RS was at II:101.6 deg. (Apr. 4, Einaga), and dark arch surrounded its southern edge. Elliptic oval with vivid orange color can be seen in RS Hollow, having dark core at its center in high resolution images. Dark streak emerging from arch along SEBs edge was prominent between RS and II:40 deg., preceding which weak narrow line extended to around BA. So, whole length of the streak reached about 140 deg. Dark arch of RS was very conspicuous in early April, but it had turned into bridge connecting with SEB, being somewhat declining. This may be because collisions with SEBs retrograding spots came to an end, as there were only two typical dark rings at around II:45 deg. and 70 deg. along SEBs preceding RS, as of the end of April. However, small scale collisions might succeed, because delicate irregular shadings could be seen around RS Hollow and in space between SEBs edge and dark streak described above. Following RS, post-GRS disturbance had shrunken to 20-30 deg. in length, but on Apr. 21, white spot newly emerged at II:156.2 deg. (Miyazaki), and this region became temporarily active.

STBn jetstream became active with many dark spots. The activity of STBn jetstream had started in February 2004, and our section had identified 12 spots with mean rotation period of 9h53m43.8s +- 7.9s (-2.9 deg./day) last apparition. This apparition, jetstream spots came to appear again on STBn preceding BA from February. These spots had typical jetstream speeds of -3.3 deg/day, and leading one had reached around II:160 deg. at the end of April. Since many tiny dark spots were observed on STBn, and STBn itself also darkened preceding BA, activity of this apparition may become more intense than that in last apparition. BA was at II:326.3 deg. (Apr. 21, Miyazaki). It was easily seen through a small telescope, because it was large bright oval surrounded by dusky features. Dark STB extended from BA to around II:50 deg., following which somewhat southerly component (STZB?) was seen up to around RS. In the same sector, SSTB included five long-lived white spots, and this month, leading one was just passing south of BA. Miyazaki indicated that this passage might make BA large and elongated (11.3 deg. in length, Apr. 21). Similar change also observed in January when white spot in STZ had passed south of BA. SSTB white spots was often separated by cyclonic filamentary regions (FFRs), one of which became bright and long this month, more prominent than white spots itself.

Broadened NEB included 6 barges in a little north from the center and 9 small white spot (portholes) along northern edge. These increased from last month, and a prominent array was formed to the north of BA, where three barges and three portholes were aligned alternatively spaced about 30 deg. apart. All these spots newly appeared this apparition except for one porthole located at about II:40 deg. Rogers of BAA indicates that this is the long-lived white spot called 'Z' survived since 1997, and prograding faster than other spots.

NTB was still absent at all longitude, and no forewarning of North Temperate Current-C (NTBs jetstreak outbreak) were seen. But in recent years, NNTBs and STBn jetstreams has been very active, and SEBs jetstream also keeps high activity level. Therefore, we should also keep watch to NTBs jetstream. According to Rogers of BAA, NTZ became partially dusky, and he suggested that it might be a sign of revival of NTB (or NTBn), apart from jetstream activity described above.

(2) Saturn

Saturn passed eastern quadrature on Apr. 10, and had moved to western sky in the evening. This month, we have received observations listed below. One image by Tomio Akutsu made before March was included due to Director's fault.

On Saturn, the region around South Pole showed interesting change. While SSTZ rapidly increased redness in this apparition, the central part of SPR around South Pole became lighter than before, presenting distinct dark green tint, though SPR had been uniformly dusky. Since adjacent STZ had faint green tint, strongly reddish SSTZ was flanked by two greenish zones, showing remarkable contrast.

In SEB where activity of white spots attracted attention, southern half of the belt was faint, while northern component was clear. But aspect of south component varied with longitude. Though between III:200 deg. and 300 deg., it almost faded away and the south of SEBZ could hardly be distinguished from light STrZ, in the range of III:300 deg. over, it was uniformly shaded, where SEB appeared broad, and faint SEBs was seen in images taken under good condition.

This month, any feature moving with planet's rotation was not found, though uncertain records were left by Yunoki on Apr. 9 and by Takimoto on Apr. 29, when he wrote that there was a marking like white spot.

(May 10, K. Horikawa)

[Fig.1] Strip map of Jupiter

Apr. 27-29, created from images by Miyazaki and Kumamori.

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