The March equinox would occur on the same day every year if the Earth took exactly 365 days to make a complete revolution around the Sun. ... This means that each March equinox occurs about 6 hours later than the previous year's March equinox. This is why the date of the equinox can change from year to year.

Is the equinox always on the 21st?

Most years, this happens on either Sept. 22 or 23. However, every once in a while, the autumn equinox can occur on Sept. 21 or 24.

Are the equinoxes the same everywhere?

The equinox is being celebrated around the world - heralding autumn in the northern hemisphere and spring in the south. ... The autumn equinox in the northern hemisphere (it's the spring equinox for the southern hemisphere) always falls on 22, 23 or 24 September.