Hi!

I am trying to get perl to figure out where in the sky certain objects (Planets, spaceship, maybe stars) are, so i can point a servo-controlled laser pointer there.

I am completely ignorant of the finer things of astronomy, my problem might be that i simply didnt 'grok' some very basic issues.

Anyhow: I figure i need the Azimuth and Elevation of the object I want to point at, for my current location (San Jose, Costa Rica). There seems to be another more 'professional' coordinate system for these kind of things that gives me the position in Radians and Declination, which I dont quite understand, but AFAICT dont really need, because I want to point my laser using stuff like "point to 234 degrees North, and 45 degrees over the horizon".

My basic test code is the following:
use Astro::Coords;
use Astro::Telescope;
use Time::Piece;

my $time = new Time::Piece;


# adjust for time zone??
# $time += 6*3600;

$c = new Astro::Coords( planet => 'mars' );

# 9.956318, -83.995503, 1480m

$c->telescope( new Astro::Telescope( Name => 'MvS', Long => -83.995503
+, Lat => 9.956318, Alt => 1480 ));

$c->datetime( $time );

$az = $c->az( format => 'd' );
$el = $c->el( format => 'd' );
$ra = $c->ra( format => 'd' );
$dec = $c->dec( format => 'd' );
print "az: $az\nel: $el\n\nra: $ra\ndec: $dec\n";

[download]
Which, at this very moment spits out: 
C:\Users\schweini\Dropbox\hacks>perl laserTelescope.pl
az: 64.4509897905136
el: 2.92864468337563

ra: 251.654925187611
dec: -23.3814670583575

[download]
Which, checking against Google Sky Map on my android phone, is completely off. (Mars seems to be quite high in the sky right now, here where I am located).

If I look it up using NASA's 'Horizon' webservice, I get:

**********************************************************************
+*********************************************************************
+*******************************************************
 Date__(UT)__HR:MN     R.A._(J2000.0)_DEC. X_(sat-primary)_Y SatPANG  
+APmag  S-brt Ob-lon Ob-lat            delta      deldot   1-way_LT   
+ S-O-T /r    S-T-O   PsAng   PsAMV N.Pole-RA  N.Pole-DC
**********************************************************************
+*********************************************************************
+*******************************************************
$$SOE
 2012-Oct-25 00:00 Nm  251.06257 -23.30814 145863.8 -40206.8 111.721  
+ 1.24   4.23 170.57   5.54 2.03255620848271   6.3552294  16.904255  4
+0.8647 /T  26.9310    n.a.    n.a. 317.66783   52.87870
 2012-Oct-25 01:00  m  251.09522 -23.31220 145830.0 -40170.2 111.714  
+ 1.24   4.23 185.16   5.53 2.03270971936605   6.3981098  16.905531  4
+0.8533 /T  26.9252    n.a.    n.a. 317.66783   52.87870
 2012-Oct-25 02:00  m  251.12797 -23.31625 145795.9 -40133.5 111.706  
+ 1.24   4.23 199.75   5.51 2.03286393613495   6.4135372  16.906814  4
+0.8419 /T  26.9193    n.a.    n.a. 317.66783   52.87870
 2012-Oct-25 03:00  m  251.16081 -23.32029 145761.6 -40096.7 111.698  
+ 1.24   4.23 214.35   5.50 2.03301818013345   6.4003399  16.908097  4
+0.8304 /T  26.9134    n.a.    n.a. 317.66783   52.87870
 2012-Oct-25 04:00  m  251.19373 -23.32433 145727.3 -40059.8 111.691  
+ 1.24   4.23 228.94   5.49 2.03317176798120   6.3592992  16.909374  4
+0.8189 /T  26.9074    n.a.    n.a. 317.66783   52.87870
 2012-Oct-25 05:00  m  251.22674 -23.32838 145693.0 -40022.9 111.683  
+ 1.24   4.23 243.53   5.47 2.03332405819567   6.2930959  16.910641  4
+0.8074 /T  26.9013    n.a.    n.a. 317.66783   52.87870
 2012-Oct-25 06:00  m  251.25982 -23.33244 145658.8 -39985.9 111.675  
+ 1.24   4.22 258.12   5.46 2.03347449495092   6.2061269  16.911892  4
+0.7959 /T  26.8951    n.a.    n.a. 317.66783   52.87870
 2012-Oct-25 07:00  m  251.29295 -23.33653 145624.9 -39948.8 111.667  
+ 1.24   4.22 272.72   5.45 2.03362264598894   6.1042058  16.913124  4
+0.7845 /T  26.8889    n.a.    n.a. 317.66783   52.87870
 2012-Oct-25 08:00  m  251.32610 -23.34064 145591.3 -39911.8 111.660  
+ 1.24   4.22 287.31   5.43 2.03376823209864   5.9941654  16.914335  4
+0.7731 /T  26.8827    n.a.    n.a. 317.66783   52.87870
 2012-Oct-25 09:00     251.35927 -23.34478 145558.1 -39874.7 111.652  
+ 1.24   4.23 301.90   5.42 2.03391114615311   5.8833922  16.915523  4
+0.7619 /T  26.8764    n.a.    n.a. 317.66783   52.87870
 2012-Oct-25 10:00     251.39241 -23.34894 145525.2 -39837.7 111.644  
+ 1.24   4.23 316.49   5.40 2.03405146040802   5.7793223  16.916690  4
+0.7508 /T  26.8702    n.a.    n.a. 317.66783   52.87870
 2012-Oct-25 11:00 N   251.42552 -23.35312 145492.8 -39800.7 111.636  
+ 1.24   4.23 331.09   5.39 2.03418942156454   5.6889341  16.917838  4
+0.7397 /T  26.8640    n.a.    n.a. 317.66783   52.87870
 2012-Oct-25 12:00 *   251.45857 -23.35732 145460.8 -39763.8 111.628  
+ 1.24   4.23 345.68   5.38 2.03432543393411   5.6182727  16.918969  4
+0.7288 /T  26.8578    n.a.    n.a. 317.66783   52.87870
 2012-Oct-25 13:00 *   251.49155 -23.36153 145429.1 -39727.0 111.620  
+ 1.24   4.23   0.27   5.36 2.03446003185360   5.5720371  16.920088  4
+0.7180 /T  26.8517    n.a.    n.a. 317.66783   52.87870
 2012-Oct-25 14:00 *   251.52445 -23.36574 145397.6 -39690.3 111.612  
+ 1.24   4.23  14.86   5.35 2.03459384323222   5.5532601  16.921201  4
+0.7073 /T  26.8457    n.a.    n.a. 317.66783   52.87870
 2012-Oct-25 15:00 *   251.55727 -23.36994 145366.3 -39653.7 111.605  
+ 1.24   4.23  29.46   5.34 2.03472754671638   5.5631014  16.922313  4
+0.6966 /T  26.8397    n.a.    n.a. 317.66783   52.87869
 2012-Oct-25 16:00 *   251.59001 -23.37414 145335.1 -39617.1 111.597  
+ 1.24   4.23  44.05   5.32 2.03486182539373   5.6007684  16.923430  4
+0.6859 /T  26.8339    n.a.    n.a. 317.66783   52.87869
 2012-Oct-25 17:00 *   251.62267 -23.37831 145303.8 -39580.6 111.589  
+ 1.24   4.22  58.64   5.31 2.03499732019437   5.6635701  16.924557  4
+0.6752 /T  26.8281    n.a.    n.a. 317.66783   52.87869
 2012-Oct-25 18:00 *   251.65527 -23.38245 145272.4 -39544.2 111.581  
+ 1.24   4.22  73.23   5.30 2.03513458616844   5.7471012  16.925698  4
+0.6645 /T  26.8223    n.a.    n.a. 317.66783   52.87869
 2012-Oct-25 19:00 *   251.68784 -23.38655 145240.7 -39507.7 111.573  
+ 1.24   4.22  87.83   5.28 2.03527405462362   5.8455422  16.926858  4
+0.6537 /T  26.8166    n.a.    n.a. 317.66783   52.87869

[download]

So, the results perl give me correspond to 18:00 UTC time (I am 6 timezones away from UTC), even though I am telling Astro::Coords where exactly I am located, so I figure that it should tell me where Mars is RIGHT NOW. (My locale seems to be set up correctly, too - so i would hope Time::Piece takes that into account?).

If i SUBTRACT(!??!) 6 hours (6*3600) of my Time::Piece, i get a location info for Mars that seems to roughly correspond to what Google Sky Map is telling me - but then Neptune is way off, so that crude correction-measure doesnt work. Adding 6 hours seems even worse.

Long story short: what am i doing wrong? How can i somehow look up the Azimuth and Elevation of celestial objects at my current position and time?

I was also thinking about hooking myself into that Horizons webservice and somehow (how??) convert those esoteric RaDec coordinates to simple earth-based AzEl coordinates, but i dont know how.

Thanks for any help,

M.

In reply to Locationg celestial objects (using Astro::Coords, if need be) by schweini

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