There is an invisible Sun and it’s inside you, in your heart. The Sun outside is a kind of metaphor for that, like how the ringing of an alarm clock becomes the sirens of a firetruck in a dream. Something exists in Reality and the dreamer interprets according to what happens to be around. The waking state is not different from the dream state. It works the same way, just add matter.
Your soul is a super-conscious Sun, with all that power. So why not tap into the external Sun if you are convinced it exists outside of you? Gayatri mantra is a mantra for Sun power, Life power, and total illumination:
Oṃ bhūr bhuvaḥ svaḥ / tát savitúr váreṇyaṃ / bhárgo devásya dhīmahi / dhíyo yó naḥ pracodáyāt