According to Yasna and Vispered, the 2 most sacred and ancient parts of the Avesta, the beginning of the New Zoroastrian Year is Vernal equinox, “hamas.path. maiðya” or “hamaß .path. maiðya” in Avestan.
The Avestan term refers specifically to the moment when the center/middle position (maiðya ) of the Sun is in the same/equal (hama) position/passage/path (Avestan Path) as the Earth’s midway line. It is specific to the moment when such a passage happens and when the celestial points/paths of intersection are at an equal/same length (hama) from each other, hence Equinox.
Spring Equinox is the celebration of a splendid new dawn and new light or “nauv-rooz,” the springing up of new hope and new life. It is a union with triumphant spring and powers of new light and growth, a time for flowering plants, fruitful vines, and fertility in man and the universe. It is about the triumph of the bright and auspicious spirit and the wondrous adventures of life.
Spring Equinox is also the start of the astrological year. Zoroastrian or Ancient Iranian New Year has much in common with Ôstara spring celebrations of the ancient Germanic tribes.
Ôstara is the spirit of new light, the glorious rising sun and radiant fresh dawn that brings much joy, happiness, and new bursting life energy. In fact, the concept and meaning behind Ôstara is the same as Avestan úshtá.
The 19th century scholar Jacob Grimm traced the name to a Proto-Indo-European goddess of the dawn Ausṓs, from which descends the common Germanic goddess of new dawn Ôstara, Greek Eós and Vedic úshás.
Also, the original Roman calendar called “Romulus” started with the Spring Equinox. The names of months such Septembris from septem September meaning the 7th month; Octobris from octo meaning October or the 8th month; Novembris from novem meaning November or the 9th month; and Decembris from decem meaning December or the 10th are reminders that the year once started with the renewal of Spring.
The beautiful Bonfires before Spring Equinox and other pleasant rituals of the Zoroastrians such as dances of joy and three joyful leaps around the fire, the holy and healing spring water drawn on the first dawn after the Spring Equinox, all have parallels in other ancient Indo-European traditions.
And let us not forget the importance of painted or colored eggs. The sculptures on the walls of Persepolis show people carrying eggs for Nauv-rooz celebrations and gift-giving. For to give the gift of a painted or colored egg, is to give a gift of renewed life. That is why the egg must be whole and colorful.
Similar and even more elaborate rituals exist among the Ukrainians. The pysanka eggs symbolically assure good fortunate life and protection. The word comes from the verb pysaty, “to write.” (Compare pysaty with middle Iranian ni-pyshtan, Farsi ni-vyshtan, “to write down.”)
Spring Equinox is about the re-making of a new world, into wonder and fresh, new adventure and that is why it marks the beginning of the Zoroastrian New Year.
ardeshir
Authentic Gatha Zoroastrianism 
Very Good this article. At least the Ukrainian part seems accurate! Well Done!