In #China, New Year's Day falls in spring, but the exact date is determined by when the new moon falls in relation to #Dongzhi, the winter solstice festival.
The #RigVeda also implies that the winter solstice marked New Year's Day in the #IndusValley civilisation, but is unfortunately too vague to say much with certainty.
I am now going to talk in a somewhat more abstract and philosophical way about time, drawing on #Jyotisha
6/11
All this time I thought that the sun's angular velocity along the epicycle was measured relative to a line from Earth the the sun's apogee (taking the anomalistic orbit as the reference frame, rather than the #zodiac or the #ecliptic), but it turns out it's actually measured relative to a line joining the centre of Earth to the centre of the sun.
The #SuryaSiddhanta's methods for calculating the positions of the sun and moon at times specify that the absolute value of the jya of an arc must be added to some value in some cases, and subtracted in others.
Since the jya is the predecessor to the modern sine, in this we see the earliest inklings of negative values of trigonometric functions. It's interesting how ideas develop.
Infrapink (he/his/him)