Magnetic south

[Marcus]

Hi
I have searched the forums but only got more confused.
In Caulfield (Melbourne) where do I point my scope for polar alignment? I understand I need to point my scope Southeast, 12 degrees to the left if facing 'south'. That seems to work but not quite.

[bartman]

Hi Marcus,
What do you mean by "not quite"?
Have you done a drift align or similar?
Bartman

[andyc]

If you're familiar with the principle of magnetic declination (angle between the geographic and magnetic poles), you can get the current declination value from websites like http://magnetic-declination.com/ . Not sure just how accurate that site is, but look around and see if there's a better site! Note that declinations vary year-to-year as the magnetic pole wanders a bit.

That should get you approximately pointing south using a compass, but also beware of metallic objects near your compass, perhaps including telescopes (!), which will muck up the accuracy of your pointing if using a magnetic compass (see images here for an example http://www.trailmeister.com/HelpfulTips/Howtousecompass.htm).

Techniques like drift alignment as bartman suggests would probably be necessary to get a more accurate polar alignment, also accounting for the altitude of the pole above the horizon.

[bartman]

+1 to Andy !

[mithrandir]

That site assumes you are whereever the office of your ISP is located. For Australia, GA has the official figures (http://www.ga.gov.au/oracle/geomag/agrfform.jsp).

Caulfield, Victoria
Requested: Latitude -37o 53' 00", Longitude 145o 2' 00", Elevation 0 km, Date 2012/11/16
Calculated: Latitude -37.8833o, Longitude +145.0333o, Elevation 0.00 km, Epoch 2012.8743

Magnetic Field Components
D = 11.574 deg
dD = -0.006 deg/yr

[Marcus]

I mean 'not quite' as I was pointing off to the left but could only tell using a DSLR photo due to LP.

I just want to check whether its 180 MINUS 11.574 = 169 not plus, i take it it is. Obviously i need to get a better compass than the one in my iPad. Having fixed my finderscope I will try a drift align next.

[Rob P]

Hi Marcus,

Had to get my head around this when I was at sea.

I was taught to use CADET: Compass to True ADd East

Assuming a deviation of 11.5°E

Compass Bearing : Deviation : True Bearing
168.5° : 11.5° : 180°

Hope this helps.

Rob