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661-pete

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Everything posted by 661-pete

  1. Certainly go - and I hope the awful British weather smiles on you just this once! Does it have to be a one-off? Can you not get to a reasonably dark location within a reasonable distance of your back yard (I presume you have means of transporting your Dob around). Check out some local rural sites. Get advice from others who live in your area.
  2. I think we've got a bit distracted from the serious side of the OP by all this 'dark side'/'far side' mixup - which is simply that, a minor semantic slip. I may have been one of the 'poopoo'ers of the earlier thread, if so, I hope it wasn't taken personally! Just that I think it's now become easier, logistically speaking, to put a big optical telescope out into space, where it doesn't need a drive and doesn't suffer from gravitational flexing. But if we want a radio telescope set up in a 'quiet' area, shielded from Earthly broadcasts, then the far side sounds like a good bet. One problem would be, it wouldn't be able to transmit its data direct to us Earthlings: it'd need relay satellites. Servicing and repair of such an installation would be expensive! It costs a lot more to send astronauts to the Moon than just to put them in orbit.
  3. Very impressive. I take it the dark 'bands' are actually the shadow cast by the rings - something we don't see so prominently from Earth because we can't see Saturn at such an oblique angle relative to the Sun.
  4. True, but centring the secondary in the focuser is less critical than getting its tilt right.I meant collimate with the focuser pointing up, not the OTA itself! Unless you're very clumsy you're not likely to drop anything through the focuser tube onto the secondary! The question of focuser flex is certainly a good point, but difficult to allow and compensate for unless you always use the 'scope in the same orientation, with the same eyepiece. Probably best to collimate with the focuser unflexed. And the one thing that's really difficult (I've never tried, myself), is checking whether the focuser is square-on to the tube. I believe a Cheshire will show up that sort of error, but it's often difficult to correct - depends on the mounting of the focuser.
  5. To be honest, if you have not had practice with collimation, a laser collimator is easier to use than a cheshire - although not quite so accurate. Some may disagree, but I would certainly advise you to invest in one - they are not too expensive and you will find it useful to have alongside the cheshire. One snag is that the primary mirror has to be centre-spotted - or to be more accurate, it has to have a small paper ring (like those used for reinforcing pages in a ring binder) stuck to the exact centre. If your 'scope does not already have this, you will have to remove the mirror cell from the tube and do it yourself - it is not difficult but I can understand how some people may be nervous about this - I was! But you only have to do this once. Note that the ring won't affect your viewing in any way. The second snag is that the laser itself has to be collimated before you can use it. There are various guides as to how to do this. The point about using a laser is that you can 'see what you are doing' whilst making the adjustment - especially when collimating the secondary (which you should do before the primary). You can twiddle the screws and watch the spot moving about on the mirror as you adjust: this makes it very easy to home in on the centre. Then, when you go to adjust the primary, if you have twisted the laser so that the cutaway portion faces towards you, you can similarly 'watch what you are doing'. But if you are a perfectionist, your Cheshire is better for that final fine tuning. Do the collimation with the 'scope exactly horizontal and with the focusser pointing upwards. Then you eliminate errors due to the flexing of the focusser itself.
  6. I've had something similar - I won't name names. I ordered a crayford focusser and it didn't fit my OTA, I asked to return it and got the perfectly courteous reply "because there's no fault with the item, and because it's supplied to us by a third party, we can't take it back" etc. etc. I didn't know anything about DSR's and don't remember whether I was within the 7 day limit (probably not). To do them credit, the suppliers did try to help out, they made a sort of home-made adaptor and sent it FOC, but when I saw what they'd sent I decided not to use it. I let the matter drop and kept the focusser, unused: I still have it in its box, wondering what to do with it. Whatever advice I get on here I'm not going to take it up with the suppliers again! 'Sleeping dogs lie' and all that....
  7. That's a nice picture you've got there, very 'atmospheric' (if you don't mind the pun). Shows how, on this sort of photo, a little cloud and haze enhances the character of the image. I saw nothing. The Sun emerged from the clouds at just about 6:00am, ten minutes after it was all over.
  8. Well, if this isn't [exasperation]10, I don't know what is! Clouds parted exactly ten minutes after last contact !!! Got a lovely projection of a completely unencumbered Sun's disk. Ah well, saw the 2004 one in its entirety, so I can't really grumble.
  9. I think I've got an 'old friend' for each season. Orion, of course. Leo to herald the spring, then the Summer Triangle, then the Square of Pegasus and the line of Andromeda to round off the year. But there are others. Sagittarius always being a pain to pick out from British latitudes, I always look forward to it on a summer trip to France (going next week ), where the old 'teapot' stands bright and clear of the horizon. And if I'm there earlier in the year, the familiar quadrilateral of Corvus, for some reason, is something I welcome each time it returns. Why that not-very-striking constellation, I wonder? Possibly because it plays host to the Antennae, one of the most challenging DSO targets for me - and I've had two goes at it...
  10. We don't have to wait for M31, to find out about close encounters between the Sun and other stars. Many of you will have heard of Gliese 710 (if not Google it. Must admit, I had to google to recall the number ) Come 1.4 million years - a whole lot sooner than Andromeda - it's scheduled to pass just over 1 LY from us, shine at 1st Magnitude (currently its mag 9.7) and likely to disrupt the Oort cloud (if it's there) wholesale. Lots of fun 'n' games 'n' cometary impacts expected!
  11. No need for the time machine: courtesy of the HST, we can see beautiful galaxy-galaxy collisions happening right now:http://apod.nasa.gov/apod/ap080224.html Actually, not 'right now' of course, 300 million years ago really. Perhaps we are looking through a vast 'time machine' after all. But one-way only!
  12. If only I'd known. Wasted all that time setting up! How did they contrive it, I wonder? Aha! I think I have it! Evidently NASA set up a 1000 TW black laser (probably sited in Area 51), and allowed the beam to slowly sweep across the Sun. The black wavefront precisely interfered with the light wavefront coming from the Sun, causing a dark spot to appear to drift across the Sun's disk.And they're going to do the same next Wednesday. Have I got that right?
  13. Yes, I think NASA have done their 'hard sums' and come up with an actual time-scale for this event: that's what makes it news.
  14. It'd be great to own one of those - but I think I'd have to upgrade my car too:
  15. M32 and M110 will probably have been completely absorbed into M31 by the time this grand event happens. Some people think M33 is gravitationally bound to M31 - they are only 750K LY apart, much closer than M31 is to us. If so, perhaps it's not that far out to call M33 a 'companion' of M31. We might be looking at a 3-galaxy crash....
  16. OK OK still some time to wait! Some nice mock-up pictures on the BBC website: http://www.bbc.co.uk/news/science-environment-18285583 I like the second picture down especially: the one showing how the galaxies might be tidally warped. I expect the naked-eye views won't be anything like as spectacular, but if Earth is still habitable and has 'intelligent' beings (unlikely!) on it, equipped with widefield cameras, the available subject-matter should be spectacular!
  17. At first I was terrified of touching anything: I assumed that if I were to touch one of the screws by so much as a hairs-breadth, I'd never be able to straighten it out again! Once I'd taken the plunge and disassembled it in order to centre-spot the primary, and bought myself a laser, I grew a bit bolder. Now I find, I don't need to collimate for every session, but after every few nights or so. I find that a combination of laser, for the secondary, and cheshire, for the primary, works best. Talking about what people find acceptable in collimation, I remember, in the early days, going round a shop and looking over a few dobs, I asked a casual question about 'how easy is it to collimate'? The chap gave me a quick demo, he got me to look down the focusser at one of the display models, and remarked "as you can see, that one's already pretty spot-on". Well, even with my inexpert eyes, and with no sight tube to assist, I could see that it was far from it. But I held my peace... Maybe Dob users are less stringent?
  18. But in any case, what is a "KHz"? It's a measure of frequency based on our very terrestrial second, which in turn is merely a subdivision of the time it takes our planet to rotate once. Hardly likely that our friendly ETs will inhabit a planet with exactly the same rotation period! So they won't have any understanding of the time period 'one second'. There have been some suggestions that transmissions should be based on the neutral hydrogen hyperfine transition frequency, 1420MHz (21cm), since that is a natural 'resonance' which occurs across the known Universe, and any alien civilisation with a knowledge of astronomy is bound to be listening to it. Assuming we broadcast a carrier at that frequency, we'd merely have to modulate it in such a manner as to convince our ET listeners that it really is ersatz, and not a natural phenomenon. Once they've latched on to that, anything goes...
  19. Well perhaps I picked a poor analogy. Certainly, you are right, there are scripts not yet deciphered: apart from the ones you mentioned, there are the famous examples such as the Indus valley script and the Minoan Linear A. But set against these are success stories like Linear B, the Mayan Hieroglyphs, the Futhark Runes.... or were these only 'success' stories because the underlying language was already known? I'm no expert. Anyway, if we're intentionally sending stuff for ET to decipher, as opposed to accidentally blatting out rubbish like reality shows, we need to give them as many clues as possible. Like using prime numbers when packaging up the transmissions, etc. etc. The point is, we don't want them to be flummoxed!
  20. I think that if aliens could actually pick up our signals, then with sufficient intelligence, assuming they have a means of recording the data, they'll try every means of decoding until they come up with something intelligible. After all, didn't a team of ordinary humans (without the aid of modern computers) successfully decrypt Enigma, without a clue (in the first instance) of what it was all about? If humans can pull that off, who knows what a super-intelligent ET will manage?But will they be able to pick up our signals in the first place? I suppose it all boils down to signal-to-noise ratio. It's been shown, from the Voyager and Pioneer signals, that interstellar space isn't a particularly noisy place. I suppose it may come to the point where the transmitted signal strength falls below the cosmic microwave background. Or some sort of zero-point quantum energy arising from empty space. Or - of course - how good the ET's receivers are...
  21. I think the cost of getting the payload down to luna firma is the biggest factor. And astronauts to set it up (assuming it can't be done entirely by robots). You would have the advantage of a 15-earth-day-long lunar night, and very low temperatures (good for IR). But the moon is still rotating - albeit 30 times slower than Earth - so you'd need a driven mount and guiding, just like on Earth. The moon's albedo would only be an issue if you were using the 'scope in the moon's daytime. It would have to be shielded from direct and reflected sunlight. The low gravity means that a large mirror would flex much less than on Earth, but it would still flex a bit - so adaptive optics might be a 'must'. Apart from all these caveats - go for it! So who's putting up a down payment???
  22. The ancient Arabs would have had consistently dark skies. Nowadays, in dark skies, for people with normal eyesight and wearing corrective glasses/contacts if necessary, Mizar/Alcor are easy enough to split. Perhaps, seeing as opticians and eye tests weren't around in those days, it was a way of weeding out the short-sighted? Certainly, without my glasses on, I'd have a tough job discerning the Plough, let alone Mizar/Alcor. Or perhaps they could have used Epsilon Lyrae as a slightly tougher one. Or possibly even Albireo? I can split Albireo in bins if the skies are really dark, but I haven't a prayer with naked eye. But possibly some people have?
  23. There is an obscure galaxy called the Canis Major Dwarf which is only about 25000 LY from the Solar System, but its existence is disputed. After that there's something called the Sagittarius Dwarf Elliptical, about 70000 LY from us and 50000 from the centre of the MW (and about to collide with it). Its only observable feature in amateur 'scopes is the globular M54 which forms part of the galaxy. But as Stephen says, if it's a big galaxy you want then you're looking at M31.
  24. Certainly the barn owl that used to entertain me on my nocturnal sessions in France has not been around for years - maybe it deserted its home in the church spire when they put in the floodlights. And there could well be fewer bats than there used to be. Interesting observation on the picture in the BBC link. Despite all the horrible LP, you can see stars in the sky: I can distinctly make out part of Sagittarius there - can anyone else? I wonder what city it is a picture of - evidently looking South.
  25. Gawd these are awful! Coats all round and taxis called! I was thinking of making just about any remark about the planet that orbits between Saturn and Neptune, but on second thoughts.... OK. Many years ago an astronomer was visiting a remote island to observe a total eclipse. Unfortunately, the day before the big event, he is captured by cannibals, who assure him that he will be cooked and eaten. He manages to exchange a few words with the village headman who speaks a little English. He asks him exactly when they mean to cook him. "Tomorrow, when the Sun is high in the sky," replies the headman. "Aha," thinks the astronomer. "Maybe I have a chance. If I can convince them that I am a mighty god who will make the Sun disappear...." But the headman is continuing: "....but in your case, because everyone's so excited about the eclipse, we've decided to wait until the day after tomorrow."
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