You need to check to see how your client wants to represent the day of week. This function returns 0 for Sundays. ISO 8601 uses 7 for Sundays.BTW, You can also calculate the day of week with modular division:$dow = (1 + $julianday) % 7; // returns 0 for Sundays.$dow = ($julianday % 7) + 1; // returns 7 for Sundays.https://en.wikipedia.org/wiki/Julian_day#Finding_day_of_week_given_Julian_day_numberTo make matters confusing. The Julian Date starts at noon UTC. Some programs such as SQLITE3 use real numbers to record date and time. If you pass this function a float; it will return a different day of week for the morning than for the afternoon.When given a julianday with a decimal part you will need to add a half day and may need further adjustment for your timezone.