J. Brit. Astron. Assoc., 108, 3, 1998, p.136
J. Brit. Astron. Assoc., 108, 3, 1998, p.136
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From the Director of the Meteor Section
The interesting account of the Leonids of 1799 as seen from Cambridge, unearthed by Jeffrey Barham (J. Brit. Astron. Assoc., 108(3), 136 (1998)) is not in fact unique. The Leonid storm of 1799 was seen from several locations in the British Isles as dawn broke on the morning of November 11. Research by the noted Scottish historian of astronomy Dr David Gavine has turned up a number of other reports of the event, as seen from Banffshire in Scotland, Hartlepool, Enfield and the New Forest. These were published in learned journals of the day such as The Gentlemen's Magazine. Dr Gavine gave an account of his findings at a meeting of the Meteor Section in Edinburgh in 1991, which was later reported in the Journal (101(6), 366 (1991)). It seems likely that further, similar reports exist in local newspapers of the day, and seeking these out may well be a profitable exercise for students of the history of astronomy.
The short duration of the Leonids at their most intense makes it a matter of fortune, to some extent, for observers at a given longitude to be under clear, dark skies at the time. We can only hope that the favourable circumstances for western Europe in 1999 are met with clear skies. A later-than-expected peak in 1998 might result in high activity being JUST visible from the British Isles as the radiant rises (around 23h local time) on November 17–18, though it is considered more likely that any storm peak will best be seen from more easterly longitudes. As with everything in meteor astronomy, the only way to verify the predictions is to go out and observe! Reports of the Leonids as seen in 1998 and 1999 will certainly be welcomed by the Meteor Section.
Neil Bone
'The Harepath', Mile End Lane, Apuldram, Chichester, West Sussex PO20 7DZ. [bafb4@central.sussex.ac.uk]
From Ms Karen Holland
I would like to clarify a few points from the Deep Sky Section meeting summary that was published in the April BAA Journal. With regard to the search for brown dwarfs in the Praesepe cluster, one of the main incentives for this study was the fact that work in which the Leicester group had been involved, had previously found some evidence that there might be a significant low mass population in this cluster (Hambly et al., MNRAS 273, 505–512, 1995). Brown dwarfs in Praesepe would not be too faint to detect (Pinfield PhD thesis, Leicester University 1997, Chapter 4); it is simply reasonable to collect as much evidence as possible by fully analysing existing data, whilst at the same time, pursuing more expensive and time consuming searches.
Previous work done at Leicester on the Pleiades showed that large populations of brown dwarfs were unlikely to be discovered. However, brown dwarfs do exist in the Pleiades; researchers in the Leicester group recently found the lowest mass brown dwarf discovered to date in this cluster (Cossburn et al., MNRAS 288L, 1997).
Karen Holland
136 Northampton Lane North, Moulton, Northampton NN3 7QW [kho@star.le.ac.uk]
From Mr Peter Norman
I was interested to read Bruce Hardie's Solar Section report for 1980–1989 recently published over two numbers of the Journal (1997 October and 1997 December). It was worth waiting for as it gave a comprehensive summary of the activity from shortly after the high maximum of 1979/80, through the minimum of 1986 and back to yet another high maximum in 1989.
Having been interested in the Sun since a schoolboy in the late sixties, I have over the years looked through the Journals and information provided by the Royal Greenwich Observatory on the largest and most active sunspots. Members will probably know that the definitive authority on sunspot areas was the RGO and their photographic record that extended from 1874 to the end of 1976 was unsurpassed; very few days in the 103-year record were missing, all of these in the early years when the number of cooperating observatories was fewer. It was indeed a sad loss when their programme ceased. However, the IAU resolved that this programme should be taken over by Debrecen Observatory in Hungary, so Greenwich's long continuous record could carry on. Debrecen are continuing using similar equipment and methods to RGO so the results are comparable.
These days, professional astronomers have more important areas of work than measuring and recording sunspot areas and positions, especially as it is now known that activity affecting the Earth environment can be measured and assessed more accurately using other techniques. The Debrecen programme can be seen more as a continuation of a long and historic record rather than a primary scientific concern. Hence they have not been able to devote staff time in the same way that RGO could do and the results so far published are for the years 1977, 1978, 1986 and 1994 only. It is to be hoped that in due course the remaining years will become available. I understand that the volumes for 1978 and 1994 and all future years will only be published electronically; those interested can access them on the World Wide Web at ftp://fenyi.sci.klte.hu.
As Debrecen have taken over RGO's mantle, area measurements published by them are considered definitive. Bruce Hardie quotes some approximate area measurements of some of the larger and more interesting groups observed during the decade in question. I believe these were probably obtained from United States sources such as NOAA. It is worth noting that these US sources publish their results in 'real time' or 'near-real time', which means that they are not of 'research' quality and need to be used with caution. In addition, the US sources rely almost entirely on drawings and I do not think there is any quality control over these. Until the Debrecen results are published, amateur solar observers will have to look to other sources for more accurate area measurements.
Members might be interested to see some data that I consider to be more accurate than those from NOAA especially as the areas are measured from white light photographs, as were Greenwich's, rather than from drawings. These data come from two sources, originally given to me by NOAA, but subsequently by direct correspondence. The two observatories are Osservatorio Astronomico di Roma in Italy and Yunnan Observatory in China. They give information on the largest sunspots observed during Solar Cycle 22 (1986–1996). As if to emphasise the difficulty in measuring sunspot areas, it can be seen that even from two professional observatories working on good quality photographs, there are discrepancies in the area values, which perhaps can be explained by such factors as photographs taken at different times, quality of the photograph and/or observing conditions, possible inclusion or exclusion of spots within the area covered by the group, etc. In all cases, the Yunnan areas are smaller than the Rome areas. The tables include all the sunspot groups that were recorded as exceeding 2000 millionths of the visible hemisphere at OAR, with the corresponding data from Yunnan.
In order to compare the recently passed cycle to previous ones since 1874, the total number of groups whose area at maximum development reached or exceeded 2000msh is given in Table 2. It can be seen that Cycle 22 certainly had a good number of large groups as solar observers will recall. The giant group of March 1989 was the largest since May 1951 and spectacular in the activity it generated; however, both Rome and Yunnan made the long stream of September 1989 larger. If these area figures are reasonably accurate and are confirmed when the Debrecen results are published, the September group will rank as 6th largest in the 120-year record and the March group only a little way below. For those with Internet access, the Rome Observatory Solar Phenomena Bulletins can be accessed via http://oar.rm.astro.it , although I have not been able to locate an Internet site for Yunnan.
Peter C. Norman
69 Cranston Road, Forest Hill, London, SE23 2HA. [peter.norman@virgin.net]
Rome Yunnan CMP Lat. Long. Max Max No. No. area area (Rome) (Yunnan) 9336 88161 1988 Jul 01.9 19°S 005° 3551 2834 9429 88304 Oct 24.1 21°N 295° 2054 1439 9511 89013 1989 Jan 13.2 32°S 307° ? 2144 9514 89019 Jan 15.9 21°N 271° 2029 1757 9536 89054 Feb 11.4 31°N 282° 2151 2059 9564 89105 Mar 12.8 33°N 255° 4125 3598 9654 89262 Jun 14.6 20°N 096° 3201 3054 9733 89381 Aug 17.7 16°N 327° 2464 2361 9747 89410 Sep 05.0 17°S 086° 4493 3842 10031 90243 1990 May 19.0 16°S 311° 2721 2111 10231 90589 Nov 20.0 19°N 026° 3581 3441 10302 91045 1991 Feb 01.2 13°S 142° 2521 2139 10360 91138 Mar 24.7 24°S 183° 3087 3038 10406 91224 May 05.5 09°S 352° 2604 1878 10446 91286 Jun 09.7 30°N 246° 2639 2593 10608 91548 Oct 28.5 11°S 184° 3007 2687 10672 91667 Dec 28.9 17°S 097° 2548 1814
Cycle No. of groups maximum GT 2000msh From Greenwich data: 1883.9 4 1894.1 7 1907.0 7 1917.6 4 1928.4 7 1937.4 17 1947.5 18 1957.9 17 1968.9 11 Estimates from Rome & Yunnan data: 1979.9 11 1989.6 15
From Mr P. W. Parish
Wednesday 22 April 1998
After an overcast start the cloud cleared to leave a pale blue sky. Positioning myself so the Sun was hidden behind my house and using wooden steps as a tripod I located Venus in the 10x50s at 9.30 am GMT. The planet's phase was still just visible, looking like a very tiny white last quarter Moon although I knew it was actually well over fifty percent. About half a degree to the left of Venus, Jupiter was easily visible well in the same field of view. Jupiter's little dull washed out round disk contrasted sharply with the much smaller but considerably brighter semi-circular one of Venus. It was interesting to compare the two planets simultaneously in identical daylight conditions. I tried but could not see Venus at any time with the naked eye although I observed both planets on and off in binoculars until just after midday GMT.
Two days later (24 April 1998) I picked Venus up again in the 10x50s at 6.45 am GMT. Jupiter was still clearly visible in the same field of view but this time between one and two degrees to the right of Venus. They were veiled by thin high cloud which quickly thickened until both planets were hidden. The sky remained cloud covered until 10.10 am when a clear blue mass made a welcome but brief appearance. The blue was richer than on April 22 and Venus was a naked eye object although it was far from conspicuous. Jupiter was invisible with unaided vision but both planets were very clear in the binoculars moving in and out of passing cloud wisps, until more permanent cloud intervened and I ceased observation.
P. W. Parish
30 Wooldeys Road, Rainham, Gillingham, Kent ME8 7NU
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