At Estevan, Saskatchewan, the latest sunrise time is at 9:12am on Dec 21. The earliest sunrise time is 3:12pm on June 21. Sunrise times on other dates can be predicted from a sinusoidal equation. There is no daylight saving time in Saskatchewan and the period is 365 days. Convert the time into minutes and the date into days. That is, June 21 is 172 days and Dec 21 is 355. The equation is given by D=180cos(2*pi*(t-10)/365)+372 where D=days and t=time Does anyone know why the phase shift is equal to 10?