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Rasa is very poor choice for small targets as it is very short focal length and far away from diffraction limited optics.

Maybe best way to approach it would be to set your working resolution first? ZWO 6200 has small pixels at 3.76um, and odds are that you'll have to bin that camera extensively with long focal length instrument. Say you opt to go with 1.2"/px, Your base focal length is 646mm This means you need to go in increments of that: Bin2 1292mm Bin3 1938mm Bin4 2584mm C925 with reducer is smack in the middle of that with 1645 - neither here nor there. Why don't you just go with 9.25 Edge HD without reducer? That is better option. With Bin x4 it will give you 1.32"/px and if you are feeling lucky - x3 will give you 1"/px (you do have mesu after all). If you are tempted to get reducer to speed up things - don't. Best way to speed up things is to find your wanted working resolution / sampling rate - like say 1.2"/px and then throw as much aperture as you can that will be well corrected for 43mm and will fit in your obsy. I'd rather use something in 12" RC - 16" RC range than 9.25". Maybe look at CCF and Officina Stellare scopes since money is not issue - these seems to be better built with less issues than GSO RC scopes. https://www.teleskop-express.de/shop/product_info.php/info/p13582_TS-Optics-RC12-Pro-304-mm-f-8-Ritchey-Chretien-Telescope---Mechanics-by-CFF.html In any case - 12" RC will have 2400mm of focal length - so same as Edge HD 9.25 - so same sampling rates for bin factors - but it gathers x1.7 more light. Another option would be for example this scope: https://www.orionoptics.co.uk/product/odk14/ 2380mm of focal length and 14" of aperture. Seems to be well corrected for 52mm diagonal. Remember - you'll be using 4 x 3.76 = 15um effective pixel size - so these spot diagrams are even smaller compared to pixel size then the image suggests.

While technically correct - it is not complete picture and can lead to misconceptions. There is indeed 4-vector and it "rotates" (not quite the same as 4d euclidean that we could use sphere and unitary vector pointing in some direction) to align with certain directions / axis, but this line of thinking sort of implies that space-time of the background is "fixed" - much like fixed coordinate system - but it is not - every reference frame has it's own "interpretation" of things. If I'm moving with respect to you at significant speed compared to speed of light - you will say that my vector is more aligned with "space" and that my time goes more slowly - but in my frame of reference - my direction will be completely in direction of time as I'll be stationary with respect to it - nothing will slow down for me - time will flow normally.

As far as we know - c is a constant and always was.

Only if you are away from that mass and looking at the clock next to that mass. If you were standing on surface of neutron star - your clock would tick rather normally to you - it would be the rest of universe that is "sped up". By the way - there is very interesting thing that this leads to - and that is: falling into black hole will make all universe until its end, "play out" in front of your eyes. Similarly - for observer looking at you falling into the black hole - you'll sort of stay frozen close to event horizon slowly fading out of view (red shift).

Well - there is this thought experiment - let's call it "If one could ride on a photon" and it goes something like this: photon is traveling at the speed of light - so the rest of universe is traveling at the speed of light with respect to that photon in opposite direction. Given that we have dilation of time for systems traveling very fast and when system is traveling at the speed of light - time slows down to a stop. Photon "sees" the rest of universe being effectively frozen in time. Whatever time "passes" in reference frame of that photon - it is irrelevant as nothing else could be used to time it - as everything else is at stand still - that leads to conclusion that no "effective" time flows in reference frame of a photon. Extrapolation of this reasoning is that photon is just "energy transfer cord" between two space time coordinates - when particles exchange a photon they effectively "touch" across space and time (does this count as time travel? ).

Can you expand a bit on that please? In most of the physics - energy is conserved so it can't be function of time. Energy is tied to the time in following ways: - conservation laws stem from different symmetries, and energy conservation stems from time symmetry (which just means that you can't start experiment at any given t0 - you can assign any number as start time and that won't change result of experiment). - energy-time is uncertainty pair. You can't short lived system with well defined energy

Actual formula goes like this: Where m0 is rest mass For photon with no rest mass above turns into E = pc Or other known form of that equation: (energy of photon depends on its frequency / wavelength). In case particle is at rest, so momentum is 0, above equation simplifies to well known E=mc2 https://en.wikipedia.org/wiki/Energy–momentum_relation

Well - I did try to point out one of issues with time travel. Fact that time is "fluid" in GR/SR just points to the fact that time is nothing more than "rate" of interactions. We seem to often think in terms of "monolithic" time - as in "time waits for no man" - it "flows" whether there is something present or not. I don't think that is true - for one thing - there is always something present even if "nothing" is there - quantum fields are omni present and fluctuations in those fields represent passage of time. We can pose following question - if we have stationary system - empty or not, it does not matter - if we can imagine some sort of "spherical particles" suspended in space that don't move with respect to one another - no gravity, just like "frozen" image - frozen in time. Does time flow for such system? If it does - how long has such system been like that? There is no way to tell - no way to indicate passage of time (unless we stand outside of that system with a clock that moves - so there must be something interacting / moving in order for time as something meaningful to exist). If we accept that time is merely rate of interactions in the system - the fluidity of time is nothing special - we don't interact the same with stationary things and moving things, so rate of interaction is not necessarily the same. Given that time is just rate of interaction and one more thing - there must be ordered set of sorts. We know what came before / after - regardless of direction - there is sequence of events - that follow in order. Given those two things - we can see that what we think of "time travel" is just - resetting system to some previous configuration. Either by reversing order of things - CPT symmetry thing - we reverse charge of every particle in universe, we inverse momentum of each particle in universe and we inverse parity - and whole universe will start running in reverse - when we "reach" wanted point - we flip CPT again. In order for that to happen - we must be able to somehow: 1. exclude ourselves from the universe and its laws 2. flip CPT switch at our discretion (don't even want to know what sort of energy would be needed for reversal of all momenta) Another thing is of course to "rearrange" all the particles in universe in configuration that they were in at wanted point in time - that again requires: 1. us being able to exclude ourselves from the rest of universe 2. have a blue print of what the universe was like at wanted time - all the particles with their positions and momenta 3. have enormous energy to rearrange current state of universe to that state. In either of these - we would need mechanism to remove old selves from the universe and replace with current selves that were outside of the universe when flip happened. Type two with non deterministic universe allows for "time lines / time branches".

Laws of physics on tiniest scales simply don't have preference for direction of time. Formulae and laws work same if you introduce certain symmetries. Look at CPT symmetry - if you reverse charge, parity and time - everything still works as it should.

I'm not really comfortable with this assertion. Can you point out things that are proven incorrect in past 5 years? I certainly feel that out of volume of my knowledge - 7% was not proven to be wrong.

I don't have any more questions - but I am very interested in your observation that objects appear brighter in larger aperture telescope for the same exit pupil. When you say brighter - do you mean brighter than surrounding sky or brighter in general? Does the contrast somehow increase in large aperture scope or do both sky and target seem to be brighter in larger aperture scope (say M42 for example)? Brightness on is own is very hard to asses - it's like saying that one sound was louder than the other - without comparing them side by side. Very difficult to tell for small intensity changes but very obvious on for very large changes (say whispering and shouting - you can't really miss that one is louder than the other - even if you don't hear them side by side).

If you do full worm cycle at particular exposure length - it is then easy to see what percentage of subs will be affected by PE. After capturing exposures to cover full worm cycle, you can then make something like this: Some subs will look like this: and some subs will look like this: and you can count the subs and get approximate rejection rate depending on your exposure length. If you wonder if 30s will expose PE - that depends on setup and working resolution. Just as exercise we can do 8 minute calculation of 30s at 2"/px with mount that has 15" P2P error. That is 16 exposures and periodic error covers 30 arc seconds (15" P2P in one direction and 15" P2P - that is 30" of "travel"). If periodic error is perfectly smooth (saw tooth pattern) - each sub will have just under one pixel of elongation. That is not something that will be seen. However - periodic error is not smooth and resembles more sine wave - which has parts where it changes slowly (at peak or trough) and slopes where it changes fast. At these fast changing points - error will be 2-3 times larger then average. 2-3 pixels of elongation will show. So even with 15" P2P - some of 30s exposures will see some trailing, and it is not uncommon for EQ5, EQ6 and HEQ5 class mounts to have 30" P2P.

If uncooled camera will work on USB 2.0 port - then it draws max 0.5A on 5V. If it can work only on USB 3.0 - then it draws max 0.9A at 5V. As for ZWO computer - look at the specs on their website: They recommend (quite wide range) 2-5A at 12V This is probably due to 12V ports that it provides - maybe base consumption is 2A at 12V and other 3A are for these additional ports?

Just mentioning this to @Rustang because of our our recent discussion. Bresser frac and Baader solar film, and excellent results achieved.

Copernicus has good prediction of aerosol and other things https://atmosphere.copernicus.eu/charts/cams/aerosol-forecasts Basic chart gives you AOD at 550nm You have a legend at the bottom - color coded in AOD magnitudes. For usage refer to this text: https://skyandtelescope.org/astronomy-resources/transparency-and-atmospheric-extinction/ This allows you to either get the idea of how clear the skies will be on particular night - or to calculate extinction if you need to do some advanced calculations - like SNR/exposure time and so on.

Wanna do that sort of thing? Here is thread for you

Think of it as push / pull system Loosen central screw that holds ring to dovetail bar and then "adjust" it with other two screws and when those are in position - tighten central screw again to hold it all together. Two screws on the side don't do the bolting - they just serve as "shims"

Let's just for moment think about what time travel actually means and what it implies. Usually when we think about time travel - we simply mean - we "go back" - to yesterday - and everything in world and universe is as it was at some point in time - yesterday. All atoms, and all particles and everything is at the point it was in that instant. Question is - how do we accomplish that? There are two obvious ways to do it: 1. We take every particle in the universe and we reposition it so that it is in exact same configuration it was at instant in the past 2. We somehow reverse arrow of time and let universe "rewind" itself to previous state and then we "let it go" again First approach is obviously impossible - we simply lack the energy to move each particle to wanted position - we also lack means of recording each particle position in the universe to be able to reconstruct exact time moment Second approach implies that there is only one traceable path for particles to move - since we can rewind the universe - which in turn tells us that universe is deterministic - which means there are no parallel timelines and only possible things are perfect time travel loops. Whenever we go back to the past - we will do exactly the things that will lead us to again some time in the future - go in past again. We won't have option to do otherwise as we live in deterministic universe.

Do mythical creatures count? Still in Ubuntu style, presenting merry mermaid:

In the spirit of Ubuntu releases I name this one: Chasing Cheetah

I think your collimation is fine. SCTs focus by moving primary mirror. There is long screw that serves as the lead screw for mirror assembly. My guess is that this screw is somehow damaged or out of alignment on one part of its run. When using it visually - focus position due to optical path is such that mirror separation does not get primary mirror assembly to the section of lead screw that is bent or otherwise damaged. If you put less items in optical path - primary needs to move further to focus at that position and you hit the rough spot. Here is diagram of SCT focusing assembly: It is either threaded rod that is damaged on one section or sleeve / baffle tube contact. Simplest solution is to figure out how much optical path does not create a problem and allows you to focus your camera and then use extension in optical path. Other option is to open the scope and figure out if you can solve mechanical issue.

Actually we are language neighbors Finnish belongs to Finno-Ugric group of languages (also know as Uralic languages): https://en.wikipedia.org/wiki/Finno-Ugric_languages Other prominent member of the group is Hungarian - (Ugric part of the name), and our first neighbor over here. In fact - I'm in a part of the country (Vojvodina) where Hungarians represent second largest ethnic group after Serbs - 13% of people in Vojvodina are Hungarians. I had the privilege of learning Hungarian language in elementary school for 4 years - sadly, I don't remember much of it since I did not speak it actively.

I'd be happy with that S as genuine feature: Here it is in reference image: source: https://www.nasa.gov/feature/goddard/2017/messier-82-the-cigar-galaxy Rest of it might be a little far fetched ...

Maybe wrong bayer pattern used when debayering? That can mess up the colors - yellow and blue seem to have switched their places - usually core of the galaxy is rich in yellow stars and outer arms have bluish hot young stars.