John Deans
A Transient Lunar Phenomenon (TLP) is any strange flash, glow or obscuration, lasting for seconds, minutes or perhaps hours, on the lunar surface. Members of the BAA Lunar Section have been interested in TLPs since they became 'respectable' in 1957 when the Russian professional astronomer Kozyrez obtained the first spectrograph of a TLP.
In the mid-1970s, the BAA Lunar Section ran a network of TLP observers throughout the British Isles with a few observers also in the Low Countries. If any observer witnessed a suspected TLP, he/she would set the observing network in action by telephoning the co-ordinating team at Mills Observatory, Dundee. (Incidentally, in common with Orwell Park Observatory, the Mills Observatory houses a 26cm refractor.) The co-ordinating team would then contact as many observers as possible (including experienced observers such as Patrick Moore) to make as many observations as possible of the suspected TLP. Observers would make drawings of the TLP and take photographs and spectra.
During 1975, members of OASI observed suspected TLPs, as reported below. Unfortunately, ultimately none of these observations turned out to be of true TLPs.
21 - 24 February 1975
During the period Friday 21 - Monday 24 February 1975, the BAA network of TLP observers was a hive of activity! A suspected TLP was observed on the Friday night and Saturday morning, and the network swung into operation. There was a suspected TLP a short distance from the crater Aristarchus. Several observers, notified by the network, confirmed the existence of the TLP. The following evening there was another TLP - this time a blue colouration inside the crater Aristarchus. Howard Miles, who was alerted by the network, not only confirmed the TLP in Aristarchus, but discovered another TLP at the same time in the crater Gassendi, which other members of the network confirmed. On the Monday evening, activity was still visible in the area of Aristarchus. Most observers were clouded out on the Tuesday evening.
The number of observations of the Moon during the period 21 - 24 February received by the BAA Lunar Section left little doubt that there had been major TLP activity in and around Aristarchus. Note that Full Moon and perigee occurred almost together, Full Moon at 01:15 on 26 February and perigee at 22:00 on 25 February. The combined maximum gravitational influence of the Sun and the Earth on the Moon may have contributed to triggering the TLP.
At Orwell Park Observatory, three members of OASI, Charles Radley, Tom Cardot and Dave Barnard observed the suspected TLP in Aristarchus and submitted a report to the BAA. However, by February 1976 (i.e. one year later), Charles Radley had concluded that the suspected TLP had in fact been a false alarm.
18 - 19 June 1975
On the night of 18-19 June 1975, Royston Cheesman (OASI Chairman) and David Barnard were observing the Moon with the 26cm refractor at Orwell Park. They saw a strange object near the crater Clavius, which they described as looking like a ten story block of flats. The object stood prominently near Clavius, casting a shadow towards the crater. Roy and David, together with Stephen Flory, made another observation on the following evening using Roy's 210mm reflector. Although the object was still visible, it had developed dark, radiating arms as though an eruption had occurred and lava had poured out. Shortly after 1:00 am, after about half an hour of observing, the Moon had moved out of view behind a house, and Stephen and Roy had to dismantle the telescope and move it together with its stand into the front garden.
Roy and Stephen then contacted a member of the BAA TLP network, Commander Henry Hatfield. Commander Hatfield was having a cup of tea at the time, waiting for the clouds to clear over his observatory, and took the call.
If the object were merely a formation on the lunar surface, it should be visible again under similar conditions of illumination. The selenographic colongitude is given against the sketches of the object below. In August 1975, approximately the same conditions of illumination will arise as follows, enabling observers to check whether the object is a permanent feature of the lunar surface:
Colongitude 15.5° on 16 August at 21:30 UT
Colongitude 27.3° on 17 August at 20:45 UT
Later, Roy sent his drawings to Patrick Moore for evaluation. Patrick replied to the effect that the feature was a depression which was not obvious in the usual way and which Roy and his colleagues had observed at the time when conditions were favourable.
Roy reported that when the selenographic colongitude of the feature was the same as before, on 16 August, he had to wait until 23:00 for a break in the cloud before he could observe the Moon again through his 210mm reflector. The break in the cloud permitted only a few minutes viewing but the feature appeared to still be present.
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J Appleton
Original: Newsletters April, August 1975; February 1976 Updated 05 August 2009 |
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