The sun has been referred to as Aja, perhaps because it is anādinidhana (anadinidhana) or the one without a beginning or an end—

gabhastimān ajaḥ kālaḥ.

Mahābhārata (Kinjawadekar)(3.3.16)
Mahābhārata Vols. 1-43 (Siddhāntabāgīśa)(3.3.16)