This article is about the calendrical, climactic and especially cosmological implications of Karthigai Deepam, an ancient Tamil celebration pivoted around the lighting of lamps that precedes Deepavali, the quintessential, ubiquitous but also comparatively recent festival of lights. Karthigai Deepam signals the end of the rains, intensifying winter chills and winds and shorter days. Juxtaposing festival observances in homes and those in temples, I demonstrate how its overriding concerns with generating light and warmth are part of ritual efforts to defend against elemental and existential threats of darkness and cold. Linking sacred time and mythical events with chronological time and human activities, this calendrical ritual joins together the divine and the mortal. Tracing the movement of fire and its various iterations as it traverses and connects the natural, cosmic, temple and home, this festival, I propose, renders the cosmic intimate and the intimate cosmic. Some rituals not only embody but also put cosmology into dynamic practice.