> And are you aware of any classical reference that gives a particular point
> in the sky that's regarded as the commencement of Aswini?
There is no real physical star at the beginning of Aswini.
Instead, with Lahiri/Chitrapaksha ayanamsa, we get Spica star in the middle of Chitra nakshatra (i.e. at 180 deg).
In recent years, Sri Chandra Hari did some good work and he placed Lambda Scorpionis star at the beginning of Moola nakshatra and came up with his own ayanamsa ("Chandra Hari ayanamsa"). His logic is based on some tantric tradition and he refers to Mooladhara chakra.
Mooladhara chakra is the basis of one's existence. More than Sahasrara chakra (1st house - head), it is the Mooladhara chakra (7th house) that needs to be fixed as the basis. I am inclined to agree with him on that. But I don't agree with identifying Moola nakshatra as the Mooladhara chakra.
Sahasrara chakra of Kalapurusha (natural zodiac) is at 0Ar0 (or closeby). Mooladhara chakra of the Kalapurusha is at 0Li0. The upper chakras are on one side and the lower chakras are on the other side.
Thus, fixing the zodiac based on the 180 degree point as the Calendar committee did is quite logical.
May Jupiter's light shine on us,