of its moons. Over the course of just an hour, you can watch the moons change position and sometimes move in front of or behind Jupiter.

These images of Jupiter and two of its moons were taken through the Public Observatory's 4-inch finderscope over one hour on January 28, 2012.

This picture from 2007 combines a Hubble Space Telescope grayscale image of Jupiter and a false-color image from the Chandra X-ray Observatory. The Chandra image reveals intense auras (purple).
X-ray: NASA/CXC/SwRI/R. Gladstone et al.
Optical: NASA/ESA/Hubble Heritage (AURA/STScl)

As the New Horizons
spacecraft flew past Jupiter in 2007, it captured these images of Jupiter's largest moons (left to right): Io, Europa, Ganymede, and Callisto.
NASA/Johns Hopkins University
Applied Physics Laboratory/Southwest Research Institute

Viewing Our Solar System:
Juno
In 2011 NASA launched the unmanned solar-powered spacecraft Juno. Its goal is to explore Jupiter's neighborhood and colorful clouds. Juno will help scientists understand how a gas giant forms and changes. It may even answer questions about Jupiter's structure, whether the planet has a solid core, and how much water or oxygen it has. Juno should arrive at Jupiter in July 2016 and operate for a year.

Main image caption:
←An artist's concept of the Juno spacecraft arriving at Jupiter.
NASA/JPL

How to Learn More:
http://solarsystem.nasa.gov
http://missionjuno.swri.edu

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