The Upanishads, Part 1 (SBE01), by Max Müller, , at sacred-texts.com
1. From the dark (the Brahman of the heart) I come to the nebulous (the world of Brahman), from the nebulous to the dark, shaking off all evil, as a horse shakes his hairs, and as the moon frees herself from the mouth of Râhu 2. Having shaken off the body, I obtain, self made and satisfied, the uncreated world of Brahman, yea, I obtain it.
143:1 This chapter is supposed to contain a hymn of triumph.
143:2 Râhu, in later times a monster, supposed to swallow the sun and moon at every solar or lunar eclipse. At first we only hear of the mouth or head of Râhu. In later times a body was assigned to him, but it had to be destroyed again by Vishnu, so that nothing remained of him but his head. Râhu seems derived from rah, to separate, to remove. From it raksh, to wish or strive to remove, to keep off, to protect, and in a different application rákshas, a tearing away, violence, rakshás, a robber, an evil spirit.