What is the name of the point in space where the Sun appears to cross the celestial equator from N to S?

Question

On what date does the Sun appear to cross the point on the celestial equator?

Answer 1

That's the autumnal equinox.  It occurs around September 22nd.

Answer 2

Autumnal equinox for us northern hemisphere residents, or the vernal equinox for those in the southern hemisphere.  It occurs this year on Sept. 22 at 15:39 universal time.