dawson Posted July 14, 2013 Share Posted July 14, 2013 (edited) Does the goto system on my mount take into account any parallax effect, when the relative positions of the stars change by very small amounts as the earth circles the sun? James Edited July 14, 2013 by dawson Link to comment Share on other sites More sharing options...
Tibbz2 Posted July 14, 2013 Share Posted July 14, 2013 (edited) From what I have found the parallax effect is 1 arcsecond on an object 1 parsec away (3.26 ly), and seeing as the nearest star is more than that, I highly doubt that it is something goto systems need to take into account because its so small! (this is annual parallax, which i'm guessing is the most the star/object moves over a full orbit or something) You can also find out the parallax of a star if that's your kind of thing with: distance (parsecs) = 1 / parallax (arcsecs) And a copy and paste for you: The angles involved in these calculations are very small and thus difficult to measure. The nearest star to the Sun (and thus the star with the largest parallax), Proxima Centauri, has a parallax of 0.7687 ± 0.0003 arcsec. This angle is approximately that subtended by an object 2 centimeters in diameter located 5.3 kilometers away. Edited July 14, 2013 by Tibbz2 Link to comment Share on other sites More sharing options...
dawson Posted July 14, 2013 Author Share Posted July 14, 2013 I suspected it was a pretty small variation, but it can still be measured apparently by top notch kit; not by a BBQ on hinges... What is the 'driving resolution' of a mount, as measured in arc seconds? Driving Resolution: 0.1436 arc secondFrom: http://www.firstlightoptics.com/skywatcher-mounts/skywatcher-az-eq6-mount.html James Link to comment Share on other sites More sharing options...
Tibbz2 Posted July 14, 2013 Share Posted July 14, 2013 0.14 arcsecs is pretty accurate, more accurate than I imagined, however if the annual parallax of the closest star is 0.7 arcsecs (and that's down south anyway) then it will probably only be noticeable on very very few stars... I don't know anything about mounts but I doubted such a tiny tiny matter would be implemented in 'amateur' kits... Link to comment Share on other sites More sharing options...
dawson Posted July 14, 2013 Author Share Posted July 14, 2013 But what does that term mean? I can't find a definition for it online. 'Driving resolution'?! JD Link to comment Share on other sites More sharing options...
Tibbz2 Posted July 14, 2013 Share Posted July 14, 2013 Oh right lol! I can't find anything on it, but I guess it's the smallest rotations the mount can make or be measured or something? Link to comment Share on other sites More sharing options...
dawson Posted July 14, 2013 Author Share Posted July 14, 2013 That would make sense, the small movement it can make. I would be interested to know what the accuracy of the GOTO computer is. Does it GOTO an object with arc second accuracy, or just arc minute accuracy? JD Link to comment Share on other sites More sharing options...
Tibbz2 Posted July 14, 2013 Share Posted July 14, 2013 I would think it is possible some go to arcsecond accuracy, seeing as the resolution is smaller than an arcsecond by quite a bit Link to comment Share on other sites More sharing options...
Guest peepshow Posted July 15, 2013 Share Posted July 15, 2013 I always find it very difficult to get my head around these tiny angles and vast distances. So I scale them down to size ! It's about 186 million miles across on our journey around the Sun. That is about 15 light minutes. Take Proxima, as an example, which is 4.25 light years away which is approx 2 million light minutes. So the relationship between Proxima distance and our orbit size is a ratio of 144,000 to 1 Scaling that right down that is an angle of 1 inch base and 2 .5 miles long. Quite a tiny angle but I find it now easier to visualize. I hope my very rough calcs are right. Link to comment Share on other sites More sharing options...
dawson Posted July 15, 2013 Author Share Posted July 15, 2013 No that is useful, thank you. So if i was looking at something 2.5 miles away theough my scope, the position of the star at the two extremes would be one inch? I doubt i could differentiate a one inch gap at 2.5 miles by eye or if imaging. But i'd be interested to know what spatial differentiation (in inches) i could discern at 2.5 miles. A foot? A metre? That still doesn't answer the question though whether the GOTO takes parallax into account or not, which if it did would make the equations much more complicated presumabely. James Link to comment Share on other sites More sharing options...
Guest peepshow Posted July 15, 2013 Share Posted July 15, 2013 No, the naked eye can only make out an inch resolution at roughly 100 odd feet......well my ol' eyes can just about do that, and that's with glasses on It's amazing, isn't it, that the central part of the eye which resolves all fine detail is such a tiny, tine area on the retina. No more than a few thou. Now I'm getting off topic. Sorry,can't help on the GOTO. Link to comment Share on other sites More sharing options...
dawson Posted July 15, 2013 Author Share Posted July 15, 2013 No, i meant looking through the telescope, not with naked eye, sorry. I can barely make put what is tge other side of the room qothout my glasses on!!!!! Link to comment Share on other sites More sharing options...
Tibbz2 Posted July 15, 2013 Share Posted July 15, 2013 (edited) I can't read 'normal' sized text like in books from more than a foot away! Edited July 15, 2013 by Tibbz2 Link to comment Share on other sites More sharing options...
Guest peepshow Posted July 15, 2013 Share Posted July 15, 2013 (edited) So if i was looking at something 2.5 miles away theough my scope, the position of the star at the two extremes would be one inch? No I don't think so. Not 1 inch in a scope. It was the angular change looking at Proxima over a six month period (when we are on the other side of the Sun) , that is the same as the angle subtended by either side of a 1 inch object at 2.5 miles away. It was just a scaled down example to try and get one's head around these tiny angular changes. The only way I can get my head around the Universe is to bring it down to size so that I can visualize it. So we had two similar triangles but vastly different in size ! Try it out on other distances etc. Make the Earth the size of a pin head, for example, and co relate that reduction to the planets and stars etc. I would give some more examples but it's off topic and it's too hot to work Edited July 15, 2013 by peepshow Link to comment Share on other sites More sharing options...
dawson Posted July 15, 2013 Author Share Posted July 15, 2013 Sorry, again i think my poor typing has led to confusion. If two pencils were stood upright, one inch apart, and then viewed theough a telescope based 2.5 miles away; is the movement of the star, due to parallax, effectively jumping from the tip of pencil one to the tip of pencil two, as biewed in said telescope 2.5 miles away, which i suspect would be indisguishly different in the scope. I don't think i'd even be able to see a pencil in my scope at 2.5 miles, let alone differenate one pencil from another when they were just one inch away from each other. James Link to comment Share on other sites More sharing options...
Tweedledee Posted July 15, 2013 Share Posted July 15, 2013 If two pencils were stood upright, one inch apart, and then viewed theough a telescope based 2.5 miles away; is the movement of the star, due to parallax, effectively jumping from the tip of pencil one to the tip of pencil two, as biewed in said telescope 2.5 miles away, which i suspect would be indisguishly different in the scope. James Hi James, Your above statement is correct. I just ran through Richards calculations with my rum and coke (hic!), and can confirm his numbers are as near as makes no difference. Most larger amateur scopes will nearly, but not quite resolve two stars at this tiny separation, approx. 0.7 arcsecs. This parallax angle is for the nearest star, and other stars are much further away, so if you want to examine the parallax on Deneb for instance, over 2000 light years away, you would need to resolve down to about 0.002 arcsecs, and be able to set up and maintain your equipment with such accuracy for a period of 6 months! So the parallax is going to make no difference to the positioning of a goto mount. Any polar alignment will not give anything like a 1 arcsec accuracy. I also use Richards methods to scale down and understand the sizes of things in the universe, it works really well if you enjoy doing the calcs. Link to comment Share on other sites More sharing options...
dawson Posted July 15, 2013 Author Share Posted July 15, 2013 I see. I clearly need to take up rum, whiskey a d other shorts; will it make me good at these sums like you two Thanks. James Link to comment Share on other sites More sharing options...
Tweedledee Posted July 15, 2013 Share Posted July 15, 2013 It might, provided you can maintain a mental calculation of exactly how many units you have consumed, and can accurately establish the point at which your blood alcohol level will cause a calculation overflow error in your brain making further calculations totally invalid . Practice, practice, practice . Link to comment Share on other sites More sharing options...
dawson Posted July 15, 2013 Author Share Posted July 15, 2013 Wax on, wax off Link to comment Share on other sites More sharing options...
Tweedledee Posted July 15, 2013 Share Posted July 15, 2013 Karate Kid Link to comment Share on other sites More sharing options...
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