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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. Xilman

    15-30cm Dobsonian

    My observatory is in La Palma which is in lock down for the foreseeable future. It would be nice to be able to do some observing from the admittedly cruddy skies just south of Cambridge where I can't sensibly house a permanently mounted telescope. As a VS observer I'm interested much more in light grasp than exquisite definition and sub-arcsec guiding. Consequently, I'm looking for a Dobsonian in the 15-30cm aperture range and preferably towards the larger end of the range. That's six to twelve inches for those who think in those units.
  2. Now that Windows7 is officially moribund I want to move the TCS to Linux. EKOS works nicely with the LS200 look-alike mount and SX gear. At least it drives the cameras properly, not yet tried with filter wheel and AO unit. That leaves the dome and the focuser to be sorted. The latter is called a LazyFocus on the Windoiws box but it seems that it is the same as the Moonlight focuser in the INDI world so that is next on the list to be tried. So far, so good, but I am having real trouble discovering how to drive the dome. At present Windows is using LesveDome with the Velleman K8055N ASCOM driver. Despite rummaging around on the interweb thingy I have yet to find a Velleman INDI driver. Can any one help? TIA, Paul
  3. At long last I have managed to image Caliban, also known as Uranus XVI. It is a small (circa 72km) outer satellite of Uranus which was discovered in September 1997 using the Hale 5m telescope at Palomar. Incidentally, Sycorax (U-XVII)was discovered in the same observing session. That satellite is around 1.7 magnitude brighter and so much easier to observe. Although a three hours exposure, unfiltered for maximum sensitivity, was used the signal to noise ratio is barely 3 and serious image processing was needed to produce a relatively clear image. Even so, it is not especially obvious. The reason is that the MPOC ephemeris predicts that the satellite has a magnitude of 22.2 at the time of observation. More information is available at http://www.astropalma.com/Projects/Satellites/caliban.html
  4. You don't have a hope in hell of seeing Proteus. It is far too close to the planet and will be lost in the glare. Even if it were far enough away, picking up something below 21st magnitude will not be easy. Others have commented on the visibility of Triton. If you have a decent camera, good guiding and sufficient patience Nereid is possible, though not entirely trivial. It is quite faint, at mag 19.5 or so, and is in a wide orbit so you will need a good ephemeris as it may not be in the same FOV as Neptune. https://minorplanetcenter.net/iau/NatSats/NaturalSatellites.html is the place to go. Here is my image of Neptune, Triton and Nereid. The main image is a 400s exposure and Nereid is circled. The inset is of 3 seconds; unfortunately Neptune and Triton are over exposed. I must try to get a better one some time.
  5. Depends also on whether you want to do accurate photometry. If so, take a dark just before (or after) each science shot to be certain that the temperature has not changed significantly. If the temperature is fairly constant over a significant period the darks can be taken less often.
  6. I really don't know where to post this one as it covers cameras, telescopes, mounts and software. If it should not be here, doubtless a mod will tell me where to go. Background information: a bunch of telescopes are all on the same equatorial fork mount which is controlled by a Astro Electronic FS2 device. The FS2 is a LX200 emulator. The main scope has Starlight Xpress kit plugged into it, specifically an AO unit, a filter wheel with OAG capability and a SX-814 camera. For reasons which are not immediately relevant a Lodestar2 camera doesn't work with the filter wheel. Accordingly, it is attached to a subsidiary refractor. A standard SX-supplied cable connects the Lodestar to the FS22. All this stuff, and more besides, is driven by MaximDL v6 under Windows 7. The FS2 is driven through a serial cable just nicely for pointing the mount in the right direction so it clearly works to a very large extent. Despite extensive experimentation I have been quite unable to configure the system to use the Lodestar as an autoguider. MaximDL controls it just fine in that perfectly good images can be taken if "Camera 2" is selected. "Camera 1, of course, is the main SX-814; it also takes fully usable though unguided images. In practice they are limited to around 30 to 60 seconds each. Both cameras and the filter wheel appear as USB devices. I have yet to persuade MaximDL to control the FW but that is a very minor problem given that the Starlight Xpress app works very well and is simple to use. My guess is that subtle and arcane incantations are required before MaximDL will do The Right Thing. Does anyone have any suggestions as to what they might be? Thanks, Paul
  7. My personal view: extraterrestial live is virtually certain to exist. There are several reasons why I believe it to be so. First, in our neighbourhood we already detecting an average of one planet per star --- Kepler has shown that. There are roughly 1e12 stars in our galaxy and roughly 1e13 galaxies in the observable universe. The MW is bigger than average, so let's be conservative and estimate around 1e24 planets. That is a big number. However that applies only to planet-based life. Chuck in moons and the number of habitats could be several times larger. We can reasonably expect 1e25 solid bodies in orbit around stars. Second, there are several places in our solar system where earth-like life could have evolved. By that I mean carbon-based using liquid water as a solvent. Planets include Venus & Mars and the atmospheres of Jupiter, Saturn, Uranus and Neptune. Bacterial life could well have survived high up in the atmosphere of Venus and underground on Mars. Both planets were really rather friendly earlier in their histories. The gas and ice-giant atmospheres have very large volumes where the pressure and temperature is close to that which terrestrial life finds comfortable. There is a great deal of evidence for sub-surface oceans in several of their satellites. Third there is some evidence and several plausible lines of argument to suggest that water is not required for life. There is some truly fascinating chemistry going on in low-temperature non-aqueous solvents, with analogues of sugars and lipids having already been synthesized. Searching on the term "azotosome" may lead you into some interesting chemistry which should be possible in the liquid methane seas on Titan. "Polysilanol" is another good word, https://www.semanticscholar.org/paper/Many-chemistries-could-be-used-to-build-living-Bains/321cabdb19e7debb78613ef38b925475b9f4580d is a specific reference. Note that I have not yet brought in any wilder speculations such as Black Clouds, black hole Eaters and Cheelas. Fourth, and really rather important in my view, our experience is that it didn't take long for life to evolve on the earth (with relevance to the Mars and Venus comment above) and once it took hold it proved to be ineradicable. It sailed through several snowball earth episodes, for instance. On a shorter term, viable viruses were returned to Earth after spending a couple of years on a Surveyor probe exposed to the lunar environment. It will interesting to see whether of those infamous tardigrades survived their journey. Extensive modelling and a few experiments with hypervelocity projectile guns have shown that viable bacteria can be chipped off the terrestrial planets and survive long enough to land safely on a different on. Perhaps this may not be a proof in the mathematical sense but it surely reaches the "balance of probability" criterion in civil law suits and, in my opinion, beyond all reasonable doubt in criminal cases.
  8. Not entirely sure I understand all of the above. Possibly it's because we may be addressing different problems, the clue being that you keep mentioning the use of the guider star images. My starting point is that I have an image and wish to "improve" it using only the information held within that image. Improvement generally means increasing the resolution of the without damaging its astrometrical or photometrical properties "too much" --- a rather subjective criterion. My implementation of CLEAN is still very simple and follows the original Hogbaum formulation. It can be improved greatly in at least two ways. The PSF estimation is very poor, being essentially a weighted sum of image patches centered on a few bright stars. Although that has the benefit that the PSF need not be anything like a Gaussian or Moffat profile (jaggies from poor guiding for instance), it has the disadvantage of having pixel resolution at best for each star which itself means that the composite PSF is broader than it should be. The other is that rather than fitting a PSF properly to each source in the dirty map and subtracting, I just centre the PSF at the brightest pixel at each iteration. Again, this does not give sub-pixel matching but, more important, is too sensitive to noise in the dirty map. Dark subtraction removes truly hot pixels but a cosmic ray hit or satellite trails gives a nasty artefact in the final image. So far, removal of bright non-stellar objects has not yet been implemented Even that crude an implementation shows promise on unresolved double stars.
  9. This thread is fascinating! I´m a newbie at SGL and now wish I´d come across it previously. Just a couple of comments for now. 1) I find that the CLEAN algorithm can work rather well on stars. See https://britastro.org/node/19566 for an early blundering in this area. 2) Co-adding stellar PSFs to reduce noise is a long-used technique. The observed PSF is generally best represented as an elliptical Gaussian or Moffat profile together with a discrepancy bitmap. This approach is used in the DAOPHOT software for crowded field photometry. DAOPHOT can be found in the NOAO package within IRAF or PyRAF which is how I use it. I have not tried to find alternative implementations. Looking forward to seeing your source code.
  10. That is why VirtualBox or VMWare are so very useful things to have installed on your machine. You can still run MSDOG or OS/2 if you so wish.
  11. You have just described, accurately and succinctly, the difference between viewing and observing.
  12. Old fogies like myself just use a traditional paper atlas. Uranus is so bright that anything which goes fainter than good old Norton's is fine. There are many on the market, both new and 2nd-hand. If you see a brightish star which is not on the atlas it is Uranus or, just possibly, Vesta. Their colours are quite different. Neptune is a bit trickier in that relatively few traditional atlases go to 8th magnitude or below. Uranometria 2000 is a notable example. A few more asteroids become this bright; Ceres (not technically an asteroid these days, but I'm an old fogey) and Flora are examples. The colour is still a dead giveaway. And, of course, the BAA print custom charts every year. I'd recommend joining but you don't have to be a member to purchase their annual Handbook which contains a large amount of useful information for the visual observer. The 2020 issue tells you that Neptune reaches mag 7.8, Ceres 7.7 and Flora 8.2 --- there is no chance of confusion because they are in completely different parts of the sky.
  13. Could you install stock 32-bit Ubuntu and then apt-get the packages which bring it up to (enough of) a clone of Astro Ubuntu? A PITA but rather similar to what I've been doing on my Ubuntu 19.04 system. However, you do get the chance of running a light-weight window manager.
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