Azimuth zero and direction in S Hemisphere

[Merlin66 (Ken)]

""Why is it that North is still the Zero direction for Azimuth directions in the Southern Hemisphere and not <our> pole in the South??""
Good question!!?

[The_bluester (Paul)]

Yeah.

I saw similar mentioned recently actually on a link from a thread on IIS. Seems just a convention, like north being up on a map. Otherwise I suppose it would get to be a very blurry line on the equator, which coordinate system to use if you are pretty much on 0 degrees?

[AndrewJ]

Gday Ken

There is no true "convention" on this ( as far as i can see )
Some authors of celestial calculations use Sth as zero ( ie Meeus/Trueblood and Genet ) and others use Nth is zero ( ie Duffet Smith ) .
The arrangement of the calculations to convert RA/DEC to AltAz etc then depend on the convention chosen.
( Meeus notes that the Nth vs Sth convention was different between astronomers and navigators )
I know Meade use the Nth is zero convention, probably so they can match it to the "Level/Nth" start position, so to simplify the internal calcs, Nth is still zero, irrespective of hemisphere.

Andrew

[Wavytone]

A rather more mundane application is surveying - everything from highways down to blocks of land and houses.

North has been zero azimuth for navigation ever since the invention of the magnetic compass, and for good reason. Ptolemy first solved the problems of spherical trigonometry to draw the sphere (earth) as 2D planar maps, with the result north being zero was a simple convention that stuck, and was all the more convenient at night given Polaris.

As noted previously you can choose any reference point you like for zero azimuth - south, due east, or a white mark on the neighbours fence, as long as whatever maths you're doing takes it into account.

What makes a reference for azimuth or altitude really useful is being able to easily identify and use it - which is why north = 0 was so easily - Polaris plus every magnetic compass gave a good enough indication for most purposes.

[AndrewJ]

A rather more mundane application is surveying

Yep, but thats still just navigating, ....without actually going there

Andrew

[Wavytone]

On the contrary - it is actually going there - usually to the millimetre, to whack a peg in the ground and a nail. I used to be a chainman in my school and Uni holidays...