Norouz, the Persian New Year, which starts precisely at the vernal equinox was at 1:11 a.m. on Mar. 20 this year. “It’s the most important holiday of the year,’’ says Melisa Jalilian, 27, who immigrated to Watertown from Tehran, the capital of Iran, with her family in 2004. “It’s a time when people are positive, and feel hopeful, because it’s spring, and everything feels new,’’ she says. Norouz is also celebrated by Turks, Kurds, Albanians, Azeris, Uzbeks, Tajiks, and other ethnic groups. In Iran, the festivities go on for 13 days, and everyone gets the time off. Families renew traditions, visit friends and relatives, and indulge in dishes infused with ingredients evoking spring.