Jupiter in 1949 & the Revival of the South Equatorial Belt

2022 January 29

Richard McKim

Until now there has never been a comprehensive account of Jupiter’s 1949 apparition, in which there was a Revival of the South Equatorial Belt (SEB). On opposition day, Jul 19, despite the SEB south component not having faded to invisibility, the first white spot of the Revival was seen. The spot had originated within a pre-existing SEB(S) dark ‘barge’, close to the longitude of E. J. Reese’s ‘Source B’. The Revival led to a fading of the initially conspicuous Great Red Spot (GRS), and the development of the Red Spot Hollow (RSH). The S. branch of the Revival was weak, with small retrograding dark spots which failed to pass the GRS, although their velocity was typical. The N. branch was also less active, with some prograding dark spots passing only slightly beyond the GRS/RSH, which also exhibited a typical drift. On the other hand, the central branch was unusually active, with a succession of long-lived white spots and dark columns (mean drift rate Δλ₂ = –67°/30 days). The p. end of the Disturbance in the SEB Zone faded before reaching the RSH. In addition to darkening the SEB, the Disturbance gave rise to slowly-prograding dusky columns in the S. Tropical Zone. Other features were the continuing presence of the S. Temperate white ovals, a very active Equatorial Current, dark spots at the N. edge of the North Equatorial Belt and at the S. edge of the North Temperate Belt, and a dislocated section of N. Temperate Zone. Accurate photographic belt latitudes fill another gap in the literature. We also provide the first colour images from 1949, by compositing filter photographs from the Lowell Observatory, Arizona. That the vast majority of longitudes were obtained at the eyepiece reminds us of the great value of visual observation in providing the foundation of so much of our knowledge about Jupiter.

Introduction

At opposition on 1949 Jul 19, Jupiter had a considerable southern declination of –21°, though its meridian altitude had improved a little since 1948 (opposition Jun 15, declination –23°). Apart from a short account by the discoverer of the South Equatorial Belt (SEB) Revival,¹ this important opposition was never discussed in BAA publications,² while an Association of Lunar & Planetary Observers (ALPO) report published years later was based upon insufficient longitude data for the Revival spots.³ Despite the exceptionally long interval it is thought by the author of this paper that a detailed account would still be useful, for the 1949 Revival had some unusual aspects that should be put on record. Furthermore, there are very few published Jovian belt latitudes for the years between 1947 and 1951, and reliable data to fill the gap are available.

The low altitude of Jupiter in 1949 dictated that the best observations would be made from outside the UK. The majority of longitude measurements were obtained from central meridian transits, and the bulk of these were made by three American BAA members using comparatively small reflectors: W. H. Haas (Albuquerque, New Mexico), E. E. Hare (Owensboro, Kentucky) and E. J. Reese (Uniontown, Pennsylvania). Reese had just been appointed as the ALPO’s first Jupiter Recorder and obtained 1,570 timings. Scans of Haas’ and Reese’s notebooks (archived in New Mexico State University Library) have enabled access to all of their detailed notes.⁴ An equally valuable set of observations was made with a large aperture by the discoverer of the 1949 SEB Revival, R. A. McIntosh (Auckland, New Zealand),¹ while other good southern hemisphere work was carried out by F. M. Bateson (Rarotonga, Cook Islands). Taking advantage of his low latitude, S. Murayama (Tokyo, Japan) also made a long series of drawings and transits.⁵ Some observations were also contributed by G. Ruggieri (Venezia, Italy).⁶

In the UK, observations were contributed to the Section by G. E. D. Alcock, W. F. C. Blumer, J. M. A. Danby, Miss M. Davies-Scourfield, W. E. Fox (who made the largest number of domestic central meridian (CM) transit measurements), F. Perry, H. Wildey and T. W. Williams.⁷ A small number of additional data were gleaned from the papers of the UK observers F. J. Acfield, L. F. Ball and E. H. Collinson.⁸ Artistic drawings were made by Alcock, Ball, Collinson and Wildey.

To supplement these data, we referred to publications by J. H. Focas (400mm OG, Athens Observatory),⁹ and to the original observations of C. F. M. du Martheray (Geneva, Switzerland),¹⁰ both former members of the Section. We also had access to useful observations by W. Löbering in Germany,¹¹ and to many excellent unpublished photographs by Dr E. C. Slipher at Lowell Observatory. From the latter we could prepare some colour composites.¹²

Observations covered the period 1949 Feb 7 to Dec 20. Most of the colour estimates were made by Haas, Löbering, du Martheray, McIntosh and Reese, and intensity estimates by Reese: see Table 1. Belt latitudes were measured from the best photographs (Table 2).

This report is a sequel to that for 1948,¹³ which was published soon after the opposition. At that epoch the BAA reports were numbered chronologically, and this is therefore the 36th report of the Section.

The observations

Colour and intensity estimates are summarised in Table 1. Table 2 presents belt latitudes, while tables of drift rates and rotation periods follow the general text. To conform to the style of Jupiter reports from that era, longitudes of features in Systems I and II are indicated by λ₁ and λ₂, respectively, while Δλ₁ and Δλ₂ denote drift rates in degrees per 30 days (hereafter °/mo). CM1 and CM2 denote the longitudes of the central meridian according to Systems I and II.

North Polar Region (NPR)

Visual observers could detect a North North North Temperate Belt (NNNTB) within the polar shading, and high-resolution photographs taken at Lowell Observatory in July show at least one more belt to the north. It was possible to establish a tentative drift rate for one dark spot (shown in Figure 2C) in the NNN Temperate Current.

North North Temperate Zone (NNTZ)

The zone was somewhat shaded for the most part. A small, bright white NNTZ oval was photographed at λ₂ = 343° by Slipher on Jul 12 (Figure 1). A large but faint white oval was photographed at λ₂ = 003° on Jul 9, while another located at λ₂ ~ 210° was photographed on Jul 15 & 18 and Aug 16 (Figures 1 & 2B), as well as being confirmed visually by Murayama, Jul 16 – Aug 11 (Figure 8). The latter oval interrupted the NNTB.

North North Temperate Belt (NNTB)

The belt contained a number of long dark sections that were nearly stationary in System II (with drifts typical of NN Temperate Current A), two of which almost certainly continued into the next apparition.

North Temperate Zone (NTZ)

For the most part a light zone, the NTZ was shaded within one section containing a North Temperate Disturbance (or N Temperate Dislocation; NTD).

For several months the NTD existed as a sector some 70° long, within which the normal pattern of belts from the NTB to the NNTB was interrupted. At λ₂ = 102° (opposition), the NNTB – or a southern component of it – abruptly moved southwards, widened and darkened to form a conspicuous NTZ Band (NTZB). From here, the normal NNTB was either absent or faint, but it reappeared or intensified towards the following (f.) end of the dislocation. The NTZ between the NTB and NTZB was also darkened within the NTD. At λ₂ = 174° (opposition), the dislocated section was terminated by a conspicuous white oval lying between the NTB and NTZB (Figures 1 (Jul 15 & Aug 16), 2C, 6, 12 & 13), following which the NTZB exhibited a slight ‘step-down’ (less evident after early July) to unite it with the NNTB. A similar step was observed in 1972–’75.¹⁴ Just following this longitude, the NNTB was interrupted during July–August by an NNTZ white oval, previously mentioned under ‘NNTZ’, and following the oval by means of another small step-down (Figures 8, 13 & 17) the NNTB finally regained its canonical latitude.

The f. end of the darkened section of NTB and NTZB had first been recorded by Reese on May 6, but a definite preceding (p.) end did not appear till Jun 6, with the white oval at the f. end being the last component to appear, on Jul 3. The dislocation and white oval, together with the p. end of a lighter section of NTZ located outside the NTD, all moved with positive drifts typical of N Temperate Current A.

In mid-August, the white oval at the f. end of the NTD was in conjunction with a white oval that interrupted the NNTB (see previous section). After then, the NTD faded, with the p. and f. ends of the dark sector infrequently recorded, and the white oval last observed on Sep 10. The p. end was last recorded on Oct 3; a well-defined f. end was last seen on Aug 26, but it continued at the extrapolated longitudes in the form of an NTZ dusky column on Sep 22 and an NNTB dark spot on Oct 19.

North Temperate Belt (NTB)

This was a well-marked belt. An NTZ disturbance involving the NTB was described in the previous section.

On Nov 11, Murayama drew four tiny well-defined dark spots (Figure 23) just south of the S. edge of the NTB between λ₂ ~ 14 to 68°. These looked like NTB jet-stream spots, and he confirmed the activity on Nov 18. An earlier drawing on Nov 6 showed a single, less well-defined feature towards the f. limb, located at λ₂ ~ 99°. The spots did not endure, but good observations so late in the apparition were very few: no drift rate could be inferred. In an interim ALPO report, Reese mentioned that D. O’Toole had also observed them.²

There had previously been a substantial outbreak of NTBs jet-stream spots in 1939–’40, and sparser activity until 1943, but no record in subsequent years. Rogers (2017) notes that Revivals of the SEB and NTB are sometimes associated in time.¹⁵

North Tropical Zone (NTropZ)

This was always very bright, and its S. part contained a number of white spots adjacent to or indenting the N. edge of the NEB that moved in the N Tropical Current. A thin, elusive N Tropical Zone Band (NTropZB) was occasionally seen visually (Figure 9) or photographed by Slipher (particularly on Jul 12; see Figure 1).

North Equatorial Belt (NEB)

The NEB was broad and dark. It was not obviously double, though some sectors had darker edges. Its reddish-brown colour was strikingly intense to Reese in July.

NEB(N): This showed several projections into the NTropZ, a few being more prominent dark ‘barges’, of which No. 11 exhibited a ‘tail’ to du Martheray, June–July. There were a few well-defined and enduring white bays (as in 1948), for which reliable drifts could also be established.

NEBZ: The NEB interior showed several rifts – as in 1948 – that moved at a rate intermediate between Systems I and II. Two were well-enough observed to derive good drift rates.

NEB(S): The S. edge of the belt was extremely active, with many festoons joining the EB, and some continued to the N. edge of the SEB in places where the Equatorial Belt (EB) was absent. There were also numerous white spots in the EZ(N), against the S. edge of the NEB. The festoons and EZ(N) white spots showed similar small negative drifts in System I, and the general appearance of the chart was one of regular motions across all longitudes.

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