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Xilman

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Everything posted by Xilman

  1. 8 millimags is a very close value. It is extremely difficult to discover, measure and account for differences at the 0.1% level. The formal precision estimated from SNR considerations may be that low but systematic errors are a different kettle of fish.
  2. True for visual observers. I aim for between 0.01 and 0.03 most of the time, rising to 0.1 below magnitude 18 or so, and 0.001 to 0.003 for exoplanet transits. I use a CCD camera for those.
  3. "What am I doing wrong?" --- you are multiplying and not taking logarithms. To a very good approximation, and for fairly small values of x, a difference of x millimags corresponds to a 0.x% difference in brightness. So 8 millimags is about a 0.8% difference. 0.74% is indeed about 0.8%. For those who did A-level mathematics, consider the power series approximation to ln(1+x).
  4. If you want a historical example, look at William Herschel. He built a 48-inch reflector and used it to discover Enceladus and Mimas. Otherwise, it was an embarrassing failure and not a patch on his 18.7-inch which he used to make thousands of discoveries. The satellites would have been easily visible in the smaller telescope if he had used it at the correct time, which is when Saturn's rings were edge-on.
  5. We are going to have to disagree on that one. What is important is not how big it is but what you do with it. Many people have discovered that it can be much harder to use a large scope than a small one and so end up rarely using it. Other people make frequent and good use of a manageable telescope or pair of binoculars. I know one guy who does impressive astrophotography armed only with a smart phone and somewhere stable to rest it.
  6. Impressive! I have a 10" Dob but I doubt very much that I will be able to come close to matching your achievement.
  7. Bahtinov mask http://aladin.u-strasbg.fr/AladinLite/ https://minorplanetcenter.net//iau/mpc.html
  8. Ah. My responses were also concerned with observing. Many (most?) astronomers think of the term "observing" as "collecting new information on astronomical phenomena", which can be broken down into two categories, one of which is "visual observing" and the other is "instrumental observing". The latter is further broken down into imaging, spectroscopy, astrometry, photometry, and so on. Radio astronomers make observations but they certainly don't use their eyeballs as the detectors of incoming radio photons! You clearly meant to write "visual observing".
  9. This is a wonderful example tweeted today: https://twitter.com/PeterLewis55/status/1329375163218087937/photo/1 It contains all of Orion and Lepus, Taurus as far as the Pleiades, Canis Major as far as Sirius, and chunks of Eridanus and Auriga. It is possible to measure stars down to at least sixth magnitude. In particular the brightness of Betelgeuse can be estimated by comparison with Aldebaran. It clearly needs some flats taking, but that is a detail. Image taken from light polluted London.
  10. Exactly. They are widely separated and the secondary would be an easy binocular object if it wasn't so close to the primary. Clean optics, acute vision and good seeing are essential to see the Pup in a small telescope. Or a big one, for that matter. Much like seeing Galilean satellites with the naked eye, in other words. Possible, but very much not trivial
  11. I first came across and used Hinds equipment 1975 whe I was a student. A very nice 8" reflector.
  12. Pretty much the same for me, but the 98% solar eclipse back in 1999 was impressive. I saw the scars from SL-9 during a conference held in Boston. A friend at MIT invited me around to a meeting of their astronomical society where they had set up a telescope on the roof of a faculty building in Cambridge.
  13. I very much doubt that sensors will be exclusively OSC. Professional astronomers will absolutely require that their observations be reconcilable with the standard Johnson-Cousins UBVRI... the Sloan ugriz ..., or Strömgren ubv ... pass bands and will not stand for the loss of sensitivity consequent on splitting the incoming photons over multiple detector sites. You may have to pay more to be able to play with the big boys.
  14. As has been observed many times before in many contexts, it is not the size that is important, it is how you use it. Hence my slightly tongue-in-cheek (only very, very slightly) post about a 2.2mm aperture refractor. On Twitter I have seen images of the likes of Ceres taken with nothing but a smart phone and a solid place on which to rest it. One can do photometry of genuine scientific importance with a sub-5mm aperture refractor. Many variable stars reach magnitude brighter than 7.5 and a wide enough field of view is unobtainable with more conventional telescopes where comparison stars can be hard to find.
  15. Greetings from soggy, by Canary Islands standards, that is, La Palma. I can confidently state that I have never seen condensation inside the dome. The scope is fitted with a dew heater but it has not been used in years, if ever. Rain, OTOH, can be ... err ... interesting. We sometimes get several centimetres in the course of an hour or two. Paul
  16. An image taken with a 2.2mm f/1.8 refractor appears at https://britastro.org/node/20154
  17. This is getting really far off-topic ...
  18. Indeed species and environment evolve together. However, the vast majority of species reproduce asexually, not just a few. Think bacteria, amoebae and yeasts for a start. Garlic, although technically a flowering plant, hardly ever flowers, let alone produce viable seed. If you want an animal example, try tapeworms.
  19. Read up on bacteriophages, viruses which infect single-celled organisms. Read up on transposable elements and selfish genetic elements which are parasitic on DNA, something which is but only a tiny component of an amoeba. https://en.wikipedia.org/wiki/Transposable_element and https://en.wikipedia.org/wiki/Selfish_genetic_element are good starting points.
  20. Given that very few species last more than a few million years, you are almost certainly correct in your belief. If we hang on for another century or so, AIs may well prove to have a longer lifetime than primates.
  21. Current observations suggest otherwise. The universe appears to be expanding ever faster (look up "dark energy" or "cosmological constant") rather than slowing down ahead of a big crunch. What *might* happen is a quantum fluctuation temporarily creates enough energy in a small enough volume of space-time for a new inflationary epoch to occur. A good search term is "eternal inflation", and specifically "bubble nucleation" as used within that context.
  22. No-one yet knows. IF: Expansion continues indefinitely; Black holes evaporate into radiation through the Hawking process; Protons decay, if only because their constituent quarks very, very occasionally approach each other closely enough to lie within their gravitational event horizon and collapse into a proton-mass black hole THEN the universe ends up made up of ever more red-shifted photons, neutrinos and electron-positron pairs which are too far apart to mutually annihilate before cosmic expansion drags them even further apart. Each pair forms an atom of positronium parsecs in diameter. Our current knowledge of physics is so pitifully crude that this is at best a plausible guess.
  23. Unfortunately people won't be living on Earth in 4-5 billion years unless we do something to prevent it (a) becoming uninhabitable for life as we know it in about 1-2 billion years through increased solar luminosity and (b) being swallowed up by a red-giant Sun in the 4-5 billion year time scale.
  24. Although very few stars will collide directly, the ISM (gas and dust) surely will. It will set off a burst of star formation. We can see this happening in other galaxies. As you note, the galaxies (treated as units, not their individual stars), will merge after the collision. Both sound like a reasonable description of "crash" to me.
  25. Personally I would RMA it. Fiddling around with it and failing to make a successful repair gives the supplier an excuse to void the warranty.
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