| EQ2HOR discrepancy -- longitude interpretation? [message #70314] |
Mon, 29 March 2010 09:03 |
Josh Von Korff
Messages: 1
Registered: March 2010
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Junior Member |
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EQ2HOR is supposed to convert (RA, dec) to (azimuth, elevation.)
It disagrees with my hand calculation and
http://home.att.net/~srschmitt/script_celestial2horizon.html ,
as well as common sense, see below for the code. (It gives a negative
altitude for some coordinates that I believe to be valid.)
However, when I change the longitude from -66.75 to +66.75, EQ2HOR
agrees with
http://home.att.net/~srschmitt/script_celestial2horizon.html
for all inputs I have tried, as long as the former uses +66.75 and the
latter uses -66.75.
My telescope is in Puerto Rico, at 66.75 degrees West longitude.
But the online guide clearly states:
"lon : EAST longitude of location in degrees (Specify west longitude
with a negative sign.)"
(See http://idlastro.gsfc.nasa.gov/ftp/pro/astro/eq2hor.pro)
What am I doing wrong?
IDL> eq2hor, 5.577 * 15, 22.02, 2454989.152131d, alt, az, $
IDL> lat = 18.35, lon = -66.75, altitude=497.0, $
IDL> precess_ = 0, nutate_ = 0, aberration_ = 0, refract_ = 0, /verb
Latitude = +18 21 0.0 Longitude = -66 45 0.0
Julian Date = 2454989.152131
Ra, Dec: 05 34 37.2 +22 01 12.0 (J2000)
Ra, Dec: 05 34 37.2 +22 01 12.0 (J2009.4296)
Ra, Dec: 05 34 37.2 +22 01 12.0 (fully corrected)
LMST = +13 06 47.3
LAST = +13 06 48.2
Hour Angle = +07 32 11.0 (hh:mm:ss)
Az, El = 19 55 26.1 -13 05 11.0 (Apparent Coords)
Az, El = 19 55 26.1 -13 05 11.0 (Observer Coords)
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