Bhashya
पर्जन्यो वा अग्निर्गौतम, द्वितीय आहुत्याधारः आहुत्यो-रावृत्तिक्रमेण ।पर्जन्यो नाम वृष्ट्युपकरणाभिमानी देवता-त्मा ।तस्य संवत्सर एव समित्; संवत्सरेण हि शरदादि-भिर्ग्रीष्मान्तैः स्वावयवैर्विपरिवर्तमानेन पर्जन्योऽग्निर्दीप्यते ।उत्तिष्ठति, यथा समिदाश्रयेण धूमः ।रात्रिः अर्चिः, समि-त्संबन्धप्रभवसामान्यात् ; अग्नेः समित्संबन्धेन हि अर्चिःसंभवति, तथा पृथिवीसमित्संबन्धेन शर्वरी ; पृथिवीछायां हिशार्वरं तम आचक्षते ।चन्द्रमा अङ्गाराः, तत्प्रभवत्वसामा-न्यात् ; अर्चिषो हि अङ्गाराः प्रभवन्ति, तथा रात्रौ चन्द्रमाः ;उपशान्तत्वसामान्याद्वा ।नक्षत्राणि विस्फुलिङ्गाः, विस्फु-लिङ्गवद्विक्षेपसामान्यात् ।तस्मिन्नेतस्मिन्नित्यादि पूर्ववत् ।वृष्टिं जुह्वति, तस्या आहुतेः अन्नं संभवति, वृष्टिप्रभवत्वस्यप्रसिद्धत्वात् व्रीहियवादेरन्नस्य ॥
In plain words
Parjanya is fire, Gautama -- the second fire in the pattern that keeps recurring through these offerings. Parjanya is simply the name for the power presiding over rain. The year is its fuel: as the seasons turn from autumn round to summer, that turning is what kindles this fire. [The clouds] rise as its smoke, exactly as ordinary smoke rises from ordinary fuel. Night is its flame, on the same principle that a flame comes from fire meeting fuel -- night-darkness comes from fire meeting the earth as its fuel, since what we call the darkness of night is really the earth's own shadow. The moon is its coals, because coals come from a flame the way the moon appears once night has fallen -- or simply because both have dimmed. The stars are its sparks, scattered across the sky the way sparks scatter. Into this fire the gods pour rain, and from that offering comes food -- everyone already knows that rice and barley and all food grow out of rain.
Close to the Sanskrit
Parjanya, indeed, is fire, O Gautama -- this is the second receptacle of oblation, in the recurring order of the oblations. Parjanya is the name of the deity who presides over the agency of rain. Of it, the year alone is the fuel; for by the year -- whose own parts, from autumn to summer, revolve in succession -- Parjanya the fire is kindled. [The clouds, as smoke,] rise up, just as smoke does through its connection with fuel. Night is the flame, because of the shared feature of arising through connection with fuel; for indeed flame arises from fire's connection with fuel, and likewise night-darkness arises from the earth's connection [with fire] as fuel; for they call the earth's shadow 'the darkness of night.' The moon is the coals, because of the shared feature of arising from that [flame]; for indeed coals arise from flame, and likewise the moon appears at night; or because of the shared feature of being dimmed. The stars are the sparks, because of the shared feature of scattering like sparks. 'In this, in this very [fire]' and so on is as explained before. They offer rain; from that oblation, food arises, because it is well known that food such as rice and barley arises from rain.