न तत्र सूर्यो भाति न चन्द्रतारकं नेमा विद्युतो भान्ति कुतोऽयमग्निः । तमेव भान्तमनुभाति सर्वं तस्य भासा सर्वमिदं विभाति ॥ १५॥ इति काठकोपनिषदि द्वितीयाध्याये द्वितीया वल्ली ॥

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English Translation

The sun does not shine there, nor the moon and the stars, nor these lightnings-not to speak of this fire. He shining, everything shines after Him. By His light all this is lighted.

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English Commentary

Sri Shankara’s Commentary (Bhashya) translated by S. Sitarama Sastri

The reply here is that it shines and is perceived as shining. The sun, though the enlightener of all, does not shine in the Brahman, being his âtman, i.e., the sun does not illumine the Brahman. Similarly, the moon and the stars do not; nor do these lightnings illumine. How could this fire, perceivable by us? Why say much? All these, the sun and the rest who shine, shine only after him, the lord of all; as water, firebrand, etc., from their contact with fire, burn after the burning fire and not by their own inherent virtue. It is by his light only, that all this, the sun and the rest shine. This being so, that Brahman alone shines and shines variously. From the various kinds of light possessed by its effects, the self-luminosity of the Brahman is inferred. It is not possible for one to impart to another luminosity, which one does not possess, because pots, etc., are found incapable of illumining other objects and the sun and the rest, luminous in their nature, are found capable of that.

S.Sitarama Sastri