Mac Oglesby wrote: > > Both Mayall (p.244) and Rohr (p.91) give the formula for finding the hour > angle of the sun at sunset or sunrise as > > cos HA = tan L tan D > > where HA is the hour angle in degrees of the sun at its rising or setting, > L is the latitude of the place, and D is the declination of the sun. > > When I run a latitude of 43 and a declination of -23.44 through my > calculator or on a computer spreadsheet, I get a result of 113.8478 for the > hour angle! A declination of 0 (with the same latitude) gives an hour > angle of 90, which looks good, but 23.44 yields an hour angle of 66.1522 > degrees! > > A friend has suggested that the formula should be corrected to read > > cos HA = - tan L tan D > > and that there is a misprint in both books. Has anyone else noticed this? > > Mac Oglesby
Mac, The formula to calculate the 'half of the daylength' T is cos T = - tan lat * tan delta. Then sunrise is at - T and sunset is at + T. lat is latitude, pos. in northern hemisphere, neg. in southern. delta is suns declination, pos. if sun in nothern hemisphere and so on. hourangle neg. in the morning, pos. in the afternoon. Fer J. de Vries.
