Don't mean to overwhelm you with pings, only a bit of clarification/explanation:
Norooz is, and has always been, a National celebration in Iran, for all Iranians, regardless of ethnicity or faith. Throughout history, Iranians have continued to celebrate Norooz under Arab, Turk and Monghol occupation.
Those of the Iranian (Iranic) stock in Tajikistan, Republic of Azarbaijan, Afghanistan as well as those in Central, and South Asia, Northwestern China, the Caucasus, the Crimea, and the Balkans also celebrate NoRooz. They each have their own minor variations of related rituals, traditions, food, etc..
No-Rooz (literally meaning "New Day" in Persian language) is only a religious celebration for Zoroastrians. More so because Zoroaster's b/day is on March 26, which coincides w/ 13 day long Norooz celebrations. Though Zoroastrians also have a separate "religious" calendar. Actually, the Parsi's (Zoroastrian community in India) use yet another Zoroastrian calendar (warrants having a separate thread on this topic alone).
Iranian (Persian) national calendar (and months) is solar based, not lunar like the Islamic one. The Persian New Year (Norooz) has astronomical significance; it is not faith based. When the Sun crosses directly over the Earth’s equator, this moment is known as the vernal equinox in the Northern Hemisphere, hence the start of the Iranian New Year (Norooz).
and one of their great heroes is the Zoroastrian hero Rustom
MOST national heroes in Iran, even now, are considered as pre-Islamic.
Those who beat themselves black & blue mourning the death of their "hero" Hossein (the 3rd Shia Imam) are Not the majority in Iran. But, because they get most of the publicity by western & arab media outside Iran, we in the West think that's the majority of the Iranian population. It is very much a misleading portrayal of the majority of Iran & Iranians in Iran. More so since the Khomeinist regime took over & has tried to further Arabize & Islamize Iran.
Also, since Khomeinist regime came to power, on several occasions, over the past 32 yrs, the mullahs' regime has tried to ban Norooz & other non-Islamic (pre-Islamic) national celebrations in Iran. But, they've been unsuccessful due peoples' resistance & visible objections.