Field rotation question

[The Admiral]

14 hours ago, RobertI said:

I've had a go at translating the graph into a very rough map

I agree Robert, it is an interesting spherical geometry problem that is quite difficult to get one's head around (the same reason I can't visualize EQ mount movements ). It did occur to me that if I could take my data and plot it on polar coordinates it would be much easier to visualize. Well, it would be, except Excel doesn't chart in polar coordinates (how daft is that?)! There are cludges to work around it, but my feeble brain at the moment is struggling and it's taking up too much time. It's a problem I'd like to sort, but not today!

Ian

Edit. May be the Radar Chart will do it?

[RobertI]

4 hours ago, The Admiral said:

I agree Robert, it is an interesting spherical geometry problem that is quite difficult to get one's head around (the same reason I can't visualize EQ mount movements ). It did occur to me that if I could take my data and plot it on polar coordinates it would be much easier to visualize. Well, it would be, except Excel doesn't chart in polar coordinates (how daft is that?)! There are cludges to work around it, but my feeble brain at the moment is struggling and it's taking up too much time. It's a problem I'd like to sort, but not today!

Ian

Edit. May be the Radar Chart will do it?

Ha ha, yes my brain has been struggling with it too, so counter-intuitive. I suspect your Excel skills are far better than mine, hopefully one of us will crack a better visualisation at some point.  

[The Admiral]

On 29/07/2018 at 11:56, The Admiral said:

It's a problem I'd like to sort, but not today!

Edit. No what I had posted earlier is patently not correct as the time gets longer the closer to the zenith. This will need looking at again.

But today I tried! Well, here's a half-decent attempt to show the regions of the sky in relation to field rotation. I had to use a demo contour mapping plug-in with Excel to get this, hence the over-writing!

Ian

 

[RobertI]

My head just exploded! ? Thanks for trying though!

[RobertI]

I guess the problem was the 0 degrees altitude being at the centre and 90 degrees being at the horizon, it was kind of inside out?

[The Admiral]

40 minutes ago, RobertI said:

I guess the problem was the 0 degrees altitude being at the centre and 90 degrees being at the horizon, it was kind of inside out?

Indeed, it wasn't just the scale but the data as well! I'm not sure how addressable that will be with the demo software. Need to think about that one.

Ian

[The Admiral]

12 hours ago, RobertI said:

I guess the problem was the 0 degrees altitude being at the centre and 90 degrees being at the horizon, it was kind of inside out?

Right, it was an itch that just had to be scratched . I can see where I went wrong, but I think the map shown below is now correct. All except for the scale which has 90 at the horizon, whereas it should be 0°. I can't change that with the demo software. But the data is the correct way around now, or should be! The mapping software has thrown up some odd artefacts, particularly near the zenith; you'll have to ignore those. But your sketch was essentially correct. The N-S axis is horizontal, the E-W axis is vertical.

To re-iterate, I've plotted the number of seconds for a 0.1° field rotation. It is based on calculations for elevations from 0° to 80° in 10° steps, and 10° steps in azimuth.

I can rest easy now

Ian

[RobertI]

1 hour ago, The Admiral said:

Right, it was an itch that just had to be scratched . I can see where I went wrong, but I think the map shown below is now correct. All except for the scale which has 90 at the horizon, whereas it should be 0°. I can't change that with the demo software. But the data is the correct way around now, or should be! The mapping software has thrown up some odd artefacts, particularly near the zenith; you'll have to ignore those. But your sketch was essentially correct. The N-S axis is horizontal, the E-W axis is vertical.

To re-iterate, I've plotted the number of seconds for a 0.1° field rotation. It is based on calculations for elevations from 0° to 80° in 10° steps, and 10° steps in azimuth.

I can rest easy now

Ian

Brilliant result Ian, I think this demonstrates perfectly how field rotation varies across the celestial sphere. I've never seen it presented in this way, so hopefully this will be of benefit to others in the future. Personally I now feel much better informed, and it's nice to be able to be able to look into the sky and know where the 'no fly zones' might be .