I am trying to find the declination at the horizon in the east at a particular latitude. The equation is: delta = asin(sin(lat)*sin(Alt) - cos(lat)*cos(Alt)*cos(Azi)) where Azi is the azimuth and is equal to 90 degrees in the eastern most direction. Alt is the Altitude and is equal to 0 degrees at the horizon. From this equation delta is always equal to 0 but intuitively the horizon plane changes with the latitude. Could this equation be misinterpreted?