Jupiter (left) and Saturn appear at dawn on May 9, 2021. Jupiter shines from Aquarius, with Saturn in neighboring Capricornus. (Bob King)
There's always a moment of excited anticipation when bringing the planet into focus again after a long hiatus. With no solid surface, Jupiter is all clouds and weather. Just as changing weather patterns alter Earth's external appearance from space, so too at the fifth planet. The Great Red Spot changes colors. New storms form and dissolve. Even prominent cloud belts can disappear and reappear.
When I pointed a 6-inch telescope at the planet on May 11, the planet's two most prominent
"stripes" immediately jumped out — the North and South Equatorial Belts (NEB and SEB). Both straddle either side of Jupiter's equator. The northern belt was dark and obvious, while its southern counterpart appeared paler and thinner.
This side of Jupiter, photographed on May 1, 2021, doesn't show the Great Red Spot. I labeled the most obvious belts and zones visible in a modest telescope. NTB = North Tropical Belt; NTrz = North Tropical Zone; NEB = North Equatorial Belt; EZ = Equatorial Zone; SEB= South Equatorial Belt and the STrZ = South Tropical Zone. Oval BA (a.k.a. Red Spot Jr.) as well as a half-dozen smaller ovals (storms) are also seen. (Anthony Wesley)
Jupiter displays a series of alternating dark belts separated by bright zones. Gas descends in the belts, where temperatures are warmer, and wells up in the chillier zones. The biggest zone is the Equatorial Zone (EZ). Normally white or pale yellow, this season much of it is veiled by a yellow-orange haze.
Zones appear pale because of upwelling cirrus-like clouds made of ammonia ice crystals. In the belts, as the air descends and warms, the bright ammonia ice evaporates, which allows us to gaze into the darker clouds below. Exactly what colors them is unknown, but their rusty hues may be due to compounds of carbon, sulfur and phosphorus that form at these lower, warmer altitudes.
The vertical black line equals zero wind speed. The jaggedly black line shows the strength and direction of winds in Jupiter's alternating belts and zones. (NASA)
Wind speed and direction varies with latitude at Jupiter. Near the poles it barely blows but increases to over 300 miles an hour (500 kph) within the prominent belts and zones on either side of the equator. The winds zig-zag from west to east and back again as you pass from one zone or belt to the next.
Jupiter looks oddly distorted because this photo was taken up close by NASA's Juno spacecraft in February 2019. Besides the Great Red Spot we also get a bird's-eye view of several stormy ovals. (NASA/JPL-Caltech/SwRI/MSSS; Processing: Kevin M. Gill)
The Great Red Spot (GRS) is a persistent, hurricane-like storm that has been observed since the mid-17th century, while the white ovals are smaller storms with shorter lifetimes. Through a small 4-inch to 6-inch telescope, ovals are really tough to see, but the orange-red GRS is visible at magnifications of 100x and higher. The best time to see it is when it faces us square-on during transits. To find transit times for your location, click here. You have about two hours centered on the transit time to see the Spot best. . For all its heft, the planet rotates rapidly, taking only about 9.9 hours to make a complete spin.
I took this photo of Jupiter and its four brightest moons by holding my cell phone up to the telescope eyepiece. (Bob King)
Jupiter's four brightest moons — Io, Europa, Ganymede and Callisto — are visible in even the smallest telescopes with magnifications as low as 25x. Since each revolves around the planet with a different period, ranging from 1.8 to 16.7 days, they form a new arrangement every clear night. Watching them is a delight, like seeing a solar system from afar, with mighty Jove replacing the sun.
As Jupiter rises later and becomes better placed for viewing, we'll explore more things you can see there with a small telescope in a future article.
"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob.
https://www.jamestownsun.com/astro-bob/7027139-Astro-Bob-Meet-Jupiter-a-planet-with-plenty-of-atmosphere
2021-05-14 02:21:00Z
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