Moon tilt

[furiosFast]

Hi,
i've write this function for calculate the moon tilt illusion angle, according to this document: http://master.grad.hr/hdgg/kog_stranica/kog18/06myers-KoG18.pdf

static func moonTilt (date: NSDate, location: CLLocationCoordinate2D) -> (alfa: Double, beta: Double, diff: Double) {      

        let moonAltitude = moonPosition(date: date, location: location).altitude
        let moonAzimuth = moonPosition(date: date, location: location).azimuth
        let sunAltitude = sunPosition(date: date, location: location).altitude
        let sunAzimuth = sunPosition(date: date, location: location).azimuth

        let absAzimMoonSun = abs(sunAzimuth - moonAzimuth)
        let tanAlfa = ((cos(moonAltitude) * tan(sunAltitude)) - (sin(moonAltitude) * cos(absAzimMoonSun))) / sin(absAzimMoonSun)
        let tanBeta = (sin(moonAltitude) - sin(sunAltitude)) / (cos(sunAltitude) * sin(absAzimMoonSun))
        var diff = 0.0
        if (absAzimMoonSun * radiansToDegrees) <= 180 {
            diff = atan(-tanBeta)
        } else {
            diff = atan(tanAlfa)
        }

        return (tanAlfa, -tanBeta, diff)
    }

I use this code to rotate an image of the moon, but it presents a constant error when compared to sites like: https://www.timeanddate.com/astronomy/italy/turin
or
https://www.mooncalc.org/#/45.3502,7.744,13/2018.09.05/09:26/99/0

Can someone tell me what's wrong?