How do we know about precession?

1 Answer
Jul 21, 2016

Slight displacement of equinox location and its little later occurrence, over years..


The Biannual Equinox event ( about March 21 and about September

23 ) occurs at a location on the equator, twice in a year. The noon

Sun is right over head there ( somewhere near New Papua Guinea

Island, South of Indonesia, for March 21 vernal equinox ), at

that instant.

Noticeably, this instant and location change over centuries.

It is estimated that, longitudinally, this location makes one round

upon the equator, in about 258 centuries (Great Year)

The corresponding event at other latitudes relates to minimum

noon-shadow ( against no shadow at equinox ), at the same noon.

and longitude.