Because astronomy is one of the ancient sciences we have learned much over centuries of observation. This continuity has also given us a perspective that has allowed us to understand that we live on diminutive planet that is part of a dynamic, even violent solar system.
Take for instance Jupiter's famous cyclonic superstorm, known prosaically as the "Great Red Spot"—though it is anything but ordinary. This mind-bogglingly massive cyclone has been a prominent feature in Jupiter's roiling atmosphere for centuries and is sometimes visible from a backyard telescope under good seeing conditions. With wind speeds at over 250 miles per hour, it is almost three times the size of Earth and estimated to be over 400 years old.
And now there is a sequel, and we have a front row seat for what could be titled: "Son of the Great Red Spot," or as it is being called by scientists, "Red Spot, Jr." Father and son can be seen here and here. We have had our scientific eye on the original for a long time: First observed in the 1660s by Giovanni Cassini and Robert Hooke, it has been continually scrutinized ever since. Present-day astronomers can take highly detailed measurements that earlier generations of observers could only dream of using tools such as the Hubble Space Telescope, Keck and space probes such as Pioneer, Voyager and Galileo. We've watched it long enough to note that it is in a state of flux, and even varies in hue, yet just what makes the ruddy cyclone tick remains a mystery.
Though many massive cyclonic storm systems have appeared in the turbulent atmospheres of the fast rotating gas giants, such as those on Saturn and, most notably and unexpectedly, on Neptune, they have mostly been, like Earth's hurricanes, ephemeral phenomena. What is amazing about a storm the size of Jupiter's Great Red Spot is its longevity. In fact, the Neptunian "Great Dark Spot," spotted by Voyager 2 in August 1989, was no longer visible a few years later.
"Junior" has refocused both scientific and media attention on one of the most fantastic features in the solar system, and on Jupiter itself. Of late, on our robotic visits to the outer solar system it seems more heed has been paid to discoveries about fantastic Jovian—and Saturnian—moon systems than to the planets themselves. Not since the impacts of, Shoemaker-Levy 9, which wreaked such havoc in Jupiter's atmosphere in July 1994, and Galileo's probe, which plowed into the planet in December 1995 in a suicide data gathering mission, has the gargantuan globe itself been the center of attention.
Now we are witnessing the relatively rapid birth of this new storm—"rapid" at least in the scale of astronomical time. Junior's development is not something that has happened overnight: It is a merger of three older storms of a type found in the Jovian atmosphere called "white ovals." They met in a slo-mo collision that unfolded over a three-year period starting in 1998. Smaller and very durable, two of these white ovals had been observed for about 90 years, and the third appeared in 1939.
Having become one, the new hurricanelike storm has grown to about half the size of its elder; the latter having a width about twice that of Earth and measuring some 7,500 miles north to south (about an Earth diameter). Both storms wheel around the planet in longitude as Jupiter rotates, but are latitudinally locked in their own narrow bands in the southern hemisphere. Recently, the newly consolidated storm has been taking on its predecessor's reddish-brown hue. Viewed in near-infrared at a methane absorption band, the new kid on the block is as prominent as the oldster. Observers think that this indicates the junior storm rises above the main cloud deck like the original and that the color change could be the product of material being drawn from the depths of the atmosphere and chemically altered by ultraviolet solar radiation.
Some scientists think Junior's development is a manifestation of climate change on Jupiter; the young storm rides in a slightly more southern atmospheric belt at 34 degrees south latitude, at a point where earlier observations have noted that the movement of heat from the equator to the south pole begins to slow down. This "wall" will most likely inhibit heat mixing and result both in warming in the equatorial region and a polar cooldown.
And because Jupiter is in opposition to the sun this month, it is an optimal time to take a personal look at the grand old orb. You can find it in the southeastern sky as soon as the sun sets: The brightest object in the evening sky right now (save for the moon) it is like a beacon shining at magnitude -2.4 and will be hard to miss. If you have binoculars or, even better, a telescope, take a closer look. The solar system's largest planet will come alive as a world. In fact, even as its own miniature solar system. Your attention will be drawn to the four Galilean moons that you will see in various positions in their orbits around the planet. But look at the monster sphere itself. Depending on your viewing conditions and telescope size, you may be able to see faint atmospheric bands and possibly (if it has rotated into view) the Great Red Spot. It is like visiting Niagara Falls or Yellowstone for the first time—you find yourself grasping their reality, and fantastic uniqueness.
As we witness the birth of a new storm on Jupiter, it demonstrates the value of hundreds of years of humanity's continuous observation of the cosmos. We are possibly seeing how the Great Red Spot—one of the most enigmatic features in the solar system—formed by watching the growth of another in real time. Though Junior may be spawning from different factors and may not become as large (due to the jet streams that bound it into a narrower band than the big storm), we will have watched its development from its birth—and if it takes after its elder, we may be watching this whirling twosome for generations to come.