This is what Professor Hans Henrich Hock wrote (original paper written in 2000 CE) and published as a chapter in a book “Indo-Aryan Controversy: Evidence and Inference in Indian History’ (2005).
“Was intercalation used on a yearly basis? That is, were the months entirely
lunar (consisting of 27 or 28 days), and the thirteenth month was inserted
every year? If so, at what point in the cycle was it inserted? If this was not
the case – as suggested by the fact that  mentions six sixtwelve
months for the course of the sun – at what yearly intervals were intercalary
months inserted, and what, therefore, was the number of days per month (the
Vedic texts range between 27 and 35 days)? Given a rough correlation of
1 day1 or 72 years of precession, the difference between 27 and 35 days,
that is 8 days, would translate into a variation in time depth of 576 years.”
Vedic texts do provide (various passages in various places.. not ONE SINGLE PLACE) varying days for the length of the month.
This is because Vedic calendar is one of the most precise and intricate calendar (if not the most precise) available in the world.
Our professor not only failed to recognize this intricate arrangement (of varying length…depending on which month it was referring to) of this wonderful Vedic calendar (there is no one single Vedic calendar.. rather Indian Luni-solar calendar is most appropriate term), he came up with a clumsy and most un-original way to claim this as an inaccurate calendar, riddled with error of 576 years! Well done Professor!
And AIT Nazis and AIT Sepoys are lapping up this nonsense since….
Professor is indeed right in stating the range of 27-35 days for the length of a month. Let’s understand why this is the case and where our esteemed professor went haywire.
(1) The moon takes 27.3 days to complete one full revolution around the earth with respect to the background stars (noted down in Indian tradition with the help of Nakshatra system). This is ‘the sidereal (lunar)month’.
(2) However, since the earth also moves through about those many degrees (~27-30) through its own orbit around the sun, during this time, the moon must travel slightly more than full circle (360 degrees) to get to from one new moon to the next (to be in the same phase (chandrakala) with respect to …as seen from the earth). This leads to a time interval of ~29.53 days. This is the synodic (lunar) month.
(3) For civic purposes, this fractional number 29.53 could be (and is done) rounded off to 30. This is the civic month (lunar) of 30 days.
(4) Indian literature describes year of 12 months and also of 13 months (intercalary-adhika masa).
(5) Length of Adhika masa (not always) is sometime described as of up to 35 days (This is what our professor refers to as length of month = 35 days, while conveniently (or ignorantly) ignoring the fact that this only applied to Adhika masa (and not always).
(6) Indian year is also described (in some places) as of 360 days with correction of up to additional 6 days. It is easy to understand (based on points 1 through 5 above) that a year of 360 days would refer to a civic year of 12 months with each month consisting of 30 days. A civic year will not able to keep up with changes in lunar phases over a long term, however can be employed simply as a count towards measurement of solar year.
What a marvelous creation! Only if one is capable of understanding the beauty of this precise calendar.
To be continued…