andrew s

That is not how I understand things. There is a wobble superimposed on the axial procession. I suspect we are using terms differently. To be honest I don't feel motivated to take this further. Regards Andrew

It's measured relative to the dates of the highest and lowest points the Sun gets to over the year and it was noticed hence the Gregorian Calendar. Regards Andrew

That's not what wiki says it is the axial procession it corrects for it does not correct for changes in the earths rotation rate. Regards Andrew

Just had a quick look at "Axial precession " on Wiki it gives a good explanation of the shift but does not comment on why the date does not change. I would guess that it is corrected to a degree with the leap years of the Gergorian calendar. Again looking at Wiki that what it was aimed to do keep the calendar aligned with the equinoxes. Regards Andrew

Plate solving will tell you where the mount is pointing to the accuracy you require but that is different to pointing to that accuracy. However this will be based on an epoch 2000 catalogue. I am not up enough on orbital mechanics to advise why the date has not changed. Certainly where on the horizon the sun rises on the day of the solstice has shifted but without further study I can't add any more. Regards Andrew

Telescope pointing can be in the 10s of arc seconds so yes but you need a reference normally done by a catalogue of stars. The reference basis is a set of distant Quasars . The day of the solstice does change. There are several causes, try googling. Regards Andrew

I don't think it is as simple as measuring the position of a star as you need to measure it relative to the earths axis.. You could try measuring the position of Polaris over a night in alt AZ coordinates and find where the centre of its motion is. Then repeating a year or more late. You would have to watch out that measuring method did not already assume the rate as planiterium software often does calculation from position "now" to a given epoch generally 2000. Regards Andrew

@ollypenrice point about field rotation is correct if you are guiding. It's not an issue if just tracking. There are other types of error due to the apparent sidereal rate being different in different parts of the sky and you get the apparant celestial pole moving with altitude which are both elliminated by guiding when the guide scope and camera are aligned. I think the best approach is to just try it. Experiment is king in these situations Regards Andrew

The solar observation were from the IBEX satellite not remote observation so we have not been able to measured this effect on any other stars. Regards Andrew

I remember articles on building mounts from gas pipes and fittings. Lapping the threads to make smooth bearings. Now we have CNC machines and 3 D printing but still room for creative use of everyday items. Regards Andrew

That's my kind of engineering. Excellent work. Regards Andrew

Nice idea but I found the human component incapable of finding anything . Regards Andrew

Notwithstanding, issues with specific mounts, it might be worth pondering on the fact that to point at a star and track it with or without guiding reliably is a very complex task. Whatever the design it requires precision engineering, robust and complex firmware and electromechanical components and often similarly complex computer software. Many issues reported here and elsewhere are due to the interface between these components especially when they are from different manufacturers/suppliers. Unfortunately, it is often the case that end users are stuck in the middle trying to diagnose the problem. Two examples, one when I was telecomms manager and my team were being slated for a network being unreliable. It turned out the two Vax computer at either end had incompatible time outs. The second where I could not get The Sky 6 to correctly set the time on a AP controller on a Parallax mount. I got a detailed lesson from the AP firmware specialist on how to calculate local hour angle from sidereal time etc. Eventually, I found an error in his code that did the sums wrong if you happened to be in the zero time zone. This had not been fixed some years later when I had an AP900 for a while. My advice, for what it is worth, is to minimise the number of components as much as possible. Regards Andrew

Great talk @JeremyS had to duck out during the questions but very well done. Regards Andrew

Very nice observation. Regards Andrew

Now what fiendish question can I think up? Seriously, good luck I am sure it will be a treat for us all. Regards Andrew

Not withstanding recent issues with their new web site I have found Software Bisque to have a good after sales service. They have been very good at helping with both hardware and software issue over a number of years. Regards Andrew

All the best data gathering is done while asleep in my view. Stops you biasing the results! Regards Andrew

Very nice work, I like the various ways of displaying your data especially the light curve. Regards Andrew

Interesting, never come across that. Can you provide a reference so I can follow it up. Regards Andrew

Venus is never far from the Sun so you can see it in the evening in the West as the Sun sets and in the East before and as the Sun rises. Regards Andrew

Maybe a challenge for modern observers would be to do a mosaic with close to optimal lighting across the whole face? Regards Andrew

Quite right, but it was done before digital technology. The photos were from the 36" refractor. A very impressive bit of engineering. Regards Andrew

Just to be clear no digital trickery was used. Regards Andrew

While tidying up I came across this picture of the moon I got on a visit to the Lick Observatory. Can you spot what they have done. Regards Andrew