Jupiter

Best time to observe: see chart

To locate:

Jupiter takes 12 years to complete its orbit about the Sun, thus it moves through the 12 zodiac constellations at the rate of one per year. You'll need to check the chart for when and where Jupiter will be visible.

Jupiter is the largest of the planets, and also very bright -- 2-1/2 times as bright as Sirius, the brightest star in the night sky. If you know when and where to look, Jupiter will be the brightest object around.

What to notice:

In the telescope, notice that Jupiter's disk is not round, but rather squashed and wider at the equator. This is because Jupiter is spinning so fast -- its day is only 10 hours long! On the disk itself, look for the white zones and dark belts. These bands are lined up east-west, and also the result of Jupiter's fast spin. Sometimes you can see storms, or irregularities, in the belts. If you see a pale reddish spot in the southern hemisphere, you've located the "Great Red Spot". This is a gigantic hurricane, about the size of 3 Earths. It's been observed for 300 years, so is at least that old. If you can see any detail in the bands, and are very patient, you can watch that detail move across Jupiter's disk as it rotates. It will take about 5 hours for an object to cross the disk.

The four largest moons of Jupiter are almost always visible. They'll look like tiny stars roughly lined up with Jupiter's equator. We call these the Galilean moons, because Galileo was the first to observe them. His discovery of these moons going around Jupiter helped convince people that the Earth was not really the center of the universe (although Galileo was punished for this idea). By the way, your telescope is about 2 times bigger than the one Galileo used, so you'll have a much better view than he did! The moons move quite fast, and you'll be able to see them change position during the evening. If you see fewer than 4 moons, the missing bodies are either traveling in front of, or behind, the planet. Sometimes you can see the shadow of one crossing the disk.

When all 4 moons are present, the closest to the planet is Io, bright with a slightly yellowish-orange tinge. Next comes Europa, pure white but dimmer than Io. Third is Ganymede, the brightest of all. Farthest from the planet (generally) is Callisto, the darkest.

What you are looking at:

Jupiter is a giant gas planet, made mostly of hydrogen and helium (the building blocks of the universe). Although it doesn't have any surface, the interior may be under enough pressure to have squeezed the hydrogen into a liquid, and there may be a small rocky core at the center. Most of what we see, of course, are the bright white clouds of frozen ammonia in the upper atmosphere. Places on the disk where these clouds are thin or absent shows us the lower, brownish belts of darker water and sulfur.

Sketch Jupiter and its moons.   Note the date and time.

When and Where to Look for Jupiter

Approximate position of Jupiter in the early evening hours:


     When         Where to look   
    Spring 1996   early AM only   
    Summer 1996       east        
      Fall 1996       west        
    Winter 1997    not visible    
    Spring 1997   early AM only   
    Summer 1997       east        
      Fall 1997       west        
    Winter 1998    not visible    
    Spring 1998   early AM only   
    Summer 1998   early AM only   
      Fall 1998       east        
    Winter 1999       west        
    Spring 1999    not visible    
    Summer 1999   early AM only   
      Fall 1999       east        
    Winter 2000       west        
    Spring 2000    not visible    
    Summer 2000   early AM only   
      Fall 2000       east


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