HI > On Dec 30, 2016, at 4:53 PM, Chris Albertson <[email protected]> > wrote: > > Yes, the below is basically correct. But you save a ton of time and > get better results if you simply bolt the telescope down to the Earth > so that it can't move at all. The aim point just needs to be "close" > and then later you determine where it is aimed. If you are only > measuring period you don't need a surveyed location. If measuring > absolutely time you do. > > Using a fixed mount is what makes this affordable by amateurs. Epoxy > the camera to a fixed masonry building. This removes an unknown and > dramatically simplifies the processing and also saves most of the cost > witch is always the mechanical stuff. One package of JB Weld epoxy > replaces thousands of dollars of motors and encoders and precision > gears. > > With a fixed mount camera you have two kinds of "tine", that observed > by the camera and a second from your GPSDO. If they diverge then you > deduce that it must be the Earth's rotation that changed. But maybe > you wonder of maybe the camera moved or some effect you forgot to > remove. So it is but to have some buddies running the same setup in > different cities around the world and check that you all see the same > results. That is what we did. It is FAR EASIER to do this kind of > replication when the setup is very inexpensive. > > Today you could build a camera for a LOT less then we did. I'm > thinking of a surplus used lens from a 35mm film camera. A 250mm lens > or so and a 3D printed plastic part that holds this to a cheap point > and shoot camera.
If by 3D print you mean a filament machine, pretty much all of the useful filaments will soffen / deform / melt if left in the hot sun for a day. The few that are more temperature tolerant require an unusual printer to work with and are a real pain to work with. One alternative would be a 3D printed mould and a metal casting process. It would take more than a few steps to get to metal. You also would need to clean up the casting before it was of any use. Bob > We used epoxy to held the lens to the camera, it > meant you'd never be abler to take it apart again but it was going on > a roof top, rain and all. > > > On Fri, Dec 30, 2016 at 3:16 AM, Ilia Platone <[email protected]> wrote: >> Bruce, >> >> I think that you refer on prjects like Astrometry plate solving. I think one >> should got a reference to get a time reference instead of scope "pointing" >> reference, so, once one's got local coordinates in encoder positions, for >> example the values of the north pole with an alt/az mounting, can use a >> sub/arcsec plate solver to obtain good sidereal timing reference. using two >> encoders helps much. >> >> The problem can be visibility of the reference points, however. >> >> Best Regards, >> >> Ilia. >> >> >> >> On 12/30/16 10:59, Bruce Griffiths wrote: >>> >>> Attila >>> Lookup "Stellar compass" as used for determining space probe attitude.Can >>> also be used to determine the direction of the centre of an image of a field >>> of bright stars.Subarcsecond accuracy is fairly routine.Pattern recognition >>> techniques combined with measures of the relative brightness of the stars is >>> used to identify them.Subpixel accuracy in determining the location of the >>> stellar image centroids is also routine. >>> There is at least one US PhD thesis on such stellar compass techniques.A >>> stellar compass technique has been used to determine the pointing direction >>> of small portable telescopes without requiring precision axis encoders etc. >>> Bruce >>> >>> On Friday, 30 December 2016 11:43 PM, Attila Kinali >>> <[email protected]> wrote: >>> >>> On Fri, 30 Dec 2016 10:59:03 +0200 >>> Anders Wallin <[email protected]> wrote: >>> >>>> out of curiosity, are there any amateur/semi-pro experiments that can >>>> measure the length of the solar or sidereal day to sub-millisecond >>>> resolution? >>>> To reproduce data like this: >>>> >>>> https://upload.wikimedia.org/wikipedia/commons/5/5b/Deviation_of_day_length_from_SI_day.svg >>>> >>>> Something in the sky that goes "ping" every day - detected with a >>>> pointing >>>> accuracy of < 1ms/24h or <0.01 arc-seconds (!?). Or perhaps two >>>> satellite-dishes pointed at the sun and >>>> noise-correlation/interferometry?? >>> >>> I don't know of any such experiment already performed, but I am not up >>> to date on what's going on in the hobby astronomy community. >>> >>> I am not sure whether sub-milisecond resolution is feasible, but >>> I think the "easiest" method would be to do a "modern" version of >>> an meridian telescope: >>> >>> Using a camera fix mounted (ie not moving and if possible vibration >>> isolated) >>> on a pedestal pointed at the sky, approximately looking south. A simple >>> webcam would be probably enough for first experiments, as long as you get >>> a good picture of the stars. A good compact camera which allows to use >>> a remote shutter with a proper lens and exposure control should be better. >>> Probably the best resource here are the people/websites that deal with >>> book scanning, as they tend to automate the whole picture taking process. >>> Using magic lantern (http://magiclantern.fm) with Canon cameras might >>> give additional features needed for the task. >>> >>>> From the pictures taken, calculate the positions of the stars (by fitting >>> circles onto the bright pixels) and figure out which star is which (using >>> astronomical list of stars). For this step there is a plethora of open >>> source >>> astronomical software available, but I don't know how well they fit the >>> task >>> of figuring out what the position of the stars relative to the camera >>> reference >>> frame. After that, it's just some simple math of calculating the >>> difference >>> between the position of the stars and where you would have expecteded them >>> at the time when the picture has been taken. >>> >>> Some usefull software projects are: >>> http://astro.corlan.net/gcx/ >>> http://www.clearskyinstitute.com/xephem/ >>> http://starlink.eao.hawaii.edu/starlink >>> http://astro.corlan.net/avsomat/index.html >>> http://rhodesmill.org/pyephem/ >>> >>> HTH >>> >>> Attila Kinali >>> >> >> -- >> Ilia Platone >> via Ferrara 54 >> 47841 >> Cattolica (RN), Italy >> Cell +39 349 1075999 >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > > > -- > > Chris Albertson > Redondo Beach, California > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
