In the Rig Veda, Aryaman is described as the protector of mares, and the Milky Way (aryamṇáḥ pánthāḥ) is said to be his path.
Aryaman is one of the early Vedic deities. Ayaman means a ‘devoted friend’ or ‘Gentleman.’ He is the third son of Aditi, the mother of the Adityas. In the RigVeda Aryaman is described as the protector of mares, and the Milky Way (aryamṇáḥ pánthāḥ) is said to be his path. Aryamans royal path is milky way.
Aryaman Pantha is an expression which occures in Brahmanas. According to Weber it's Milky Way but according to Hillebrandt is elliptical.
List of the Brahmana Texts which mentions Aryaman Pantha.
- Taitariya Brahmana i ,7,6,6
- Pancavimsa Brahmana XXV 12.3
- Shatapatha brahmana 18.104.22.168
Here is Shatapatha Brahmana 22.214.171.124 quote.
For to Bṛhaspati belongs that upper region, and there above lies that path of Aryaman (the sun).
In the footnote of 5.3.2 it's said as follows "Whence the back of that upper region is white, or bright."
Generally Milky Way is also very bright in the night sky.
But according to some Books this is referring to Milky Way ,and as the path of Aryaman.
so it's look's like from the above that the bright path of Aryaman is above Bṛhaspati's path which according to weber is Milky way. May be That's the reason.