Vernal Equinox

From the earliest times until today the vernal equinox was a reference point for position data. It can be dertermined in a relatively easy way at any place due to the point of sunrise on the eastern horizont and the point of sunset on the western horizont define a line straight through the oberserver's position on that day. Prehistoric observatories (e.g. Stonehenge) are orientated towards the vernal equinox. Depending on the world picture the vernal equinox defines a point on the horizont, on the sun's orbit or on the earth's orbit. The peculiarities of the coordinate systems are caused by these differences in the point of view.

vernal equinox