Longitude motion of knot N1, including all our data and those obtained from the analysis of the photographic images of 1952, 1971, and 1977 (empty circles with errorbars). The dot line is the linear fit obtained using the CCD images from 1999 and 2010 as in Fig. 7. The long-dash (blue) line is the fit for an eccentric orbit of period 86 yr, eccentricity 0.1, and passage at periastron in 1977.