Which Iranian university's institute calculates the exact moment of the vernal equinox for Nowruz?

The University of Tehran's Institute of Geophysics calculates the exact moment of the vernal equinox used for Nowruz.

Iran's Solar Hijri calendar is an astronomical calendar whose year begins around the Northern Hemisphere's spring equinox. The Institute of Geophysics, established as part of Tehran University in 1957, directs Iran's national calendar and provides the astronomical calculations behind the year's beginning.

The equinox itself is a precise instant, not merely a whole day. Under the Iranian calendar's rule, the relationship between that instant and Tehran's local time helps determine which civil day is designated as 1 Farvardin and Nowruz. This is why Nowruz can fall on different Gregorian dates, generally March 20 or March 21, rather than being permanently fixed to one date.

The institute is often confused with an entire university or with Iran's general scientific institutions. The canonical answer is specifically the Institute of Geophysics associated with the University of Tehran. The calculation also helps explain why the Solar Hijri calendar is exceptionally well aligned with the seasons compared with calendars using a simpler fixed leap-year pattern.