Starpath · Culture and history
True solar time
The clock is a convention; the sun is the reference.
Clock time is shared across a whole time zone, and daylight saving shifts it further. The sun, though, reaches its highest point at different moments across a zone: about four minutes later for every degree you go west.
The tilt of the Earth and its oval orbit add a seasonal drift of up to about a quarter of an hour, called the equation of time.
Many practitioners therefore convert the birth time to local true solar time before choosing the double-hour. Astravia does this when it knows your birthplace, and shows the corrections in the calculation notes.
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The correction matters most when a birth time falls close to the boundary between two double-hours. Far from a boundary, it changes nothing.