JRWASTRO

Typical Vixen. Excellent quality. Jeremy.

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

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.

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.

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.

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.

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

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.

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.

Interesting picture. Judging by " ... over the last five years it developed these ... " Sounds like a dirt/dust problem. 1. Diffraction patterns should be symmetrical so that "little spike" presents a problem. Notice that the star has multiple diffraction patterns - there is an aperture and flare issue here. ** Do you see the same patterns in an eyepiece ? If not then the camera sensor may need cleaning. ** Check the cleanliness of the primary and secondary mirrors. Jeremy.

Greetings Mark, You have chosen quite a colourful object to photograph. The approx size of Rho Oph region is about 4.5 x 6.5 degrees. Now with your 135mm lens and a APS-C sensor of 14.8mm x 22.2mm (Canon cmos sensor) you will get a field of view of 6.3 x 9.4 degrees. An excellent match. Jeremy

Yes, The book by Jean Meeus is excellent. I have coded a number of the algorithms, in that book, to run on my " HP Prime " calculator. The algorithms are being trialed for celestial navigation and are very very accurate. One would be most useful for users of Sun Dials. If anybody has one of these calculators and would like to try out this code they are very welcome to it. I can place it in this post. Here is a screen shot of the Analemma /EoT Plot on the HP Prime Calculator:- Jeremy.

Greetings Paul, Re: " Standing beneath blazing streetlights, the council recently replaced the old sodium lights with LEDs, " Common problem everywhere. Those LED lights ? Well, sadly, these are broad spectrum lights and none of our common narrow band LP filters will work. Can you not bundle your astronomical stuff into your car and take a drive to the country for a night of observing ? When my neighbor and I want to do some observing and some not so serious photography we have to drive about 265 km from the city of Adelaide ( I do not live in Adelaide) to get almost no light pollution but, to get truly dark skies we have to move an extra 300 km to the north !! More than 265km implies a family outing of more than a day !! Jeremy.

Greetings Readers, https://www.e-booksdirectory.com/details.php?ebook=3483 For those who are interested in the mathematical astronomy: Elementary Mathematical Astronomy by C. Barlow, G. Bryan And Practical Astronomy by P. S. Michie, F. S. Harlow - John Wiley & Sons Are excellent. The mathematics is the same as now!! Contrast this with the "Ultra Modern" : Gravitational Waves: Sources, Detectors and Searches by Keith Riles - arXiv and for the very brave: Astronomical Image and Data Analysis by J.-L. Starck, F. Murtagh - Springer I have not looked at the last reference as it costs money. Horrible. Good reading for our winter. Jeremy.

Point 1. Point 1) As I use the term a 'stack' is the output from the combination of a set of sub exposures using one of a number of algorithms. So stacks of the same set of subs may vary depending on the algorithm chosen. We need to know what the particular algorithm does and the idea behind the procedure. Once we know this then we may take steps to answering the question as to whether there is gain to be made by "stacking" already stacked images. Possibly if there is some non-linearity like clipping or limiting is involved then things might get worse. Point 2. " simple averaging of pixel values " is the best strategy for estimating a signal in the presence of gaussian noise. It appears to be simple but the basis is very sound. It is impossible to separate signal from noise the best we may do is find the the best estimate of the signal in the presence of noise. The expected value of the noise is zero (0) so when we average the signal (signal + noise) the SNR after averaging is higher (the noise power (variance) is reduced). About good and bad subs: Question : What is a determinant of the quality of an image frame ? We need to quantify this quality. SNR is a start. Is quality determined after we have removed as much of the systematic errors (Signal to Interference Ratio) as we can and look at the noise gradients in the image? I do not know. Jeremy

I, once upon a time, estimated the power of those super fit chaps who run from the bottom to the top floor of the Empire State Building ... 420W max ... model aeroplane engine class. Weak. Jeremy.

Fully agree Jim. I think we are hard pressed to output more than 200W (two light globes worth). Depressing. Isn't it? Jeremy.

Re: Is a stack of stacks the same as doing a longer stack? My 2 bob's worth follows:- Before one can answer this question one needs to develop a model of this system. 1. What does "stack" mean ? If anyone can answer this question we may proceed from here. If there is any form of non-linearity in this system (clipping etc.) then "hello Houston, we have a problem" . 2. If we make the grand assumption, that AFTER we have collected the original signal, the only noise in the system is white gaussian noise (WGN) we may say that the stack of stacks (average of averages) is the same as stacking all the individual images. We really need to know what the designer of the program has in mind and what is the science behind his/hers code. Perhaps if one is continually adding images to be "stacked" then I would suggest we use an exponential average as ti has a "forgetting factor". Jeremy

Firstly - my sincere apologies for the late reply - we had to take a sought of quick drive to the Gold Coast (near Brisbane) to see our new grand daughter. I'm back now ! Invoices like that ? Yes. Someone took the trouble to write it up! The condition of the mirror is "not too bad" but the effort required to make an an excellent 'scope is large so I am still pondering. Jeremy.

In appreciation of a series of talks (34 hours and continuing !!) on astronomy I was given this mirror. It is an old mirror and may need re-coating. For nostalgic purposes I might just make a telescope using this mirror. Here: Jeremy.

We also have an observatory !! From Jeremy.