R: Daylength

daylength {geosphere} | R Documentation

## Daylength

### Description

Compute daylength (photoperiod) for a latitude and date.

### Usage

    daylength(lat, doy)

### Arguments

`lat` | latitude, in degrees. I.e. between -90.0 and 90.0
`doy` | Interger, day of the year (1..365) for leap years; or an object of class Date; or a character that can be coerced into a date, using 'yyyy-mm-dd' format, e.g. '1982-11-23'

### Value

Daylength in hours

### Author(s)

Robert J. Hijmans

### References

Forsythe, William C., Edward J. Rykiel Jr., Randal S. Stahl, Hsin-i Wu and Robert M. Schoolfield, 1995. A model comparison for daylength as a function of latitude and day of the year. Ecological Modeling 80:87-95.

### Examples

    daylength(-25, '2010-10-10')
    daylength(45, 1:365)

    # average monthly daylength
    dl <- daylength(45, 1:365)
    tapply(dl, rep(1:12, c(31,28,31,30,31,30,31,31,30,31,30,31)), mean)

[Package geosphere version 1.5-5 Index]