From: TerryMosel@aol.com Date: 12 June 2006 19:38:53 BDT Subject: IAA BBQ, NLCs, ISS all night, Blackrock Castle Obs Hi all, 1. Irish Astronomical Association Midsummer BBQ: Don't forget the social and gourmet (or should that be gluttony?) event of the year: the IAA's annual midsummer barbecue, held in the lovely and historic grounds of Armagh Observatory, courtesy of the Director, Professor Mark Bailey. We start at about 3 p.m., with some activities such as a tour of the observatory, and we hope to have an astronomical treasure hunt as well, with some worthwhile prizes. You can also see the amazing, unique, 'Human Orrery', and maybe the newly restored historic telescopes. And although Armagh Planetarium won't be open to the public for another month or two, you can admire the newly refurbished building from the outside - it's a transformation. We light the fire at about 5.0, with cooking commencing about 5.30. The format is the same as usual: free admission to members and guests (and if anyone else specially wants to come, I don't think you'll be turned away!); you bring all your own consumables, plates, cups, glasses, cutlery etc, and a folding chair or rug to sit on. If you have your own BBQ tools (tongs, fork etc), bring them too. We provide the cooking facility. We have a large gazebo just in case of rain, but we have been lucky with the weather every year so far, and the long-range forecast is good. If it's clear, we'll have some solar observing. It's on SATURDAY 24 JUNE - don't miss it. 2. NLCs: The short summer nights bring few benefits for the amateur astronomer, apart from the warmer temperatures of course. But one is that this is the best time of year to see Noctilucent Clouds, or NLCs for short. 'Noctilucent' means 'night-shining', and these beautiful high-altitude clouds do indeed 'shine at night', often being at their best around local midnight, which in Ireland, allowing for Summer Time, is usually around 01.20 - 01.40 on your watch. But they can be seen any time from about 00.30 to 02.30, if the sky is dark enough, although very near local midnight the Sun may be just too far below the horizon to illuminate them all fully, especially for those living further South. Paul Evans(EAAS) from Larne got some lovely photos of them recently, and one was featured on Spaceweather.com. They are thought to be caused by ice crystals condensing on meteoric dust, i.e. the very fine dust left behind as meteors burn up on entry high up in the atmosphere, or possibly even just extremely fine particles 'wafting in' from space. The reason that they can be seen is that they are so high up (about 80-85 km) that the Sun still illuminates them even when it is too far below the local horizon to illuminate ordinary tropospheric clouds. And this is the best time of year to see them because the Sun never dips very far below the N horizon, even at local midnight, giving the best conditions for seeing them. They can only be seen when the Sun is between 6 and 16 degrees below the horizon. They appear low down near the N horizon, often in the vicinity of Capella, and appear as wispy silvery or sometimes bluish streaks, often parallel to the horizon. Some 'curls' and 'billows' are also occasionally visible. They can be seen anywhere in Ireland or Britain if you have a fairly clear N horizon, but because they occur mainly at latitudes of 60 degrees to 80 degrees, those in the far South don't see them as well or as often. This year may have greater NLC activity than usual, because they are seen more often around sunspot minimum, so do have a look on clear evenings. They are quite easy to photograph, with exposures of 1" - 4" on 400 ISO film (or 2" to 8" on ISO 200 film, etc); or just experiment with your digital camera and see what you get with each trial. Successive photos over a period of half an hour or so may show changes in structure and motion. Do not be fooled by ordinary wispy cirrus-type clouds visible late on a summer evening: the sky needs to be dark enough for you to see the first few brightest stars in order for NLCs to be properly visible. 3. The ISS (International Space Station) is currently visible making a series of 'morning' passes across Irish skies, but at this time of year, as evening twilight merges into morning twilight, it will in fact progress seamlessly into the next series of evening passes without a break. This is because at this time of year the Sun will never be so far below the horizon that it cannot illuminate the ISS as it passes over. So we start seeing 'morning' passes getting earlier and earlier, and then find both 'morning' and 'evening' passes occurring on the same night. Normally we can never see more than two orbital passes of the ISS on any one night (evening or morning): since the orbital period is about 95 minutes, the Sun would be too low below the horizon to illuminate the ISS by the time it came over on its third orbit after the sky got dark enough to see it (or for morning passes, the sky would be too bright by the time of the third orbit). It still passes over of course, but if it's in the Earth's shadow, or in daylight, we can't see it. However, with the Sun never getting too far below the horizon at this time of year, we can sometimes see THREE orbital passes in the one night. From the latitude of Belfast the first opportunity occurs on 16 June, with passes commencing at 00.20, 01.51 and 03.26. On 17/18 June we have passes commencing at 23.28, 01.02, and 02.37. And on Solstice night on 20/21 June, passes commence at 23.01, 00.35, and 02.10 (times may change, and will vary slightly according to your location). Another bonus is that such passes are visible almost from horizon to horizon! In other words, since the Earth's shadow is projected so low in the sky, and towards the South, the ISS stays above it for almost all the time it is above the horizon, and is thus illuminated, and visible. It takes about 5-6 minutes to cross the sky, roughly from West to East, and can appear brighter than any star now visible, and sometimes almost as bright as Jupiter. From Belfast the highest altitude it can reach is about 46 degrees, in the Southern sky, but from South Cork it can pass overhead. A 10" - 20" exposure on your camera will show its motion very well, although beware of over-exposure of the twilight background at this time of year! Check the excellent and free www.heavens-above.com for details for any location. If you are entering your positional co-ordinates yourself, as opposed to picking a town from the huge database, remember to select the 'UK + Ireland' time zone, or it will give you the times in GMT all year round - rather than in Summer Time at this time of year! That site also gives details of lots of other things for your own location, such as Iridium flares, other satellite passes, comets, etc. 4. Blackrock Castle Observatory, Cork: IAA members may recall an excellent talk given by Dr Niall Smyth of CIT several years ago, when he told us that plans had just been approved to restore Blackrock Castle, on the entrance to Cork harbour (S side), featuring a new public/ research observatory facility there. I got an invitation from Paddy Brennan, past Chairman of the Cork Astronomy Club (and IFAS treasurer), to attend the special CAC event there last Saturday, just one week after the official opening by Leo Enright. The restoration has been done very well, there's a nice restaurant in the grounds, and a separate bar for other functions, and they will be adding extra car parking spaces. And although it seems slightly incongruous, there is indeed a dome containing a 16" Meade SCT telescope on top of the highest main turret! This will be operated entirely robotically, and will link up with CIT in Cork itself, and with other telescopes around the world, with terabyte capacity. There will also be another telescope, and a small radio telescope, although it is not in place yet. There is an interactive hands-on science centre, a small conference room, a research area, and of course there will be display and exhibition material. The tour of the castle and observatory by Niall Smith was followed by various talks and telescope demonstrations by members of the Club - with some very impressive equipment! - and there was a free lunch! All told, a very enjoyable day - thanks again for the invitation! Congratulations to Tom Bonner who did most of the organising, and the rest of the Club for their efforts too, including the excellent catering. And congratulations to Niall Smith for bringing the project to fruition - it's well worth a visit if you are ever in the area. It's not open to the public just yet, but watch this space - I'll give further details as they become available. Clear Skies, Terry Moseley.
Last Revised: 2006 June 13th
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