Copyright 2023 Daniel Kalak
Licensed under CC-BY-ND-4.0

We can distinguish 4 kinds of day:

* A calendar day begins at midnight.

* When I stay up past midnight, I define
  the new day to start at sunrise.

* An astronomical day begins at noon.

* A liturgical day (in Abrahamic
  religions) begins at sunset.

Notice also how the seasons of the years
and their boundaries resemble the times of
day and their boundaries:

 day             | year
 ----------------|-----------------------
 00:00 midnight  | 12-21 winter solstice
       night     |       winter
 06:00 sunrise   | 03-21 vernal equinox
       morning   |       spring
 12:00 noon      | 06-21 summer solstice
       afternoon |       summer
 18:00 sunset    | 09-23 autumnal equinox
       evening   |       autumn

This similarity is extreme at the poles,
where a solar day takes an entire year.

The game "Nirvana", which you can find in
my download section, hints at this
similarity and widens it to include
different stages in life.