major problem arises: the new star is described as being to the South-East of Tianguan, while the Crab Nebula is to the North-East. This problem has been known since the 1940s and has long been unsolved. In 1972 for example, Ho Peng Yoke and his colleagues suggested that the Crab Nebula was not the product of the explosion of 1054, but that the true remnant was to the South-East, as indicated in several Chinese sources. For this, they envisaged that the angular unit cun corresponds to a considerable angle of 1 or 2 degrees, meaning that the distance from the remnant to ζ Tauri was therefore considerable. Aside from the fact that this theory does not account for the large angular sizes of certain comets, expressed in zhang, it comes up against the fact that there it does not make sense to measure the gap between a guest star and a star located so far away from it, when there are closer asterisms that could be used. In their controversial article (see European sightings, below) Collins and his colleagues make another suggestion: on the morning of 4 July, the star ζ Tauri was not bright enough and too low on the horizon to be visible. If the guest star, which was located close to it, was visible, it is only because its brightness was comparable to Venus. However, there was another star, brighter and higher on the horizon, which was possibly visible, for reference: Beta Tauri (β Tauri). This star is located at around 8 degrees north-north-west of ζ Tauri. The Crab Nebula is south-south-east of β Tauri. Collins et al. suggest therefore that at the time of its discovery, the star was seen to the south-east of β Tauri, and that as the days passed and visibility improved, astronomers were able to see that it was in fact a lot closer to ζ Tauri, but that the direction "south-east" used for the first star was kept in error. The solution to this problem was suggested (without proof) by A. Breen and D. McCarthy in 1995 and proved very convincingly by D. A. Green et F. R. Stephenson (2003). The term "stand on guard" obviously signifies a proximity between the two stars, but also means a general orientation: a guest star "standing on guard" for a fixed star is systematically located below it. In order to support this theory, Green