Aligning an Astrotrac with a compass?

[maxwolfie (Greg)]

Hi All,

I've recently bought an Astrotrac, I've yet to try it out as the compass on my iPhone isn't very good (surprise surprise). Anyways, I need to buy a compass. I also know that I need to know the magnetic deviation for my area, as follows:

Latitude: 33° 49' 0" S
Longitude: 150° 58' 0" E
Magnetic declination: 12° 26' EAST
Declination is POSITIVE
Inclination: -64° 16'
Magnetic field strength: 57130.9 nT

My question is, what does all this MEAN? Do I need to calibrate my compass (that I haven't bought yet!) with the above?

And, what TYPE of compass is required? It would need to work at an angle. What's a good/cheap compass that will do the job, if such a thing exists? I'm in Australia, but happy to order online, provided freight is cheap.

[rolls05 (Roland)]

G'day Greg. I can only help with the compass. Buy an Android phone. As for the rest, I await with bated breath as I like the look of those. Or maybe a polarie.

[silv (Annette)]

The compass will point to the magnetic pole of the earth - which is not identical with the celestial pole, e.g. "true south".
You simply turn the compass such that the needle sits on 12 degrees east of S. That direction then is "true south".

Here, the solar noon method as well as the compass emthod are described.

(I bought a simple compass from an outdoor store. But it turned out that my iPhone compass is indeed just as accurate when set to "true north".
Location service: on- Wifi and Bluetooth: off.
I also downloaded Commander Compass Lite which has the advantage of showing whether the iPhone is held level. It can be set to "true north" instead of magnetic north. Then, the needle already points to the SCP when it sits on S - it has then internally adjusted for the declination of your 12.x degrees.

For my mount setup in the drive way, the solar noon method proved to be the best because then I have a long line on the concrete to help me with the orientation of my mount.)

[silv (Annette)]

the Astrotrak will cause interference with any compass, iPhone or other.
stay clear of any metal while handling the compass.

[rogerg (Roger)]

I have a SILVA compass which works very well. Something like this:

http://store.silvacompass.com/produc...65/Polaris_177

[mikerr (Michael)]

The Solar noon method is easy if the sun is not blocked from you at your location.
al's astroclock ....http://www.iceinspace.com.au/files.html

will give you Solar Noon. You can set a spare watch to the solar time and take it out with you when you go out to mark the shadow.

Michael

[Poita (Peter)]

You are in luck, in Sydney from today until the 11th Solar Noon is at 12:01
Then solar noon is actually at noon until from the 12th to the 15th.

You can literally just stand up straight at Solar Noon and your shadow will fall precisely North/South, no adjustments needed.

If you want a more exact shadow you can hand a plumb-bob on a string and the string shadow will be North/South at noon.


Solar Noon for Sydney for the rest of the month:
http://www.timeanddate.com/worldcloc...&afl=-11&day=1