[INDOLOGY] Symbolic Forms of the Navagrahas

[jacob at fabularasa.dk]

Dear friends and colleagues,

I am trying to understand the origin of the symbolic forms (ākāra) 
associated with the navagrahas, but have not had any luck so far. The 
standard forms, as far as I have been able to determine them, are as 
follows:

Sun = circle (vṛtta)
Moon = crescent (ardhacandra)
Mars = triangle (trikoṇa)
Mercury = arrowhead (bāṇa)
Jupiter = rectangle (dīrghacaturaśra)
Venus = pentagon (pañcakoṇa)
Saturn = bow (dhanus)
Rāhu = winnowing basket (śūrpa)
Ketu = flag (dhvaja)

I would be grateful for any pointers to primary sources or articles 
discussing these forms.

Best regards,
Jacob