Also known as circle of Ulloa, Ulloa ring, Ulloa’s ring, Ulloa’s halo, Bouguer’s halo, white rainbow, and fogbow. The eponym Ulloa circle refers to the Spanish naval officer, explorer, and astronomer Antonio de Ulloa y de Torre-Giral (1716–1795). It is used in meteorology to denote a rare *physical illusion consisting of a white luminous ring or arch that can sometimes be seen in mountainous regions, typically in foggy weather, while facing an area opposite the Sun (i.e. the antisolar point). Inside the Ulloa ring smaller rings or arches can sometimes be seen. These are known as glories or *Ulloa’s bows. Ulloa is commonly credited with having been the first to record both phenomena, after having observed them during an expedition in what is now Ecuador, between 1735 and 1739. As recounted by the French astronomer and author Nicolas Camille Flammarion (1842–1925), “Ulloa, being in company with six fellow-travellers upon the Pambamarca at daybreak one morning, observed that the summit of the mountain was entirely covered with thick clouds, and that the Sun, when it rose, dissipated them, leaving only in their stead light vapours, which [were] almost impossible to distinguish.