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JRWASTRO

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About JRWASTRO

  • Rank
    Star Forming

Profile Information

  • Gender
    Male
  • Interests
    Astronomical Sciences. Image processing.
  • Location
    South Australia
  1. Re: send commands to my mount via Matlab without passing trough a Synscan controller but I'm not sure if it is do-able. Brave man! You can do anything with MATLAB and Simulink ( https://au.mathworks.com/products/simulink.html ) How much cash have you got ? These mathworks chaps charge like a "wounded bull" ! Have you seen the open source approximation to MATLAB called OCTAVE ? Jeremy.
  2. I have a 10" dob like the one you have and place a 20 Ah battery as close to the centre as is possible. The OTA just misses the battery. As they say " a miss is as good as a mile". This arrangement works well but I am looking for a "cheap" lithium battery of 20Ah but, so far, I have been unsuccessful. Hope this helps. Jeremy.
  3. Greetings Brodie, Re: B " In space, the angular resolution of the Keck telescope is govererned by the diffraction limit. " Really ? Where did you read this ? About diffraction limited optics, These books have definitions of what it means when an optic is diffraction limited: 1. Introduction to Fourier Optics by Joseph W. Goodman See p. 129 " An imaging system is said to be diffraction limited if ..... " 2. Aberration Theory Made Simple. (SPIE PRESS Tutorial Text) by Virendra N. Mahajan See p. 79 " The aberration-free image of an object is also called its diffraction-limited image .... " 3. Basic Optics for the Astronomical Sciences (SPIE PRESS) James B. Breckinridge P. 227 10.2.2 High-angular-resolution astronomy: stelar diameters. BTW : Nice picture of the Keck Telescopes on the front cover. 4. Diffraction, Fourier Optics and Imaging Oran K. Ersoy p.142 " An optical system is diffraction limited if ... " Ersoy, here, refers to Goodman (ref # 1 above). I have other books but the above references will help you answer your question. Jeremy
  4. nil desperandum . This is the cure all in two parts :- 1. According to Douglas Adams, I quote " 85% of all known worlds in the Galaxy, be they primitive or highly advanced, have invented a drink called jynnan tonnyx, or gee-N'N-T'N-ix, or jinond-o-nicks, or any one of a thousand or more variations on the same phonetic theme. The drinks themselves are not the same, and vary between the Sivolvian 'chinanto/mnigs' which is ordinary water served at slightly above room temperature, and the Gagrakackan 'tzjin-anthony-ks' which kill cows at a hundred paces " 2. https://www.craftginclub.co.uk/join-freeginspecial?om_campaign=omme_de8a9efc-b34_1816_3101&om_send=72c0b67ce098420495697aefbc72fcf8&utm_campaign=omme_de8a9efc-b34_non_members_free_gin_170519&utm_content=freegin170519&utm_medium=email&utm_source=ometria Jeremy.
  5. Two points:- Point 1. OK with equation 78 when A and B are the sides of a right angle triangle. B is the hypotenuse. If A/B --> 0 then the angle theta tends to 90 degrees. Cos(90) = 0 and Sin(90) = 1 (angle in degrees) Seems to be a mix-up here, perhaps what was meant:- Lim ((sin(a)) ) / a --> 1 a --> 0 It is written like this because as the angle a=0, sin(a) = 0 and the division 0/0 is meaningless. When the angle is tends to 0 radians then a = sin(a). If A/B = sin(a) when a --> 0 then we can say the angle a in radians is a = A/B Point 2. One does not need to go through the above reasoning if one uses the definition that on a circle (radius r) the length of the arc (S) is S = r * a where a is the subtended angle at the centre of the circle. For very small angles the arc and chord may be taken to be of the same length. Distance to the star may be calculated from: r = S/a. Angle a may be measured by the large land based telescopes. I see no problems here. Re: You can measure the position of the star ie the centroid of the star image to much greater precision than the resolution. Yes of course. Good point. Jeremy
  6. Greetings Observers, Here is a link telling us about Jupiter being in opposition. It will be very bright and large : https://in-the-sky.org/news.php?id=20190610_12_100 Hope the weather is excellent on the 10-June-19. Jeremy.
  7. Re: is the optimal sub-length for a particular telescope, camera and SQM combination ... all condensed from this article. That said, there are some on here who disagree with the specifics. For a bit of discussion, see this thread. Wonderful. I will read "this article" slowly and in detail. Why? Because Quote: σe=newhere ne is the number of electrons collected by the pixel and σe is the standard deviation of the number of electrons expected between pixels all exposed to the same light intensity. End quote. Here he alludes to Poisson distribution. This article deserves reading. Thanks. Jeremy Addition: Just read the article and it is excellent. Beautifully explained. I have taken note! JRW
  8. Re: Scope handles are a very useful feature usually omitted by the manufacturers on budget scope designs. So True, Geoff. One of my telescopes has a built in handle. The finder 'scope doubles as a carry handle and is placed so that there is almost "prefect balance : Re: Hmm perhaps one of these could be adapted. Looks like a pretty, if not expensive, engine crane. I have one of these in my shed but it is all manual. Jeremy.
  9. Re: " But it doesn't rhyme. " OK. But you've got to admit my attempt is not too bad. Alright I've taken the bait. What are those formulae, in your signature, all about? Jeremy.
  10. RE: ... Shouldn't that be sine theta over sine phi - angle of incidence and angle of refraction? I think theta has a nice ring to it. Poetic licence allowed us to remove the subscripts!! Naming angles? Take your pick. The two angles may be (theta1 and theta2) or (theta_i and theta_r) or (phi1 and phi2) For me Theta and phi have always been associated with angles eg. polar co-ordinates ... (r,theta, phi). A sine wave: sin(omega * t +phi) , we could write theta = (omega * t + phi) . How's That ? Jeremy.
  11. There was a caveman named Snell He was really the spear fisherman from hell He could tell by the bend of the spears end It was sine theta over sine theta well, well ! My best attempt at doggerel, Jeremy.
  12. JRWASTRO

    Saturn

    Greetings Readers, I had to do some research for my bi-monthly talk/lecture series. This talk has a discussion of the planet Saturn under the aegis "Planet of the Day". OK. Here is a reference that will be of interest on Saturn's Disappearing Rings : https://solarsystem.nasa.gov/news/794/nasa-research-reveals-saturn-is-losing-its-rings-at-worst-case-scenario-rate/ And if you are really keen on Saturn here is a link to download an excellent book: https://solarsystem.nasa.gov/resources/17777/the-saturn-system-through-the-eyes-of-cassini-e-book/ Good reading, Jeremy
  13. Hello G4EQZ, With a name like that you should be well used to constructing your own stuff !! 1. Re: " Its a pain dragging the scope out into the garden and setting it up every time " I have this problem. I am in the process of finding a way to setup quickly and accurately. I will be posting my effort in the DIY astronomer section. 2. Re: "A pier where the mount can be setup permanently ... " A pier is excellent BUT commonly available mounts, like mine, are not exactly weather proof. I would be averse to keeping these things outside (even if they are covered) as they are not designed to be subjected to the "huge" changes in temperature and humidity. In my case the temperature range is from 47C to -5C. Dew point from 6 to 9C to -5C (condensing atmosphere ). Remember, most of the time these mounts are not used. We need Mil Spec stuff !! 3. Re: Piers. They are made out of all sought of materials and sizes. What advice can I offer ? Think of a shaft that delivers power and consider the materials used in making these shafts. These materials will be eminently suitable, in pipe form, with which to make a pier. If you have a mate in the refrigeration business then a short length of "Ammonia Pipe" will be a good choice. 4. Re: " though I gather wedges are a PITA to setup ... " Not Really. A little bit of practice will fix all !! 73's Jeremy.
  14. Re: Joining those concrete blocks. 1. Use large good fitting washers on each side of the joining screw. 2. At the join between the blocks you may make a paste made of floor leveling compound. This paste will serve as a gasket. The floor leveling compound is a very high strength ( 18MPa ) cement and will also serve to anchor the screws in place. Jeremy.
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