Compass drama

[TechnoViking (James)]

Hi All,

I have been out in the OB at every clear sky i get, I have been having a few problems finding the Celestial South pole, I know im close but not close enough and i have think it has something to do with my compass... I have used my Iphone, a Android tablet, my sons scouts compass, and a old naval compass, and when i place them down a good 2 meters apart, they all point in different directions!!! Now im not talking a few degrees, im talking between 10 - 90 degrees!!! which makes working out how many degrees from Magnetic South it is to Celestial South almost an impossibility. There are no metallic objects close and no magnetic interference

I just dont get it!! is there a way of "Sheilding" the compass to prevent this from happening??

Cheers

James

[mithrandir (Andrew)]

There is a better way James. It's called the solar noon method and a quick search brings up these threads:

http://www.iceinspace.com.au/forum/s...ad.php?t=97012

http://www.iceinspace.com.au/forum/s...ad.php?t=97868

http://www.iceinspace.com.au/forum/s...ad.php?t=94997

[Kunama]

James where are you placing the compass, if it is on a concrete slab the needle will respond to the steel reo in the slab and depending on where it is in relation to the reo bars it can point in any direction. Keep the compass at least 500mm above the slab and the plumb down to mark the slab.

[TechnoViking (James)]

Originally Posted by mithrandir

There is a better way James. It's called the solar noon method and a quick search brings up these threads:

Sounds like white man magic I will have to check that out , thanks


Ive tried putting the compass on Grass, Timber, Concrete, ive even tried on to of a wooden table. I will have to take a photo to show this strange phenomenon

[Poita (Peter)]

I've never had any luck with a compass, but the solar noon method gives me a perfect alignment. Just remember to adjust for daylight saving!
In Cobargo on Saturday December 8th Solar noon will be at 12:52:47, on Sunday the 9th at 12:53:14

http://www.solar-noon.com/sn_calc.php?Location=Cobargo&LatDec =26.35&LatNS=S&LongDec=149.8&LongEW =E&TimeZone=-150&Type=SolarNoon

[TechnoViking (James)]

Originally Posted by Poita

I've never had any luck with a compass, but the solar noon method gives me a perfect alignment. Just remember to adjust for daylight saving!
In Cobargo on Saturday December 8th Solar noon will be at 12:52:47, on Sunday the 9th at 12:53:14

http://www.solar-noon.com/sn_calc.php?Location=Cobargo&LatDec =26.35&LatNS=S&LongDec=149.8&LongEW =E&TimeZone=-150&Type=SolarNoon

Wow thanks Peter!!!! I will give it a go on sunday, im guessing the best thing to do is roll off my roof, put a length of timber across the top of the observatory and hang a thick string with a weight off the timber directly over my mount (with the OTA taken off) and then line up the mount to the center of the shadow? and that should get me aligned?

I suppose i can also test it with the Align Master software that i was directed to, to double check that i got it right?

Thanks again guys for your help

[SteveInNZ]

You have a CGEM mount - I have a much simpler method then.

The Celestron mounts have a function called "Quick Align". It's not documented very well but the idea is that you point the scope at the celestial pole with the counterweight down. With the time and location correctly set, select "quick align" and the scope sets itself up from that information.

So you can use that function, but backwards to point the axis at the pole.
With the mount turned off, unlock the RA and move it until the counterweight bar is pointing directly down. Now unlock the Dec and move the scope until it is parallel to the RA (polar) axis.
A simple way to get both of them lined up is a bit of string with a weight (plumbob) on the end of the scope. When the piece of string passes the middle of the counterweight bar, both axis are lined up. Alternatively you can use a bubble level, inclinometer, etc.

Lock both axis, turn on the mount, set the time and location and select quick align. When it says done, tell it to slew to something easy to find and unmistakeable. If it's visible, I use the Jewel Box cluster (NGC 4755).
Now move the scope in Alt and Az (not using the hand control) to get the object into the scope. In doing so, you've moved the polar axis to where the real pole is.

You are now polar aligned enough for visual use and are within a turn or two for photographic use. That means that you won't run out of adjustment when you do a final drift alignment.

I travel out to remote sites to use my scope and this gets me in the ballpark every time, regardless of sloping ground, trees in the way, etc. All I need is my phone (for the inclinometer and GPS) and one visible object.


Steve.

[TechnoViking (James)]

Cheers Steve! I will also give that a go, today is shaping up for a beautiful nights viewing, first clear day in weeks!

I hope i didnt just jinx myself saying that!

with all the methods given to me, I should have no problems now getting SCP centered!

Cheers everyone who has added a comment!

all the best

James

[Dennis]

Hi James

Here is a link to an older post concerning how I can polar align in the daytime to within 1 or 2 degrees of the SCP, using a protractor and a compass. So far, this technique has always placed Sigma Octans nicely in the field of view of the polar alignment ‘scope of my mount.

Cheers

Dennis

[Poita (Peter)]

I didn't realise you had a CGEM. It has a polar alignment routine that works really well. Two iterations and mine was pretty much spot on.

[TechnoViking (James)]

Guys you are Champions!!!!!!!!!!!
Tonight i finally got my GEM polar aligned! I used the Polar Alignment utility in the CGEM menu, followed the instructions, and after only 10 minutes its aligned.

I had tried the Solar Noon, but for some reason I just couldnt get the alignment right, I also tried drift alignment, omg that was the biggest failure (due to my n00bness), i also found that the time was set wrong on the computer i was using in the observatory, which is also why my GOTO was not working correctly, it was out by a full 7 minutes!!

Thank you everyone who gave me hints and tips, i can now track objects very accurately, even after 4 hours of star hopping i can still slew to jupiter very close to center in the illuminated EP.

Thank you all again !!