In April, new activity was noted on northern boundary of NEB. This apparition, NEBn edge somewhat receded, showing belt itself narrow, and almost barges which had been observed last apparition were disappeared, though it showed violent rift activities in its interior. This activity was triggered by isolated dark spot in NTrZ formed late March at II:345 deg. and new rift activity in NEB. During April, NEBn edge expanded northwards with largely disturbed northern part following the above longitude.

It is well-known that the latitude of NEBn edge shows periodically change and major NEB broadening was observed in 1988, 1993, 1996, and 2000 as recent examples. Therefore, this activity must be new NEB broadening. In this apparition, the latitude of NEBn edge was generally at +18 deg., while in broadened sector, it was at +21 deg. expanding 3 deg. to the north, where NTrZ was very narrow.

Einaga's image taken on Apr. 25 showed that dark projections developed to the north turned to the preceding direction at +21 deg. in latitude, and formed new northern edge of the belt, presenting singular spectacle with saw-toothed and hooked dark markings leaving light spaces between them. These markings may transform into new barges and white spots in the future. The broadened sector ranged between II:340 deg. and II:90 deg. at the end of April, it will rapidly spread in other longitudes and complete wide NEB within several months.

EZs/SEBn disturbance which attracted attention from late February to early March by largely disturbing SEBn preceding RS had encircled the planet, and SEBn rift as the opening into EZ came back in the region preceding RS around Apr.10. Unexpectedly, northern half of SEB did not be disturbed as it prograded the region. The rift reached around II:300 deg. at the end of April (In System I, it was at about I:155 deg. with retrograding motion). SEBn rift was a minor but stable feature forming shallow bay on SEBn edge. Such aspect resembled that observed during second half of 1970s and first half of 1980s associated with EZs oval, but this time, no oval was observed at all.

Activity of mid-SEB outbreak had almost ceased remaining weak white spots spanning about 20 deg. in longitude following RS. On Apr. 16, however, new white spot appeared in SEBZ at about II:145 deg., and became extremely bright and prominent on Apr. 18-20. After then, the spot was disrupted as prograding, but another spot appeared from original position at end of the April. These spots were formed within a narrow white strip trailing from the region of mid-SEB outbreak, only 20 deg. apart in longitude. Therefore, this activity was not new mid-SEB outbreak, but reactivation of original outbreak took place early stage of the apparition.

On NTB, an appearance of tiny white spot was reported by Miyazaki on Apr. 25 (I:85 deg.). This spot resembled initial aspect of the leading spots observed in early stage of NT Current-C in 1990. Though it was expected that within a few days, it might develop much brighter and new activity of NT Current-C might start, it soon disappeared. As NTB is still faint at all longitudes and the belt is in pregnant stage for new NT Current-C activity, we should pay attention in every observation whether bright spot or dark spot appears on NTB.

(2) Saturn

Saturn is in the final stage of the apparition, gradually losing altitude in the evening west sky. This month, we have received observations listed below. As condition got worse, the amount of observation became fewer.

Saturn was quiet this month, too, no feature like spot was observed.

In recent years, Saturn has apparently been seen completely surrounded by its ring, but apparent north-south width of the ring will become smaller than diameter of its body from next apparition. Because such aspect cannot be seen for next several apparitions, we should enjoy it in this apparition to the full.

(May 9, K. Horikawa)

[Fig.1] Singular spectacle of NEB and SEBn rift

Return to OAA Top