Subhash Kak in his Astronomical Code of the Rgveda dates the Rigveda to "4000-2000 BCE"; Kak's results have been criticized by Plofker as having "no statistical significance whatsoever", even if overlooking their being based on the structure of the Iron Age shakha (recension) of Shakala rather than the content of the actual Rigvedic texts.
"The One" referred to in the Nasadiya Sukta and other hymns has been suggested to have originally referred to the axis mundi, and "The One who dwells beyond the seven sages" as the polar star, at the time referring to Thuban (α Draconis).
The samvatsara "full year" in the Yajurveda has 360 days, and 12 (TS) or 13 (VS) months.
The visuvant (summer solstice) period is 21 days in Aitreya Br. and 7 days in Pancavimsa Br., the summer solstice being in the middle of the period.
The gavam ayana ritual in SB 4.6.2. is based on the motion of the sun.
In the Maitrayana Brahmana Upanishad (6.14), the year is said to be into two portions, with the part from Magha to half of Śraviṣṭha associated with Agni, and the part from Sārpa to half of Śraviṣṭha associated with Varuna and Saumya (the moon). Aiyar has argued that Agni suggests the warm half and similarly Varuna the cool half of the year, suggesting the summer solstice at the beginning of Maghā and thus implying the vernal equinox in Kṛttikā. This, according to Kak, would correspond to 1660 BCE.
The Shatapatha Brahmana mentions that the Krttikas (the Pleiades) "do not swerve from the east". This would have been the case with precision at 2950 BCE and was true also about 2000 BCE, but was still true to within 8-13 degrees (viz., East by north) around 800 BC, the assumed date of the text's composition.
The positions of the solstices and equinoxes in the Vedanga Jyotisha, with the sun very close to the Krittika at the Vernal Equinox., would correspond to about 1370 BCE, although the text in its present form is from a later date.
The Vedanga Jyotisha, in common with Mesopotamian texts, asserts a 3:2 ratio between the durations of daylight on the longest and shortest days of the year. This corresponds to a latitude of about 35 degrees.. A latitude of 34 degrees would correspond to Northern India.
http://www.youtube.com/watch?v=tMGPwHcuPc8