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Guildford Astronomical Society

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Sent in by John Evans (GAS President).

You know the feeling. You step outside at sunset to look at the sky. All afternoon it has been cloudy with frequent rain and now the sky is perfectly clear. Against the deepening blue, Venus shines. Vega and Arcturus are beginning to appear.

Image: CHRIS HOPPER (click to enlarge)

You recognise at once that a) you are asleep and enjoying a wish-fulfilment dream, or b) you are dead and have made it into amateur astronomy heaven, or c) everything is real but the clouds are just hiding. As soon as you have driven the ten miles to your dark site and set up - but not until then - they will slide out and bury you under a big grey mattress for the rest of the night.

This time it wasn't like that. On the night of August 12-13, several of us gathered at Albury Heath to find the sky beautifully clear from horizon to horizon - and that's how it stayed until we left around 2.30 DST. Tracking several weather forecasts, John Axtell had suggested holding fast to the original plan to meet on Sunday. Theoretically, this was to be the best night for seeing meteors. The night was moonless and the predicted Perseid maximum was due in the early hours of Monday morning. Saturday night had already been tantalisingly clear. Either way, John assured us, it wouldn't have mattered. If it had been cloudy on the Sunday, he would simply have re-arranged for us to meet yesterday. Hmmm....

Those present at Albury were, in alphabetical order: John Axtell, John Evans, Alan Forno, Chris Hopper, Ken Lindup and his wife, Nick Parker and John Slinn; and, arriving later, Gavin Stacey and friend. Most of us had brought film or digital cameras in the hope of capturing meteor trails. Some of us had also brought binoculars and small telescopes for some interim observing. In this context, 'interim observing' means having your eye glued to the eyepiece looking at something you've seen dozens of times before while the most spectacular fireball of the night processes across the sky. We did some of that....

Image: NICK PARKER (click to enlarge)

When we arrived it was already fairly dark. Red Antares and the stars of Scorpius, with Jupiter in their midst, glowed above a pellucid southern horizon. With unusual clarity for this observing site, we could see the teapot' of Sagittarius and the nearby brilliant star clouds, the 'steam' from its 'spout'. The broad overall structure and dark lanes of the Milky Way were clearly visible, north from Sagittarius, past Aquila, through Cygnus and Cepheus and, as the night rolled on, into Perseus and Cassiopeia. Later, M31 and the Double Cluster would easily be visible to the naked eye. Albury veterans (ahem) said this was one of the best nights they had seen there. At around 22.30 DST, we estimated the visual magnitude of the faintest stars in the darkest parts of the sky as around 5.7. This was broadly confirmed later by our count of stars in the Square of Pegasus. The early hours of the morning saw some slight deepening to perhaps 5.9.

On such a transparent night, it would have felt remiss to focus on observing meteors to the exclusion of everything else. John Slinn's 11x80 binoculars gave nice views of some of the bright southerly Messier objects such as M8. Ken's fine Televue NP101 and my own William Optics 80mm apo also performed very well and, as you would expect, with a low power eyepiece, gave marvellous views, for example, of the Milky Way through Cygnus and the brighter, extended DSOs like M31. All of us were impressed by the view of the Double Cluster through Dave Gilbert's (a visitor) Leviathan 25x100mm binoculars - simply breathtaking. If low power scanning of the sky is what you like to do best, start saving now!

Image: John Axtell
ISS passing overhead
(click to enlarge)

We had come primarily to enjoy the meteors and perhaps make some informal records of what we saw - not with a view to conducting systematic research. Most observers had come well equipped for this, with recliners to relax on while looking up at the sky, warm togs and something sustaining in a flask. John Slinn kept us going through the small hours by sharing his cheesy bites and peanuts, and for this we were more than grateful!

John Axtell kept notes on the meteors he personally observed. He counted 36 meteors during our approximately 4 hour watch, but adds that he missed many that others reported. His sightings included two fireballs of estimated magnitude around -3. Both were observed low in the south-east from our location and moving at a relatively shallow apparent angle to the horizon. Generally, the meteors we saw that were most reliably identifiable as Perseids were relatively fast moving and yellowish to yellowish-white in colour. The images captured with consumer digital cameras tended to show them as bluer than the visual impression. Many left clear but short-lived trails - around 5 seconds for the most persistent ones. John Slinn reported hearing a sound as one meteor passed but this was not confirmed by other observers - maybe his ears are sharper than ours! We estimated around 20% of the naked-eye meteors we saw to be mag 1.5 or brighter. Our estimate of a mean hourly rate for naked-eye meteors during our observing period would be around 15, but since our attention was often elsewhere this is certainly an underestimate. There was no obvious build towards a maximum at the predicted time - in fact, the highest incidence of meteors that we observed was probably in the hour between midnight and 1 am DST. This is broadly consistent with an observation by Mike Maunder who noted in an email to Nick Parker his impression that there was no peak at 3am BST and that it occurred about 2-3hrs earlier.

Image: NICK PARKER (click to enlarge)

James Wilhelm observed from his balcony at home and reports that, though he was observing through the lights and haze of the city when looking south, he could clearly make out the stars of Sagittarius and had a good view of the southern part of the sky. He was outside from 23.00 to 01.00 and recorded an average of one meteor every 2.5 minutes, suggesting that our rough count at Albury was indeed an underestimate - a consequence, perhaps, of James being rather more rigorous and systematic in his approach! Our excuse it that we had lots of interesting things to look at through our binoculars and telescopes and spent a lot of time congratulating ourselves on how spectacularly good the night was! James commented that the brightest meteors he saw occurred before midnight - many were bright and left a short-lived trail - and that the rate was higher around 23.00 DST than towards the end of his observing session.

At Albury, as the night rolled on, quiet conversation and the regular clicking of camera shutters were punctuated by occasional gasps and cries of 'Did you see that one?!' Dim red glows moved in the half-darkness as observers adjusted settings, visited others' telescopes ... or fumbled for a dropped biscuit. From time to time, the screens of digital cameras flared briefly as images read out. More often than not, these showed stars against an orange-brown sky background, the characteristic rendition by most digital cameras of the night sky in all but the most pristine and unpolluted places. But several of us had success. Chris Hopper was the first to 'catch' something with his Canon 400D working at ISO 800 on a static tripod.

Nick Parker was the most successful of all of us in capturing several trails with his Canon 350D. He reports that he used a 50mm lens working at f1.4 and 30 second exposures at ISO 100. Do not believe anyone who tells you that the days of film in astro-photography are over - but, for this type of work, the astonishing sensitivity of the digital camera takes some beating. John Slinn was using a digital camera and John Axtell his 'classic' Olympus OM1 with fast colour print film loaded but, as far as I know, they snared no meteors. John did however get the ISS and Endeavour as it passed brilliantly overhead at mag -2.4 and, later that night, visually observed the iridium flare at a prodigious mag -8!

Somewhere in the woods that ring the Common, a vixen barked and screamed. Low in the south, Fomalhaut, most southerly of the first magnitude stars visible from the UK, flashed and flickered. In the east, the Pleaides were rising and, following them, Mars and Aldebaran. It was easy to forget that we were only a few miles from the city centre. The unusually good transparency and absence of low cloud had helped to make the urban glow from the north-east largely unobtrusive. By now, most of us were beginning to feel the chill of a longish night and the instruments were becoming heavily dewed. As most of us left and drove away, the sky was still perfectly clear with just the beginnings of some low level cloud in the extreme south. Our observations of the Perseids would not do much to advance serious research - but it had been a truly memorable night.