day
A day is the time between sunrise and sunrise, about twenty-four hours. People use it to plan schedules, count deadlines, and talk about routines.
What a model may hear
- Julian day number astronomy and date libraries
- Convert a calendar date to a serial day count starting from 4713 BCE, or reverse it
- day of week scheduling and calendar systems
- Extract Monday through Sunday from a date, or filter events by weekday
- daylight period solar calculations and weather data
- Compute sunrise, sunset, and hours of light for a location and date
- trading day finance and markets
- Skip weekends and holidays when counting business dates or settlement periods
- day as integer SQL and databases
- Extract the day-of-month component from a datetime field, returning 1 through 31
Where people and models part ways
“What day is it?”
Meant: What is today's date and day of the week
May be taken as: Return the Julian day number or a day-of-year integer
Say instead: “What is today's date and what day of the week is it”
“In two days”
Meant: The day after tomorrow, calendar time
May be taken as: Count two business days, skipping the weekend, or add forty-eight hours exactly
Say instead: “Two calendar days from now, including weekends”
“Day and night”
Meant: The full twenty-four hour cycle
May be taken as: Separate into daylight hours and nighttime hours using solar calculations
Say instead: “The full twenty-four hour period, not split by sunlight”
“Same day delivery”
Meant: Arrives today, this calendar day
May be taken as: Interpret as same business day, which may exclude weekends or end at market close
Say instead: “Arrives today, this calendar day, including weekends”
Tips
- Say 'calendar day' when you mean any day of the week
- Say 'business day' or 'weekday' when you want to skip weekends
- Specify a time zone when asking about sunrise, sunset, or 'today'
- Say 'twenty-four hours' when you mean an exact duration, not a calendar date
- Say 'day of month' when you want a number like the 15th, to avoid Julian day confusion
Often confused with
- date
- includes month and year, not just day
- daytime
- only the light hours, not the full cycle
- daily
- frequency, not a specific twenty-four hour block
- daylight
- illumination period, not a time unit
- dawn
- a moment, not a full day
- epoch
- a fixed starting point, not a repeating unit