C'mon pretty, you still got it.

"Persians celebrate the new year marking the first day of spring with some variation of day based on the vernal equinox." I looked at this a little later and tried to read it, it made no sense, read poorly and in general just... Yuck. So, lets's try again. so, here it is.
Persians celebrate the new year by marking the first day of spring. There is some variation of the day chosen for celebration, based on where the vernal equinox lands. See, this year is a good example, the first day of spring is considered to be March 21st. However, the vernal equinox landed on the 20th at something like 5:08pm. So the new years day can be either the 20th ,21st or the 22nd. the celebrations usualy last for thirteen days and involve everything from cleaning to throwing sprouts in the river or untying knots in handkerchiefs.
Anyway, I hope that adds some clarity.