# Approximate sunrise and sunset times

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This function is not perfect, but it does a reasonable job estimating sunrise and sunset times for my field site. If more accurate data are required, try here. Note, the command to calculate day of year is: strptime(x, “%m/%d/%Y”)$yday+1**Quantitative Ecology**, and kindly contributed to R-bloggers]. (You can report issue about the content on this page here)Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.

suncalc<-function(d,Lat=48.1442,Long=-122.7551){ ## d is the day of year ## Lat is latitude in decimal degrees ## Long is longitude in decimal degrees (negative == West) ##This method is copied from: ##Teets, D.A. 2003. Predicting sunrise and sunset times. ## The College Mathematics Journal 34(4):317-321. ## At the default location the estimates of sunrise and sunset are within ## seven minutes of the correct times (http://aa.usno.navy.mil/data/docs/RS_OneYear.php) ## with a mean of 2.4 minutes error. ## Function to convert degrees to radians rad<-function(x)pi*x/180 ##Radius of the earth (km) R=6378 ##Radians between the xy-plane and the ecliptic plane epsilon=rad(23.45) ##Convert observer's latitude to radians L=rad(Lat) ## Calculate offset of sunrise based on longitude (min) ## If Long is negative, then the mod represents degrees West of ## a standard time meridian, so timing of sunrise and sunset should ## be made later. timezone = -4*(abs(Long)%%15)*sign(Long) ## The earth's mean distance from the sun (km) r = 149598000 theta = 2*pi/365.25*(d-80) z.s = r*sin(theta)*sin(epsilon) r.p = sqrt(r^2-z.s^2) t0 = 1440/(2*pi)*acos((R-z.s*sin(L))/(r.p*cos(L))) ##a kludge adjustment for the radius of the sun that = t0+5 ## Adjust "noon" for the fact that the earth's orbit is not circular: n = 720-10*sin(4*pi*(d-80)/365.25)+8*sin(2*pi*d/365.25) ## now sunrise and sunset are: sunrise = (n-that+timezone)/60 sunset = (n+that+timezone)/60 return(list("sunrise" = sunrise,"sunset" = sunset)) }

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