This animation illustrates the basic concepts of the Hindu lunisolar calendar.
I have modeled the elliptical orbits of the Sun and the Moon using actual parameters, scaled to fit the model. Switch to the spreadsheet view to see these parameters. I have scaled the Sun much more than the Moon so as to make both visible on the model (if I use the same scaling factor for both, the Moon simply disappears). The major axis of the Sun and the Moon are aligned with the X-Axis with their perigees placed on the positive direction. I even have programmed the ability to swivel the Moon major axis around the Earth, but have hidden that.
I have used the Newton method for solving the Kepler equation to find the Eccentric Anomalies of the Sun and the Moon. Since the animation proceeds sequentially, I take the previous eccentric anomaly and iterate the Newton algorithm twice to find the next eccentric anomaly.
By such modelling the concept of Adhika Tithi and Kshaya Tithi can now be illustrated by carefully stepping through the model.
Though the elliptical orbits of the Sun and the Moon are modeled, the actual orbital velocity is not modeled by the animation. The animation linearly steps through the Days one by one but the angles traverse by the Sun and the moon during a day are modeled accurately due to my modeling their elliptical orbits using actual parameters.
