I want to calculate the sunrise, sunset and daylength for 365 days. Therefore I use the insol package. The package includes the daylength() function to achieve this. The function takes latitude, longitude, day and timezone as inputs. The JD() function is used for transforming a POSIXct object into a Julian Day as required by the daylength() function.

Reproduceable example:

date <- as.POSIXct("2021-01-15")
date_sunevents <- daylength(48.457778, 9.00, insol::JD(date), 1)

This codes returns the following values for the given day:

• sunrise: 8.28
• sunset: 16.83
• daylength: 8.55

This values seem to be close to the real values but something is wrong with the format. I expected the values to be in a format between 0-24.0-59. I feel like I am missing the point of the function..

CodePudding user response：

Answer from ChatGPT

The values that the daylength() function returns are not in a time format, but in decimal hours. The sunrise value of 8.28 indicates that the sun rises at 8:16:48 (8 hours 16 minutes 48 seconds) on that day. Similarly, the sunset value of 16.83 indicates that the sun sets at 16:49:48 (16 hours 49 minutes 48 seconds) on that day. The daylength value of 8.55 indicates that the day is 8 hours and 33 minutes long.