Di, between Lupus and Centaurus. It shone so brightly that objects on the ground could be seen at night. By December, it was again sighted in the constellation Di. The Chinese astrologer Zhou Keming, who was on his return to Kaifeng from his duty in Guangdong, interpreted the star to the emperor on May 30 as an auspicious star, yellow in color and brilliant in its brightness, that would bring great prosperity to the state over which it appeared. The reported color yellow should be taken with some suspicion however, because Zhou may have chosen a favorable color for political reasons. There appear to have been two distinct phases in the early evolution of this supernova. There was first a three-month period at which it was at its brightest; after this period it diminished, then returned for a period of about eighteen months. A petroglyph by the Hohokam in White Tank Mountain Regional Park, Arizona, has been interpreted as the first known North American representation of the supernova, though other researchers remain skeptical. Earlier observations discovered from Yemen may have seen SN 1006 on April 17, two weeks before its previously assumed earliest observation. Remnant SN 1006's associated supernova remnant from this event was not identified until 1965, when Doug Milne and Frank Gardner used the Parkes radio telescope to demonstrate a connection to known radio source PKS 1459−41. This is located near the star Beta Lupi, displaying a 30 arcmin circular shell. X-ray and optical emission from this remnant have also been detected, and during 2010 the H.E.S.S. gamma-ray observatory announced the detection of very-high-energy gamma-ray emission from the remnant. No associated neutron star or black hole has been found, which is the situation expected for the remnant of a Type Ia supernova (a class of explosion believed to completely disrupt its progenitor star). A survey in 2012 to find any surviving companions of the SN 1006 progenitor found no subgiant or giant companion stars, indicating that SN 1006 most likely had double degenerate progenitors; that is, the merging of two white dwarf stars. Remnant SNR G327.6+14.6 has an estimated distance of 2.2 kpc from Earth, making the true linear diameter approximately 20 parsecs. Effect on Earth Research has suggested that type Ia supernovae can irradiate the Earth with significant amounts of gamma-ray flux, compared with the typical flux from the Sun, up to distances on the order of