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About saac

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  1. A good visual example of a shock wave initiating a change is shown in the video below. Distilled water placed in a very clean bottle (reduces nucleation sites) remains liquid at well below 0 degrees Celsius but freezes instantly when shocked. A similar effect can be seen in hand warmers which use sodium acetate. When heated the sodium acetate reverts to its liquid state but when shocked, usually with a clickable metal disc, the shock initiates the reaction. I may be wrong but I think I remember Brian Cox referring to the physics of dust clouds coalescing under the influence of gravity in one of his programmes. He had a tank of "dust particles" suspended in micro gravity (he was on NASA's vomit comet) and, if I remember correctly, he was showing how the electrostatic force would have inhibited the particles coalescing to form solid chunks. He went on to argue that it would have taken a shock wave to initiate the clumping of the particles. Jim [youtube]
  2. Computer bargain !!

    Thanks for the heads up Skipper Billy, I'm looking for a new desktop myself and I like Dell, well built and reliable. Jim
  3. NASA always get the best shots

    Yeah, but have you seen the mount Jim
  4. Sun HA 19 Sept (+ Frankenscope!)

    Lovely detail there Chris, am I right in seeing some detail on the limb as well. I'm also admiring your focus I've never managed to get the sun as sharp. Jim
  5. Horizon tonight

    Why am I not working for NASA? These people have truly amazing jobs Jim
  6. Horizon tonight

    Good grief, not on here until 2330, too late for a school night . I thought I'd be clever and watch it live on BBC i player on my laptop but that of course asks you to sign in , determines your location and then presents the local programme schedule - not happy Last ditch hope - IPlayer through the Amazon fire stick - bingo we are in and watching - happy days What a palaver, I feel like a Cassini mission controller! Jim
  7. Pier project **completed**

    That looks like a really neat construction, you are going to notice a big difference. Enjoy, once you escape the clutches of the NHS, good luck Jim
  8. 16 " Open Truss Dobsonian Build

    Thanks, Beulah. I spent some time, perhaps too long, looking at different designs before I settled on this. I found a few that used a circular box but the Waite Research design caught my eye. It is a more expensive and time consuming way of doing it (as DIY) vice a rectangular box but it is supremely strong and aesthetically pleasing. I've used FlexiPly in the upper OTA, akin to a monocoque design where the main loads are carried by the ply. First time using FlexiPly and I must admit it's a fun material to use; I need to find something else to build with it Jim
  9. 16 " Open Truss Dobsonian Build

    Paul, Thanks Paul. I'm trying t o emulate the Waite Research design as much as possible although I've had to make some changes due to use of hand tooling and my woodworking skills. I must admit, I do like the look of the circular mirror box, it's my intention that it will also serve as the mirror storage box when off the telescope. The lower OTA , with mirror and cell, is heavy; I haven't got around to weighing it properly yet, maybe do that at the weekend and have a look at the turning moments as well. I fitted the azimuth bearing yesterday and it rotates really smoothly in both azimuth and dec. There is something quite pleasing watching a big scope move around - simple things I know Jim
  10. 16 " Open Truss Dobsonian Build

    Hi Mike, yes this is the monster. I had thought it would have been completed before Euan left but I underestimated the time needed. All being well, it should be ready for the return from the Oct half term. I'm busy looking for a good dark site in the local area for a first light test - Kingsbarns near St Andrews looks promising, good car park site down by the beach. I've got a group of 5th year students itching to get their hands on it so when we are ready to go you and Euan are more than welcome to join us. After that, the plan is to take a trip out to the Scottish dark sky observatory down in Dumfries and Galloway or maybe up to Skye. I must admit, I'm getting quite exited now, I've never looked through a large aperture scope so I'm hoping for a big difference. Jim
  11. Truss scope using 3D printed parts

    Dave, If you do eventually go down the route of the Moonlite connectors all I can say is that you won't be disappointed. They are made from delrin and the quality is excellent. Here is a bit of a wild-card - what about moulding the blocks rather than printing. In the past I've used mouldable plastic material called polymorph (trade name). It's a thermoplastic that can be moulded for small prototyping projects. When it sets it is remarkably hard and (like delrin) can undergo some basic machining - tapped threads etc. The trick of course is to make the moulded shapes true rather than the usual organic form that they take. Dimensional conformity is also a bit of a problem as is repeatability but if you were to use a mould made from say wood of a half block then maybe you could make it work. Jim Polymorph
  12. Truss scope using 3D printed parts

    Dave the connectors will be very much subjected to static loads so I'd hazard a guess that if your test print held up under the load of your car then they should be fine. Just a thought, do you need to print the block in two halfs as shown in your diagram, could you not print it in a single component as per the mooonlite connectors? Perhaps the weakest point might be the threaded portion where the screw reacts as it holds down on the ball. I'd give it a go, set up a proper test, I think you could be onto something. Jim
  13. Horizon 10 Sept

    Thanks for the heads up ronin, I'd have missed that. One for catch up, I do wish they wouldn't put these on so late - lol, I must be getting old Jim
  14. 16 " Open Truss Dobsonian Build

    I also picked up a nice SW 2" EP (28mm) from AstroBoot, I thought it would set off the scope nicely. I'm also keeping my eye out on AstroBoot for a focuser, my own scope is missing its Moonlite now that the sky is getting dark. No real urgency, I still have my ED80 mounted so should keep me happy enough Jim