White ovals of the NEB are anticyclonic [10] and can sometimes be seen on or near the NEBn. When the northern edge of the NEB is receded, the ovals may appear completely in the NTrZ. At other times the white ovals can be seen to protrude into the northern edge of the NEB, forming a bay or large notch in it. Occasionally, a white oval may be seen completely within the northern edge of the NEB, perfectly surrounded by the coloration of the NEB itself. This gives a striking appearance and is often referred to as a "porthole." The long-lived white oval, designated oval "Z," has been observed for some time on the NEBn. This oval was widely observed and reported during the 2001-2002 apparition. Again, features as prominent as this allow long-term observations and provide a good means for determining drift rates at the latitude occupied. Four small, but very bright and prominent ovals were also seen during the 2001-2002 apparition embedded in the NEBn at different locations around the planet. These smaller ovals were prominently absent during the five previous apparitions. Their appearance was a very interesting addition to the belt. Although none of these small ovals were seen or reported visually, they were followed consistently in CCD images for several months of the apparition. The small ovals have now been seen with some frequency in following apparitions now that CCD and webcams are producing images with ever improving resolution.

Although during many apparitions we become used to seeing the NEB as somewhat wide and solid, bright rifts can occasionally be seen running through the belt. Such was the case in 2000-2001 (Figs. 3.5 and 3.9) and even more so during the 2001-2002 apparition. During these two apparitions, many bright rifts were detected on CCD images. Several of these rifts were prominent enough to be seen visually, and I observed several with an 8-inch reflector. The rifts usually extended for some distance around the planet, with lengths of 20-30° not uncommon. Some of the rifts were so visually stunning as to give the NEB the appearance of being split into a north and south component along some segments of the belt. Rifts generally are white spots or streaks with varying shapes near the middle of the belt. They are usually oriented from south-preceding (Sp) to north-following (Nf), sheared as it were by a velocity gradient. During 2004, bright rifts were again prominent running through the NEB (Fig. 3.12). During March of that year, rifts were so prominent in a segment of the NEB as to make the belt appear faded when viewed visually through an eyepiece. Bright rifts can change in shape and length over short periods of time.

Fig. 3.12. Jupiter on March 6, 2004. This webcam image reveals a bright rift running through the middle of the NEB for quite some distance. Note the low contrast of the GRS on the following limb compared to the SEB. Four small ovals are prominent in the SSTZ in this image. The NTB and NNTB are still absent. South is up. (Credit: Donald C. Parker).

Although the NEB does not go through distinct jet stream outbreaks like other belts, it can exhibit variations in its activities in addition to those already cited [11]. Although the color of the belt is generally always reddish-brown to grayish-brown the northern edges have been known to occasionally appear yellowish. The NEB can undergo latitude shifts. Over recorded history, while the southern edge of the belt has been fairly stable, the north edge has varied greatly, especially during the late 1800s to early 1900s. During the 2000 through 2002 apparitions, some segments of the NEB became rather narrow, with the northern edge retreating significantly. And, while the NEB is normally not subject to fading as the SEB can be, it has gone through fadings and revivals (restoration of the belt) in the mid-19th century and early-20th century [12].

During 2006, the NEB was again broad, and was about as dark as the SEB. The northern edge of the NEB was relatively smooth, without large undulations or bays. Long-lived white oval Z was well seen. There were also other smaller ovals, similar to the ones often found in the SSTB, seen embedded in the northern edge of the NEB. These small ovals were difficult to see visually, but were quite prominent in good CCD/webcam images. To me the color of the NEB was a distinct reddish-brown. There were a few darker reddish-brown barges seen in the middle of the NEB at various locations around the planet. There were also distinct bright rifts running longitudinally through the NEB, with a prominent one centered near 89° System II, on an image taken by Donald Parker on 15 July, 2006. This bright rift was at least 50° in longitudinal length and could be seen visually. The bright rift ran through the NEB and its preceding end opened into the EZ at 307° System I (Fig. 3.13). The rift, residing near the southern edge of the NEB, caused the southern edge of the NEB to appear uneven. There were many grayish-blue projections on

Was this article helpful?

0 0
Telescopes Mastery

Telescopes Mastery

Through this ebook, you are going to learn what you will need to know all about the telescopes that can provide a fun and rewarding hobby for you and your family!

Get My Free Ebook

Post a comment