Jupiter's giant "eye," the Great Red Spot, stares outward from the planet in this 1979 image from the Voyager 1 spacecraft. The spot is the largest storm in the solar system, and may have been swirling since the 1600s or earlier. In recent decades, however, it has been shrinking; today, it's only about half as wide as in this image. Planetary scientists aren't sure whether the Great Red Spot will rebound or dissipate. [NASA/JPL/Björn Jónsson (IAAA)]
Great Red Spot
Astronomers have been looking at Jupiter through their telescopes for more than four centuries. And for a good bit of that time, they’ve seen Jupiter staring right back. The giant planet’s most prominent feature is a gigantic storm system that looks like a bloodshot eye — the Great Red Spot. It’s the biggest storm in the solar system — wider than Earth.
It’s also the longest-lasting storm — although just how long it’s been around isn’t certain.
Robert Hooke reported seeing a large, oval-shaped feature on Jupiter in 1664 — exactly 350 years ago. Its size and location match those of the Great Red Spot, although there was no mention of its color.
Jean Dominic Cassini saw the same spot the following year, and tracked it for a quarter of a century. After that, however, the next mention of the spot didn’t come until the 19th century.
That means there’s a bit of uncertainty about what Hooke and Cassini actually saw. It could have been the Great Red Spot, or it could have been a smaller storm system. In either case, the Great Red Spot has been spinning away for two centuries or longer.
Despite the many years of observations, a lot of mysteries about the Great Red Spot remain. In fact, astronomers aren’t even certain about what’s responsible for its color. More about that tomorrow.
Jupiter is just beginning a year-long arc across the night sky. The brilliant planet is low in the east at first light, a little above even brighter Venus.
Script by Damond Benningfield, Copyright 2014
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