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
