SN 1006 was a supernova that is likely the brightest observed stellar event in recorded history, reaching an estimated −7.5 visual magnitude, and exceeding roughly sixteen times the brightness of Venus. Appearing between April 30 and May 1, 1006, in the constellation of Lupus, this "guest star" was described by observers across China, Japan, modern-day Iraq, Egypt, and Europe, and was possibly recorded in North American petroglyphs. Some reports state it was clearly visible in the daytime. Modern astronomers now consider its distance from Earth to be about 2,200 parsecs. Historic reports Egyptian astrologer and astronomer Ali ibn Ridwan, writing in a commentary on Ptolemy's Tetrabiblos, stated that the "spectacle was a large circular body, 2 to 3 times as large as Venus. The sky was shining because of its light. The intensity of its light was a little more than a quarter that of Moon light" (or perhaps "than the light of the Moon when one-quarter illuminated"). Like all other observers, Ali ibn Ridwan noted that the new star was low on the southern horizon. Some astrologers interpreted the event as a portent of plague and famine. The most northerly sighting is recorded in the annals of the Abbey of Saint Gall in Switzerland, at a latitude of 47.5° North. Monks at St. Gall provide independent data as to its magnitude and location in the sky, writing that "[i]n a wonderful manner this was sometimes contracted, sometimes diffused, and moreover sometimes extinguished ... It was seen likewise for three months in the inmost limits of the south, beyond all the constellations which are seen in the sky". This description is often taken as probable evidence that the supernova was of type Ia. In The Book of Healing, Iranian philosopher Avicenna reported observing this supernova from northeastern Iran. He reported it as a transient celestial object which was stationary and/or tail-less (a star among the stars), that it remained for close to 3 months getting fainter and fainter until it disappeared, that it threw out sparks, that is, it was scintillating and very bright, and that the color changed with time. Some sources state that the star was bright enough to cast shadows; it was certainly seen during daylight hours for some time. According to Songshi, the official history of the Song Dynasty (sections 56 and 461), the star seen on May 1, 1006, appeared to the south of constellation