Re: Where is Azimuth = 0?

Alphonse POUPLIER (
Wed, 23 Apr 1997 00:09:59 +0200 (MET DST)

>No, the overwhelming majority of astronomy texts (I've checked a couple
>of dozen today) appear to use N=0. One notable exception is Jean Meeus,
>the Belgian astronomer who is the guru of computational astronomy and
>the author of the book "Astronomical Algorithms". He uses S=0,
>supporting this by quoting from a 19th Century text by William Chauvenet
>and another by A Danjon in 1959. As I say, I could quote many more
>contrary authorities, including the "Explanatory Supplement to the
>Astronomical Almanac" which states unequivocally that "Azimuth is
>measured in the plane of the horizon from the north, increasing in
>positive value towards the east."
>I note that N=0 for azimuth is also the convention in Quicksat.
> Alan Pickup | COSPAR site 2707:  55d53m48.7s N   3d11m51.2s W  156m asl

My friend Jean Meeus explains very well in his book (hereabove mentionned)
why he prefers azimuth = 0 to be south.
Be I can't agree with him:
1) The IAU (International Astronomical Union) recommends the use
   of azimuth from 0 to 360 deg. (0 being North and 90 being East)
2) At my knowledge, only FRENCH and OLD asronomers still use
   azimuth from 0 to + or -180 deg. (0 being South, East negative, West
   All other people use the recommended system.
Note: Jean Meeus tells how to do to get azimuth 0 = North.
In my astronomical programs, I give the possibility to use both systems
but in my programs concerning the artificial satellites, I use only
the recommended system.

My pleasure, avec plaisir,  Alphonse
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