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Charles Kirk

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Everything posted by Charles Kirk

  1. Why not just wait 4 to 6 weeks by which time there is a high probability that the restrictions will have been removed.
  2. Great report. Thanks for posting. I think that you would have a chance of seeing the pulsar at the heart of the Crab Nebula with your 20 if you like a little challenge.
  3. Another interesting article here https://www.skyandtelescope.com/astronomy-news/observing-news/is-betelgeuse-approaching-a-crossroads/
  4. These are really interesting images. Thanks for posting.
  5. I don’t watch this stuff on principle, it encourages more of it.
  6. Take this line from the article quoted in the first post, you remove the hyperbole which now seems to be part of most of what is written online, that sentence would read something like this. Betelgeuse is a highly evolved red supergiant the type of star that could collapse and explode some time in the next 1 million years.
  7. The temperature and pressure in the core of a star is a result of gravity, which is proportional to the mass of the star. In a star like the sun, the pressure from Hydrogen fusion balances the force of gravity preventing further collapse and corresponding temperature increase. At a certain point the star will run out of a Hydrogen in the core, the Helium core will then star to collapse increasing the temperature and pressure until, if the star has sufficient mass, Helium Fusion starts.
  8. Given a long enough timescale all stars are variable.
  9. https://www.assa.org.au/resources/variable-stars/observing-variable-stars/ Experienced visual observers can see 0.1 mag differences under ideal conditions, and 0.2 mag more typically.
  10. To make comparisons between variable stars and comparison stars in the same field you would need to have 100% field illumination for the circle containing the two stars. For that reason you would want a larger central obstruction than you would in a reflector optimised for observing fine details on the planets and/or moon. Personally I would not be interested in purchasing a coma corrector that cost twice as much as the telescope that it was going to be used with. I would have thought that the difference between the two is more likely to be due to astigmatism.
  11. Firstly you need to observe after the end of Astronomical Twilight, you can find that by googling astronomical darkness, which will give you the latest date before the summer solstice and earliest date after it when you have Astronomical Darkness. To achieve the optimal view from the UK you would really need a sea horizon where you are facing south, which rules out north Cornwall and north Devon, that way you eliminate any light pollution. The Scilly Isles would be a great location.
  12. The production cost increases significantly when working to higher tolerances. That in combination with the additional optical elements in the baffle tube to correct for both coma and field curvature is the reason for the price difference. Also the margins tend to be higher on premium products. The white paper makes a good read, a skilfully executed technical sales document. For Visual some people are more sensitive to the coma in conventional SCT designs which makes the EdgeHD attractive. Another thing is that as interests evolve over time the EdgeHD is better futures proofed for an observer who starts out main interested in visual but becomes interested in imaging. The pricing in the UK is incredibly expensive compared to the US it looks as if Celestron want to preserve their profit margins in USD despite the fact that the telescopes are manufactured in China by Syntra.
  13. My first telescope, back in the 1980s, maybe around 1983/1984 was a Fullerscopes 8.75 inch 222mm f/7.25 on a Fullerscopes Mark III mount. It sound like this may be the same model. Quite an unusual mirror size. I have fond memories of that scope, superb views of star clusters and double stars.
  14. The result will be a Supernova Remnant rather than a planetary nebula, there are some important differences http://www.astronomy.com/magazine/ask-astro/2013/08/planetary-nebulae-and-supernova-remnants
  15. Just to make the Aperture Fever a bit worse http://www.reginato.it/telescopes.htm 24inch heaviest part 26Kg. Italian engineering flare.
  16. We only have accurate brightness estimates for around 100 years, a very short period compared to the 100,000 year timespan in which it is anticipated that Betelgeuse may become a Supernova. I do think that it would be quite profound to see both the Sun and a Supernova in the sky at the same time.
  17. Well that's disappointing to hear. On the other hand, it's very good to hear that the mirror is good, as the rust and other minor issues I have read about would be solvable. They do seem to have been quite well received in the comments I have read.
  18. It seems highly unlikely that the optics would be made as a matched optical set, it would be far too expensive, it’s more a question of the mechanicals, how they are fitted into a tube and aligned. In particular, the corrector needs to be squared up to the primary. Of course if you were marketing/selling them you might describe that as a matched optical set. The corrector plates are made on a metal mold to produce the complex shape. Tom Johnson who founded Celestron invented the process which allowed the inexpensive mass production of the corrector plates and, as the two mirrors are spherical the inexpensive mass production of SCTs. The purpose of the coatings is to lower the reflectivity of the corrector plate the same process is used for eyepieces.
  19. Was that a first generation model or a second generation model?
  20. I think that the corrector plate are custom fitted at the factory in terms of their alignment both with respect to the position of the secondary and the tube, so even if you could find one it would be a non trivial task to align it.
  21. Am I correct in assuming that the spot analysis is for the edge of a 2.0 inch (50mm) field for 20 inch RC and CC apertures? The analysis is very interesting and probably explains why they went for the CC design at f/12 instead of an f/12 RC design, the CC design being slightly easier to build. I don't understand the effective aperture discussion in the CN review https://www.cloudynights.com/articles/cat/user-reviews/telescopes/gso-8-inch-true-cassegrain-r3215 Using a smaller secondary will increase the contrast of fine planetary detail and reduce the fully illuminated field diameter which the review states is 100% over a 15mm diamater, but the effective aperture is going to be similar to that of a Celestron 8 Edge as they both have central obstructions of similar size. I wonder if the lower image brightness in the CC was one or both of higher magnification and a smaller fully illuminated field diameter .
  22. I think that all Skywatcher mirrors are parabolic 1/4pv (diffraction limited). The Skywatcher Explorer 130M looks to be the best choice out of those. I would not purchase from Amazon, much better to support a small company that specialises in telescopes like FLO.
  23. Good animation, it really brings home how much dimmer it is. I saw it on Friday evening, it was around the brightness of Bellatrix. The following article has some long term light curves. https://www.skyandtelescope.com/observing/fainting-betelgeuse/
  24. Those upgrades look very useful, so I think it depends on whether you have the time and inclination to make those types of modifications yourself or prefer to pay more to have something that works well out of the box. The flocking would be time consuming to do, so the labour cost would account for some of the price difference.
  25. I wonder why they didn’t make an f/12 RC instead, which would be have a smaller central obstruction than the current f/8 models. I suspect that they wanted clearer product differentiation and saw a market for the classical Cassegrain design. No corrector plate to dew up saving the cost of a dew shield is certainly attractive.
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