day
Let an agent distinguish the day as a unit of time, as a solar period and as a calendar date, and handle time zones and daylight saving correctly.
Research draft, second pass
A second pass drafted this model: the structure a model of this thing needs, and what is known about it in the world. The line under this one says how the second half was obtained - researched against sources, or recalled without web access, in which case nothing here was read anywhere and every claim is a lead to verify. Unreviewed either way.
written by Claude from model knowledge without web access - no source was read, every claim is a lead to verify
Researched by: Claude
Purpose and description
Let an agent distinguish the day as a unit of time, as a solar period and as a calendar date, and handle time zones and daylight saving correctly.
A unit of time of 86,400 seconds, and the period of one rotation of the Earth relative to the Sun, reckoned from midnight to midnight in civil use.
What it is for: Organising time for daily life, work, law and science.
It can be count days, for durations and deadlines; name days, with calendar dates and weekdays; divide days, into hours, minutes and seconds; adjust them, as with leap seconds and daylight saving shifts.
Distinguishing features
A unit of time and a solar cycle, which differ slightly
The civil day follows a time zone and can be 23 or 25 hours on daylight saving changes
Distinct from daytime, the light part of the day
A calendar date names a particular day
What it looks like
Experienced as daylight and night; recorded on clocks and calendars.
Physical character
length: 86400 s - SI day; mean solar day varies by milliseconds
sidereal day: 86164.09 s - rotation relative to the stars
How it is recognised
Sunrise and sunset mark daylight, not the civil day
Calendars show days as dates and weekdays
Clocks reset at midnight in civil time
Related models
is a kind of - accepted for use with the SI
is named by - a date identifies one day
is divided into - 24 hours in civil time
is confused with - daylight is only part of the day
In practice
Families and kinds
solar day, sidereal day, civil day
working day, business day, calendar day
by name: weekdays
Identifiers
unit symbol d accepted for use with the SI
Standards and regulation
SI Brochure, non-SI units accepted for use
ISO 8601 for date and time representation
National laws on time zones and daylight saving
Failure modes and hazards
Assuming every day has 24 hours across daylight saving changes
Confusing calendar days with business days in deadlines
Time zone errors that move events to another day
Where this came from
wikidata · CC0 1.0
Also registered as vr.tr.day-6
Drafted structure
Bundle to layer to finding to question, as the second pass will find it: 4 bundles · 8 layers · 8 findings · 16 questions.
Unit and astronomy The day as unit and as rotation.
The unit and the astronomical day differ; precision work needs the distinction.
Unit
Definition in seconds.
Unit definition
The unit and its relation to SI.
- Which definition of day applies here? definition
- Does the precision required make the difference matter? boundary
Astronomical day
Solar and sidereal days.
Astronomical basis
The astronomical day used.
- Is the solar or the sidereal day meant? definition
- How does day length vary over the year? measurement
Civil day Days in time zones.
The civil day is political: governments set time zones and daylight saving.
Time zone
The zone the day belongs to.
Zone rules
The zone and its offset rules.
- In which time zone is this day reckoned? definition
- Does a daylight saving change fall on it? boundary
Day boundaries
Midnight and edge cases.
Boundary rules
When the day begins and ends.
- When does this day begin and end? definition
- How are events near midnight assigned? action
Counting days Durations and deadlines.
Counting days in law and business follows rules that differ from simple arithmetic.
Durations
Calendar and business days.
Counting rule
Which days are counted.
- Are calendar days or business days counted? definition
- Which holidays are excluded, and in which jurisdiction? boundary
Deadlines
Day-based deadlines.
Deadline rule
How a day-count deadline is computed.
- How is this deadline computed in days? definition
- What happens when it falls on a non-working day? boundary
Naming Weekdays and dates.
Days are named in several ways at once.
Weekday
The day of the week.
Weekday naming
The weekday and numbering convention.
- Which weekday is this, and which numbering convention applies? definition
- Does the week start on Monday or Sunday here? boundary
Date
The calendar date.
Date identifier
The date naming this day.
- Which calendar date names this day? definition
- In which calendar? definition
What the second pass must settle
- Should the civil day and the solar day be separate entries?
- How should business days be modelled across jurisdictions with different holidays?
- How should agents present day counts that cross time zones?