Let us try to do a simple and straightforward astronomical dating of the actual vedic period.
One is the spring equinox and the other is the vernal equinox.
It is to be observed that in northern hemisphere what looks like a transition of sun from south to north i.e vernal equinox, actually looks like a transition from north to south when observed in the souther hemisphere.
There are also two other points of extremes of north and south which sun touches and comes back as it rises everyday, and these are called summer and winter solstices.
So over a period of time it looks as though sun is oscillating on either side of the due east during sun rise (or either side of due west on sunset)!
Note that what we consider as summer solstice in northern hemisphere is winter solstice in southern hemisphere.
Seasons on earth are due to the tilting of earth’s axis, and hence when there is summer in the northern hemisphere its winter in south and vice versa. During the vedic ages, new year began on vernal equinox and was called Agrahayana. The new year then was celebrated in the vedic month of Margashira (named after a star lambda orionis in the constellation of Orion).
Since there is also a precession of the earth’s axis, the equinox dates keep changing every year, and when seen from a stellar background the constellation in which the sun rises on the vernal equinox also keeps changing over a period of time.
In our times today, the sun rises in the background of Pisces (Meena Rashi) on the vernal equinox.
Whereas in the vedic period it used to rise in the background of Gemini (Margasira/Orion is in Gemini).
The earth’s precession takes about 25,800 years for one complete cycle.
Since there are in total 12 constellations for the sun to make its journey, it means sun stays in every constellation for about 2150 years on the day of the vernal equinox!