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Hi Jack,
I recently had to do this for a meteor camera installation, needed to a couple of metres accuracy. The recommendation was Google Earth
https://earth.google.com/
Zoom into your exact location, right click and click info in the pop up boxCheers
Robinnote the default setting only gives the location in deg,min,sec to one second resolution. If you need higher resolution switch to decimal degrees (tools ,settings, formats and units, lat lon format, decimal) this then give the location in degrees to 6 decimal places (less than a metre)
EDIT, looking at some papers on this the actual absolute accuracy though is probably more like 5-10m in position and a couple of metres in elevation
Cheers
RobinI used the Ordnance Survey OS Locate app on my phone – gives lat / long to 4 decimal places and altitude in metres to 1 decimal place.
Callum
Yes, Google Earth is probably best. The lat/long in Google Earth is WGS84 and its georeferencing is accurate at the few metres level over much of the UK (mainly the flat bits since projection on mountains is much harder). A few years ago I checked this for my telescope using a surveying SBAS/GNSS receiver which, ultimately, is cm level accurate in WGS84 if you leave it long enough. The position it got was around 1.5m from the position I read from GE and about 6m different in height although I couldn’t work out which geoid reference it was using.
For most astronomical purposes, apart from very precise astrometry of near objects and meteor triangulation, you don’t need that kind of accuracy. In any case, at the metre level you need to be very careful what system you use. Lat/Long is generally WGS84 but height depends on the exact reference geoid and, for instance, the GMN meteor camera network uses EGM96. I think the difference between those two can be 10s of metres (height) in some places.
I use Google maps. At full zoom a position can be located to within 10m in most parts of the civilized world and in most of the US for that matter.
Right now I am sitting at 52.143392N,0.117095E and my car is parked at 52.143390 0.117336E.
The difference in latitude is .000002 degrees and at 60 nautical miles per degree, or 111.12 km, that is 22cm. The difference in longitude is 0.000241 degrees but that must be divided by cos(latitude) to convert to an angular separation. The conversion factor is 0.613254320 according to my good old Chambers 7-figure log tables. Performing the division and multiplication yields a linear separation of 44m. In reality the car is about 1m north of me but the east-west distance is actually about 18m.
Good enough for me. Note that one arcsecond is 112120 / 3600 = 31m so my co-ordinates are good to an arcsecond or better.
A conundrum Google Earth says 51.59 36 0.60 77 The SkyX X says 51.37 45 0.36 27.
Question: If TheSkyX co ordinates are wrong would that explain why the target is not dead centre in the field of view.
It has a T point model.
Which one is correct?
JackNor can I. Not sure where it went.
Bottom line: Google Earth is your best bet as TheSky doesn’t (I don’t think) talk to a GPS dongle, so any location it has for you will be from an IP address or the nearest town long/lat. I could be wrong here.
Note though, that time and location are both important. You need a good position and good times. So, to get accurate pointing:
1, Set the computer system clock using its “Change date and time” setting.
2, Start TheSkyX
3, Set your location to the Google Earth value
4, Do your 100+ pointings T-Point run.And whenever you use the telescope set the time again just before running TheSkyX – its an essential. Many laptops/PC lose multiple seconds over a week or two between observing sessions – some do better than others.
Not sure what mount you are using, but a Paramount MEII does far better at absolute pointing (after T-Point) than my regular NEQ6 which was good to 1 arc mins on the west sky last night but a lot further out on the east part of the sky. The mount quality is a big factor. If your mount is not entirely consistent even T-Point cannot make it perfect.
Note though, that time and location are both important. You need a good position and good times. So, to get accurate pointing:
1, Set the computer system clock using its “Change date and time” setting.
…Remember to activate your NTP client (operating system dependent) and configure it to use reliable low-stratum servers.
My Win10 TCS is rarely more than 20ms from reality and my Linux boxen are usually under 5ms — the one I am using now claims to be 0.214ms away from GPS time..
Grant and Paul,
Its a Paramount MX with a 70 star T point model.
I use http://www.thinkman.com/dimension4/default.htm to set the clock.
Question for Grant: Are you saying that if I change my lat lon location in TheSkyX I have to do another T point run?
Regards,
JackYou should be able to sync into the existing T-Point model, but given that when using the automated platesolving mode it takes less than an hour for a full T-Point run, I would be inclined to redo the T-Point from scratch. Just wait for a night with thin cloud or full Moon thats no good for anything else. I find 1-2second images are easily deep enough. I just listen to music on headphones while manually rotating the slit to ensure the scope sees skies – the joys of a non-automated early Pulsar.
IF with an accurate time and an accurate position you still have issues it will help focus your attention a bit.
Just bought a second hand MX, but have not yet installed. Hopefully a lot better pointing than the NEQ6.
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