Function gregorianToJdn

gregorianToJdn(
    year: number,
    month: number,
    day: number,
    hour?: number,
    minute?: number,
    second?: number,
    timezoneOffset?: number,
): number
Convert a proleptic Gregorian date to a Julian Day Number (JDN).

This is the standard continuous day count used by modern astronomers (starting from Jan 1, 4713 BCE).
Parameters
- year: number
  Proleptic Gregorian year
- month: number
  Month (1-12)
- day: number
  Day (1-31)
- hour: number = 12
  Hour (0-23)
- minute: number = 0
  Minute (0-59)
- second: number = 0
  Second (0-59)
- timezoneOffset: number = 0.0
  Offset from UTC in hours (e.g., +5.75 for Kathmandu)
Returns number
Julian Day Number as a decimal.