Write an equation into Javascript

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I need an equation that give the earth tilt of the current day. Max Tilt is 23.45 on 22 of June, min is -23.45 on 22 December. I've found this equation which should works but I can't write it into javascript.

δ=sin-1(sin(23.45°)sin(360365(d-81)))

d is the number of the day (1-365). Source : http://pveducation.org/pvcdrom/properties-of-sunlight/declination-angle

My try :

Math.pow(Math.sin(Math.sin(23.45) * (Math.sin((360/365) * (356 - 81)))), -1)

which gives -1.3140077301935487, whereas -23.45 is expected.

Any ideas what's wrong on my conversion ?

asked 35 secs ago

Spope

37

Write an equation into Javascript