दिवि सूर्यसहस्रस्य भवेद्युगपदुत्थिता।यदि भाः सदृशी सा स्याद्भासस्तस्य महात्मनः॥
divi sūrya-sahasrasya bhaved yugapad utthitāyadi bhāḥ sadṛśī sā syād bhāsas tasya mahātmanaḥ
Word by word
The verse says
If the light of a thousand suns were to rise in the sky at once, that might be something like the brightness of this great being.
In plain words
Sañjaya gives up on description and reaches for a comparison.
And notice how careful he is: yadi — if. Sadṛśī — something like.
He is not saying it was as bright as a thousand suns. He is saying that if you imagined that, you would be in roughly the right area.
Where you've felt this · in health
You step out of a cinema in the afternoon and the ordinary street is unbearable for about ten seconds. Nothing out there is unusually bright. The light is the same light that was there when you went in, and your eyes had simply stopped expecting it.
Going deeper
A comparison that admits it is only approximate is more trustworthy than one that does not, and the hedging in this line is deliberate.
Sañjaya could have said it was as bright as a thousand suns. Instead he builds a conditional: if such a thing happened, it might be something like. He is marking the edge of what language can do while still doing the best it can within it.
That is the same honesty that runs through the chapter's whole narrative frame.
And the image itself is doing more than indicating scale. A thousand suns is not just brighter than one sun. It is a quantity of light at which seeing stops working altogether — which is exactly the situation Arjuna is in, and the reason he was given a different eye before any of it began.