(another) Drift Alignment Q

[Notty]

Trying to get my head around this as I've hit the wall where I know I have to do it....I've read various threads that touch on the answer but if anyone can answer definitively?

Regarding star selection. My understanding is you select:

1. one star bang on the S meridian on the equator, close to 0 dec as possible, and

2. One on either bang on E or W point but ideally 20-30 deg of dec.

I know this is written down in a million tutorials but they all seem to assume you've an unimpeded view for 360degs so I can't get exactly E or W. I have various trees and obstructions plus my actual house obscures my view to the S I can only see from about 30 degs up to the south!

Will the procedure work with these limitations?

Thanks as always

[Davey-T]

Hi Notty hows the Solar imaging going ?

You can use any star really just the further from the ideal spot the slower and harder to detect the drift, also not a good idea to use one exactly South as the drift can get confusing, I start a bit East so I can see drift before it reaches dead South.

I also use an illuminated Baader micro guide reticle but you can use an ordinary illuminated reticle and set one axis to match RA then star should follow the reticle line, if it drifts off just adjust the mount to bring it back to the line, if you go too far it will start drifting the other way.

PHD has a Polar aligning routine and DARV is another mathod using a camera, I just prefer using the illuminated reticle.

ATM you could use Alphekka and Regulus

Also remember the drift in the East is towards or away from Polaris, ie: not magnetic North and South.

Dave

[wxsatuser]

The celestial equator due south is approx 40degs above the horizon in the UK.

I normally use a star just east of the meridian.

Cannot see west here and my east horizon starts at about 20degs altitude.

For the east star I chose a star thats near the celestial equator but at an altitude of 20degs, this

means the star is more towards the south east.......this still works ok.

BTW I use PHD to drift.

[kens]

The idea is to get as close to 0 dec (the Celestial equator) as you can as that shows the biggest movement for a given error.

For azimuth error you want to be close to the meridian as this minimises the drift from altitude errors.

For altitude error you want to be close to the horizon as this minimises the drift from azimuth errors.

If you not spot on that's ok - just makes it slightly harder to spot small errors and to separate out altitude and azimuth errors

Like others I start East of the meridian and I use PHD to graph the drift.

My routine is as follows:

Start with the scope in its home position.

Rotate in declination to 0 degrees

Looking through the finder, rotate in RA towards the meridian and when close select a handy star.

Drift and correct for azimuth

When done, rotate in RA back to the Eastern horizon. (I usually find a star close to 0 degrees dec, If not, return to zero degrees dec first)

Looking through the finder, rotate in RA away from the horizon and select the first suitable star.

Drift and correct for altitude.

Rinse and repeat if any big adjustments were needed

[Notty]

Thanks all, but I'm getting more confused... how can the celestial equator be 40degrees above the horizon?? I know that with the scope pointing 90 degrees to the dec axis of the mount that's approximately whe it'll be pointing, but that's just a plane through the earth 40degs north of the equator isn't it?

Last time I looked I wasn't thick... but this business is making me reconsider!!

[beamer3.6m]

How do you guys move the dec to zero. Is this just a case of knowing where zero is or do you use setting circles etc?????

Very confused.

[Davey-T]

Start Stellarium and move the view so East is in the centre of the screen and note the zero dec line coming "out of the ground" if you press the full stop key it will highlight it.

If you now move the view round to the South you will see the zero line climbs into the sky and down again if you keep going. this is the best line to have stars near for drift aligning, not that any are actually on it.

The stars go across the sky following this curve and the idea of drift aligning is to get the mount moving in RA to follow this line and therefore the stars.

Dave

[Notty]

Thanks Davey! Now I can see it with my eyes even if it's counterintuitive to my tiny mind. Solar imaging been very quiet recently as has all astro activity due to work mainly. Trying to get back into it but keep hitting snags... though it looks like that's the standard in this game.

Andy

[wxsatuser]

Thanks all, but I'm getting more confused... how can the celestial equator be 40degrees above the horizon?? I know that with the scope pointing 90 degrees to the dec axis of the mount that's approximately whe it'll be pointing, but that's just a plane through the earth 40degs north of the equator isn't it?

Last time I looked I wasn't thick... but this business is making me reconsider!!

The celestial equator due south is down from the zenith by an angle equal to the latitude.

Here I'm about 51 degrees latitude.........51 from 90 is 39.

[Notty]

You'll be telling me the earth isn't flat next!!

Seriously, thanks. With that major piece of basic misunderstanding sorted, I can soon proceed to tie my brain in knots once I try this drift alignment thing for real.