Question

autumn Equinox is observed on what

Answer 1

Autumn equinox is observed on 23 September in northern hemisphere and on 21 March in southern hemisphere.
Hope it helps.

Answer 2

${ \color{magenta}{ \underline{ \underbrace{ \huge{ \mathrm{Answer}}}}}}$

On 21st March and September 23rd, direct rays of the sun fall on the equator. At this position, neither of the poles is tilted towards the sun. So, the whole earth experiences equal days and equal nights. This is called an equinox.

▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬