I have found a mistake in the first edition of Astronomical Algorithms. In Chapter 12, "Transformation of Coordinates", there is an unnumbered equation, just after Eq. 12.6. Transformation from horizontal into equatorial coordinates: sin A tan H = ---------------------------------- cos A cos(phi) + tan h cos phi This should really be: sin A tan H = ---------------------------------- cos A sin(phi) + tan h cos phi ^^^ ^^^ ^^^ An examination of 12.1, 12.3 and especially 12.5 is revealing. You might want to mark up your copy so you won't fall into the same trap that I did. Someone with the second edition will have to tell us if the mistake is there too. Does anyone know of any other mistakes in AA? Randy ----------------------------------------------------------------- Unsubscribe from SeeSat-L by sending a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@lists.satellite.eu.org http://www2.satellite.eu.org/seesat/seesatindex.html