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About Xilman

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  • Interests
    Almost everything scientific & technical. See web site for astronomical interests.
  • Location
    50% Cambridge, UK 50% El Paso, La Palma
  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
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