Comets and meteors have fascinated humans since they were first spotted in the night sky. But without science to aid understanding these spectacular apparitions, ancient cultures often turned to myth and legend, influenced by astrology, religious beliefs, superstitions, and human psychology. Cultural legends inspired a terrible dread of these celestial nomads, usually harbingers of death, destruction, and pestilence. Their sudden and unexpected arrival in the skies and sword-like appearance reinforced their beliefs. Were these divine messengers sent by the gods or gods themselves worthy of worship? Did they presage wars, famines, calamities, plagues, and death, or were they good omens that foretold the ascendance of a great leader? These characterizations are commonly known as apophenia, the perception of connections and meaningfulness in unrelated things that can be a normal phenomenon or an abnormal one, as in seeing ominous patterns where there are none. In Thailand, comets are known as dao hang, meaning tail star. Perceptions of comets in ancient Thai culture shared many Chinese and Indian aspects through trade, astrological, and religious (Buddhist, Hinduism) beliefs. During the period of trade and exchange, first by the Portuguese, then British, Western influences entered this region (e.g., the opening of Thailand to western culture by King Rama IV in the nineteenth century). It is certain that many indigenous beliefs predated those from outside influences, both from animism, spirituality, and superstition. A Thai scroll from the British Library called Tamra Phichai Songkhram (1800–1880), meaning “a divination manual for the prediction of wars and conflicts,” includes the interpretation of the appearances of comets and other celestial objects. Accurate illustrations of comets are shown with positional information. They portend calamities, assassinations, monetary rewards, and military operations, defeats, and victories. The scroll dates from 1800 to 1880, including the reigns of the Siam kings, Rama IV (the father of Thai science) and his son, Rama V, who witnessed several prominent comets, including the Great Comet of 1811 (C/1811 F1 Flaugergues) and Comet Donati (C/1858 L1). Rama IV gained astronomical knowledge using traditional Siam texts based on Indian sources and studied English texts as well. This paper attempts to elucidate these diverse influences on the cultural perceptions of comets in Thailand.