J. Brit. Astron. Assoc., 106, 6, 1996, p. 347-348
(Note: The Association is not responsible for individual opinions expressed in articles, reviews, letters or reports of any kind.)
From the Director of the Mars Section
In my biography of E. M. Antoniadi, published in our Journal[1] and in the Bulletin of the Sociétè Astronomique de France,[2] and also in a history of the Flammarion Observatory, Juvisy, in the 1996 Yearbook of Astronomy,[3] I referred to the exquisite drawings by this famous observer, who directed the Association's Mars Section from 1896 to 1917.
Antoniadi's only extant notebooks relate to the period of his employment under Camille Flammarion, 1893–1902. Until recently I had seen only four large notebooks, arranged primarily by object and secondly by date, clearly copied from the originals on Flammarion's behalf. During a visit in July to the Centre for Planetary and Cometary Documentation at the Meudon Observatory, Mme Neyvoz and M. Boyer showed me (amongst other items of interest) some small 11×17cm softback notebooks of Antoniadi's that had apparently resided in the Meudon archives for some time. This series of ten notebooks covers the period 1893 September 25 to 1897 August 19, though numbers 6, 7 and 9 are missing. The observations, all made at the Juvisy Observatory, were beautifully written up with many pencil sketches and watercolours. The books show that Antoniadi's greatest output was in the year 1894. The notebooks are written in French; as Antoniadi once informed W. H. Wesley that his astronomical observations were written in his native Greek, it is possible that the present notebooks are also copies that had been made for Flammarion's use. I reserve judgement!
Antoniadi's post-Juvisy notebooks are still missing; as I have written elsewhere, they were presumably deliberately destroyed by their originator during the Second World War.
R. J. McKim
c/o The Common Room, Oundle School, New Street, Oundle, Peterborough PE8 4EN
[1] J. Brit. Astron. Assoc., 103(4), 164–170 and 103(5), 219–227 (1993); ibid., 104(1), 8 (1994)
[2] Bull. Soc. Astr. Fr., 108, 308–314 and 341–350 (1994)
[3] In Moore P. A. (ed.), 1996 Yearbook of Astronomy, Macmillan, 1995
From Dr Patrick Moore
Professor John Milburn, of the University of New England, is undertaking research into 'blue Moon' sightings. I have seen a really blue Moon only once: on 26 September 1950, due to vast forest fires in Canada. But I wonder if any other members have seen them? If so, would you be kind enough to let me know, and I will relay the information to Professor Milburn.
Patrick Moore
'Farthings', West Street, Selsey, Sussex.
From Mr Gerald North
I refer to the puzzle set by Mr V. Mayes in the October Journal.
One must be careful when comparing inertial frames of reference. The physical situation of the space-travelling twin A is not the same as that of the earth-bound twin B. Twin A experiences acceleration forces (increasing momentum as a result) at the beginning of the journey, whereas twin B does not. It is true that at the end of the journey twin A experiences retarding forces reducing the momentum of twin A to zero with respect to B's frame of reference once more, but during the journey twin A's physical parameters are altered: length decreases in the direction of travel, mass increases and time dilates.
Twin A experiences changes as a result of experiencing acceleration forces. Twin B is not subject to these same forces, hence the asymmetry in their situations. At the journey's end, twin A really is younger than twin B when the former disembarks from the spaceship.
Gerald North
9 Camperdown Street, Sidley, Bexhill-on-Sea, East Sussex TN39 5BE
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From Dr F. W. Thompson
I sympathise with Victor Mayes' dilemma concerning the Twins Paradox. The explanation is that the basic equations of special relativity apply only to inertial, i.e. non-accelerated observers. For the purposes of the argument, twin B aboard Earth experiences no acceleration, whereas twin A aboard the spaceship experiences considerable accelerations. Hence only twin B is in a position to perform meaningful calculations, using the basic equations.
The paradox has, however, been analysed from the point of view of the non-inertial twin, and agreement between the twins has been obtained. As measured by the travelling twin, small increments of that twin's time, dT, are related to corresponding increments of the stationary twin's time, dS, by the equation dS = (1 + ax1) dT, where a is the acceleration of the travelling twin away from Earth, and x1 is the distance from Earth, as measured by the travelling twin. Thus, for a given acceleration, the effect on the estimate of the stationary twin's time increases, as the distance between the twins increases. Now at large distances, the travelling twin experiences only negative values of a, and at small distances, only positive values of a. It is this imbalance which finally leads to agreement about estimated times.
I hope this outline answers Mr Mayes' question, but for myself, a further paradox arises. Suppose that triplets A, B and C are together in space, remote from gravitational fields. Simultaneously A and C accelerate away from B, in opposite directions. After a time A shuts down his/her forward rocket and switches on the retro rocket. At the same time, as measured by B, C does likewise. In fact, apart from the difference in direction, everything that A does is mirrored exactly by C, as observed by B. Eventually A and C come to rest, relative to B, and then begin to travel back towards B. At an appropriate time, A and C shut down their retro rockets and switch on their forward rockets, so that they arrive back safely and simultaneously to B.
According to the Twins Paradox, both A and C will now be younger than B, each by the same amount. Hence A and C will be of equal age. But at any instant (apart from the instant of turnaround) the speed of A relative to C, and the speed of C relative to A, has always been greater than their speed relative to B. I do not see how the equation given above resolves this paradox, and I would welcome an explanation.
F. W. Thompson
109 Beltoy Road, Carrickfergus, Northern Ireland
From Mr David Greenwood
In the August 1996 Journal, the Director of the Mercury and Venus Section refers to an observation of Venus I made between 18.10 and 18.35 UT on 1985 March 19, and what he describes as late confirmation in the form of a similar observation made earlier the same day by Thomas A. Dobbins. Mr Baum claims that in the absence of independent confirmation at the time, doubts were expressed as to the nature of the appearances, and the observations were discounted.
He fails to point out that the luminous spot projecting beyond the limb was temporary, and that due to poor seeing and its fading, after 18.35 UT it was no longer visible. That is why the observation terminated after 25 minutes. He also does not make clear that there was confirmation of the visual sighting in the form of a tri-colour series of photographs taken with my 18-inch telescope using Kodak TP2476 emulsion in red, green and blue light. The spot was recorded in each waveband, being densest in red. These images were examined using a linear LED scanner and found to be genuine, i.e. the brilliant spot did in fact project beyond the limb.
Dobbins' observation, although on the same day was 19 hours earlier. Mr Baum considers that this observation confirms my own. Perhaps it is a similar phenomenon, but it cannot be the same phenomenon, because in 19 hours the Venus atmosphere would have rotated through approximately 70° and even at the high latitude, the spot-like feature would have been carried over the terminator. Perhaps there was a series of spot-like features, or maybe it was a raised zone at that particular latitude.
Whatever it was, Dobbins' observation is nowhere near as strong a confirmation of my visual sighting as the photographic evidence recorded at the same time and provided to Mr Baum with my report. Would he care to comment on why he discounted these photographs?
J. D. Greenwood
Westgate Observatory, 1 Westgate Avenue, Morecambe, Lancashire LA3 3DW
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Richard Baum replies:
The Greenwood limb anomaly occasioned much interest in 1985. What set it apart from other instances is the care Greenwood devoted to the observation, all of which I reported in detail at the time. Five years later Dr John McCue published the results of his very thorough analysis, to which the interested reader is directed. It was concluded that Greenwood had quite possibly seen a localised bright spot, a not uncommon feature.
However the failure to reach any certain conclusion led many in private to cast doubts on the validity of the observation, something to which I objected. Greenwood I know is a careful observer. He should know therefore that his report would not have been sanctioned by so much attention if its credentials were in any way in doubt. The recent report is centred on the Dobbins' observation because of its associated interest and is written in context, so of necessity it also embraces the scepticism earlier accorded the Greenwood observation. Technical details were not repeated but the original report was referenced for the benefit of those interested enough to follow up the story. It is Section policy to record the unusual when the report is known to emanate from a reliable source. The Greenwood/Dobbins anomaly is on record. That it still awaits an explanation is in the nature of the work.
All we can say of this observation is, that for one very brief moment in time two observers (Dobbins and Greenwood) witnessed something of unusual interest in connection with Venus, and that each perhaps saw a different stage or part of what most likely was the same phenomenon. To say more would be imprudent. In conclusion, David Graham has recently written of a report submitted to him in 1985 when he was Director of the Planetary Section of the JAS, which he suspects may be further confirmation of the foregoing. Attempts are being made to locate that observation.
Richard Baum
25 Whitchurch Road, Great Boughton, Chester CH3 5QA
From Dr John Mason
I should like to make it clear to all BAA members that, despite implications to the contrary, I am not involved in any editorial capacity with a new monthly periodical called Modern Astronomer, published by Chesterwell Management Limited.
John Mason
51 Orchard Way, Barnham, West Sussex PO22 0HX
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