The planet Jupiter is back in the night sky and has something for every amateur astronomer to enjoy.
The rather dim constellations of fall are enlivened this year by the brilliant presence of the gas giant planet Jupiter in their midst. For the casual stargazer, it shines like a bright beacon in the otherwise rather dull autumn skies.
This sky map shows where to look to spot bright Jupiter in the eastern night sky. You can?t miss it, though ? just go out soon as it?s dark, face east, and look up.
Ordinary binoculars, particularly if steadied on a ledge or tripod, give you a chance to replicate one of Galileo?s great observations of four centuries ago: Even a 7x or 10x binocular will show Jupiter?s four brightest moons as tiny specks of light aligned with the planet?s equator, changing from night to night.
With even the smallest telescopes, this dance of Jupiter?s moons is revealed in great detail. A planetarium program will let you identify the four moons by name. [Photos of Jupiter and its moons.]
With a larger telescope (3 inches aperture or more) you can watch the shadows of the moons as they pass across the face of Jupiter, causing eclipses on the cloud tops beneath.
When the moons themselves pass in front of Jupiter, they often are lost in the brightness of Jupiter?s clouds, though Ganymede and Callisto are large enough and dark enough to show up as grey spots in front of the clouds in telescopes with at least 5 inches aperture.
Because Jupiter is a ?gas giant?? a planet made almost entirely of gas ? all we can ever see of it is the topmost levels of its dense cloudy atmosphere. Because of its large size and rapid rotation, its upper cloud surface has developed a complex and fairly stable appearance.
The rapid rotation, once every 10 hours or so, forces the clouds into strong horizontal bands known as belts (dark red and brown) and zones (light beige and cream). The widest and darkest belts can be seen in telescopes with apertures as small as 3 inches ?and magnifications as low as 50 power.
Clouds of Jupiter
Larger amateur telescopes reveal increasing amounts of detail in Jupiter?s clouds. This includes greater numbers of fine belts and detail within the belts. A 6- or 8-inch telescope can show more detail on Jupiter than can be viewed on any other planet in the solar system, making Jupiter by far the most rewarding planet for amateur study.
The details of Jupiter?s belts are mainly made up of ovals, whorls and streaks. As seen in a small telescope, these blend into each other to give the illusion of fairly smooth solid belts, but at moments of good ?seeing,? when the Earth?s atmosphere is stable, these resolve to show their true nature.
The most remarkable structure in Jupiter?s atmosphere is the Great Red Spot. This is a gigantic circular storm, three times the diameter of ?Earth, forced into an oval by the strong atmospheric currents surrounding it.
Despite being an atmospheric feature, it is amazingly stable, having been observed more or less continuously for almost as long as telescopes have existed, well over 200 years. It has changed in size, intensity, and color over the years, and drifted back and forth in longitude, but has retained its continuity throughout.
Perhaps its most remarkable feature is the distinctive color from which its name derives. Though sometimes pale white and other times brick red, it mostly shows a very distinctive pale salmon color. Under poor ?seeing? conditions, you can sometimes detect it only by its color, when no oval can be seen.
At present, the Great Red Spot is a difficult object to see in a small telescope.
To observe it, you first have to be looking at the correct side of the planet. Because of ?the ?planet?s rotation and fading at the edge, the spot is ?visible for only about three hours out of every 10. Even when well-placed, it is a low-contrast object, and requires a high-quality optical system and stable observing conditions.
Because Jupiter?s details are made up of nothing but clouds, they can change radically from year to year or even from month to month. This year, observers have been startled to discover that Jupiter, instead of having the two dark belts we?re used to seeing, has only one.
This year the south equatorial belt, in which the Great Red Spot is usually embedded, has faded to a pale white. The effect is such that the Great Red Spot appears on a background of white, as shown in this recent Jupiter photo by Australian amateur astronomer Anthony Wesley.
Skywatchers see Jupiter hits
Jupiter seems to be a magnet for comets, asteroids and meteors.
Comet Shoemaker-Levy 9 was observed crashing into Jupiter in 1994. Last year, ?Wesley imaged another apparent scar from an impact.
On June 3 of this year, Wesley in Australia and another amateur astronomer, Christopher Go, in the Philippines, independently recorded the impact of another meteor. Another fireball apparently struck the planet in August.
Many amateur astronomers today are monitoring Jupiter with webcams, so the chances of catching these events, once thought to be rare, are increasing.
So, even after two centuries of close examination, Jupiter is constantly yielding new surprises for astronomers. Take a look at it tonight.
- Photos - Rogue Asteroid Hits Jupiter
- Video - Fireball on Jupiter: Asteroid Hits Gas Giant
- New Fireball on Jupiter Spotted By Skywatchers
This article was provided to SPACE.com by Starry Night Education, the leader in space science curriculum solutions.
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Geoff Gaherty was Space.com's Night Sky columnist and in partnership with Starry Night software and a dedicated amateur astronomer who sought to share the wonders of the night sky with the world. Based in Canada, Geoff studied mathematics and physics at McGill University and earned a Ph.D. in anthropology from the University of Toronto, all while pursuing a passion for the night sky and serving as an astronomy communicator. He credited a partial solar eclipse observed in 1946 (at age 5) and his 1957 sighting of the Comet Arend-Roland as a teenager for sparking his interest in amateur astronomy. In 2008, Geoff won the Chant Medal from the Royal Astronomical Society of Canada, an award given to a Canadian amateur astronomer in recognition of their lifetime achievements. Sadly, Geoff passed away July 7, 2016 due to complications from a kidney transplant, but his legacy continues at Starry Night.