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saac

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About saac

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  1. Good episode, well worth watching. Loved the kangaroos running around the observatory for reasons unknown - couldn't help think they were doing it just because it was fun
  2. I forgot about that Alan, good reminder Agree re Jim Al-Khalili, one of my favourite presenters; he has a natural authority about him but it doesn't prevent him getting across the joy of his subject. Jim
  3. Watching now, number 2 daughter has already instructed "dad we must go to Australia next year so we can see the centre of the galaxy". That's next year's holiday sorted then I love hearing the lore of different cultures and the Aboriginal astro lore is so interesting. I think it's a really good move doing an episode from the southern hemisphere, lots to learn. Jim
  4. If only all of my astro related equipment was as useful as my trusty DSLR then I'd have a much easier time justifying purchasing kit. I'm sure there will come a time, once I have the skills to justify it, that I may contemplate paying £1000 plus for a CCD imaging camera. But it won't ever be an easy decision given the restricted use it will get. Until then, I'm going to celebrate the versatility of my DSLR, holiday snaps and all - after all they are way better than my astro images Jim
  5. My main objection is the questions it raises on the shape of universe - maybe I'm using the wrong balloons Jim
  6. "Became inflated over time" Jim
  7. I tend to avoid its use in class, the students have a tendency to read too much into it; they end up stretching the analogy too far and this introduces persistent misconceptions. For those who like the balloon analogy then this article is a useful starting point to identify its limits. The Good Bad and Ugly Of The Balloon Analogy Jim
  8. That shows the danger in reading too much into models like the balloon analogy, like all models it comes with limitations. The trouble is these models become popularised and too often little priority is given to describing the points at which the model breaks down. Jim
  9. Alan I think we also have a problem with our carbon nano tube string! In the style of XKCD - Rotating with an angular velocity of 0.2 rad/s (approx 2rpm) to give a tangential speed of c at 100 million miles would require a centripetal force of around 2.6 x10^13 N. This ignores the mass at the end and has the mass of the string distributed at 1g per km (i've been conservative I think). I've also assumed the mass of the string itself to be distributed at the centre - now bear in mind it is late and my brain has been awake too long today, but 2.6 x10^13 N is a lot of apples for even a carbon nano tube to hold. I suspect that the electromagnetic force holding the carbon atoms in sublime formation in the string would have long given up the battle (requires peer review) Of course I accept no responsibility for my calculations, anyone twirling a 100 million mile carbon nano tube string above their head with a mass at the end should know better Jim
  10. I bet it is so only when we observe it, the rest of the time I bet it's really simple Jim
  11. I've seen this type of question asked but where the broom handle is replaced with a more manageable laser beam or shadow. The question being would it be possible to have the laser beam (at a suitable length along its path) trace out an arc with a tangential velocity greater than the speed of light. A similar version concerns casting a shadow across the face of the moon using a powerful (hypothetical) searchlight projected from Earth. The shadow is cast on the moon by moving a hand across the searchlight beam - move the hand quickly enough and the resulting shadow moves across the surface of the moon with the leading edge moving faster than c. On first inspection, the speed of the shadow's front appears to challenge what we know about the ultimate speed limit c but that is only because when we talk about the speed limit we generally only paraphrase what it actually means. In the case of the moving shadow, or laser beam, no "information" is said to be moving faster that the speed of light so the universe is still safe. These questions are great because they really do tease out understanding of c. Having said all that I hope I've remembered the details of the examples correctly. Jim
  12. I seriously considered hiring a cable detector from HSS when I buried my obsy power cable last year. The trench was 600mm deep and I was convinced I was going to find a drain pipe or power cable. In the end I just took things at a sensible pace - no wild swings of the pick axe, cleared the depth with a spade first (trenching tool). Really satisfying when it was all done but hard work too. Jim
  13. Well if we put our heads together we should have life cracked by tea time then we can sort out cold fusion. The only thing left of any interest after that is to explain why toast always lands butter side down Jim