Astronomy: Prime time to observe Jupiter


You can observe Jupiter 1,000 times and never see the same planet twice. It is up in the early evening now, and is certainly the best reason to own a telescope.

Look south just after it gets good and dark, which won’t be until 10 p.m. because of the accursed daylight saving time. Jupiter will be the brightest point of light in the constellation Virgo.

At 89,000 miles in diameter, this giant ball of mostly hydrogen is the largest planet in our solar system. If Jupiter were the size of a soccer ball, Earth would be about the diameter of a dime. Thus, Jupiter looks large in a small telescope, even at its current distance of 440 million miles.

What makes Jupiter so beautiful is its 600-mile thick layer of clouds. Underneath those clouds is a ball of mostly hydrogen and helium in liquid form. Thus, the common way of referring to Jupiter as a gas-giant planet is incorrect. Jupiter is a liquid giant. Calling it a “gas giant” because of its layer of gaseous atmosphere is akin to calling Earth a gas midget because of its thin layer of air.

The planet spins once every 9.9 hours on its axis, making it the fastest rotator in our solar system. A stationary object floating in the clouds at Jupiter’s equator would be traveling at about 28,000 miles per hour.

The planet’s rapid rotation stretches its clouds into enormous bands that span the entire disk of the planet. Jupiter’s stripes, which are parallel to its equator, are caused by an odd effect that is typical of such giant, fluid balls.

Jupiter’s rotation is not constant over its entire sphere. The rotation of Jupiter at its poles takes about 5 minutes longer than the rotation at the equator. The 9.9 hours is actually an average rotation for the entire planet. That effect is spread out over the entire planet. Essentially, what you are seeing when you see the bands are regions of varying rotation.

The banding effect is made even more pronounced by the heat generated by such a massive ball of liquid.

In fact, the shape and size of the cloud bands are constantly changing. Jupiter’s enormous gravity exerts tremendous pressure on its innards. The pressure at the core is 30 million times higher than we find on Earth. As a result, the interior of the planet is much hotter than the outer cloud layers — 55,000 degrees compared to 200 degrees below zero.

Jupiter actually generates more energy of its own than it gets from the sun.

Great heat waves bubble up from the core, twisting and turning the cloud belts. The bright bands of clouds, usually white or yellow and composed mostly of ammonia crystals, are the higher, colder clouds being driven up by the warm gases. The dark belts, usually red or brown, are lower clouds descending as they lose their heat.

Those bands seem to change from day to day, with swirls and undulations and little hook-shaped protuberances called festoons.

High in the upper cloud layers are storm systems, cyclones that dwarf those on Earth. In fact, these mostly white ovals can be as large as our planet. They can have winds of over 250 miles per hour and can last for a year or two. But they often appear and disappear from observing session to observing session.

The granddaddy of Jupiter’s storms is the Great Red Spot, a normally rust-colored oval 25,000 miles wide. It’s been around for at least 300 years – since the first telescopes were trained at the planet. Some astronomers estimate its age at 30,000 years or older. That’s one heck of a hurricane.

The spot changes color from red to a pale pink from year to year as the storm sucks up different colored elements from deeper in Jupiter’s atmosphere.

At high magnification, your scope may reveal the Spot’s complex structure – material swirling in and around the storm.

But you aren’t stuck just observing the planet. At low magnification, you’ll see Jupiter’s four brightest moons. They are wonderful to watch as they slowly change their positions, performing their cosmic dance around Jupiter.

If you’re really lucky, you might get a chance to see one of nature’s most spectacular events. When a moon passes in front of Jupiter, its dark shadow on the cloud tops looks like a tiny black hole boring into the face of the planet.

Jupiter will be visible for a couple of months more before it passes below the horizon, but now is the prime time to observe it.

Poetry at Perkins

On Saturday, June 3, at 8 p.m., Perkins Observatory will hold its annual “Poetry at Perkins celebration. The event, cosponsored by Full Crescent Press and the Ohio Poetry Association, will feature Central-Ohio poets reading their favorite astronomical poetry.

After the poetry, we’ll be observing the night sky with telescopes, including the observatory’s own Schottland Reflecting Telescope, weather permitting.

Tours of the observatory, including a ghost story, will also be available. Tickets are $10 in advance and can be obtained by calling 740-363-1257. Seating is limited, so advance tickets are recommended.

Tom Burns


Tom Burns is director of the Perkins Observatory in Delaware.

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