Positions of Comet Hyakutake and Ulysses on 1 May 1996
Relative positions of the Sun, comet Hyakutake, Ulysses and Earth on 1 May 1996. The orbital planes of the last three objects are labelled A, B and C, respectively.
Ulysses was near Hyakutake's orbital plane, at 3.73 AU from the Sun (1 AU = 149.6 million km), at a solar ecliptic latitude of ~45° north, moving southwards at 6 arcmin per day.
The comet had been at the same longitude as Ulysses' 1 May position around April 23.4 UT, and at Ulysses' 1 May latitude around April 24.0 UT [at heliocentric distances of around 0.35 AU (a)]. By 1 May, the comet was at perihelion, at 0.23 AU from the Sun (b).
The nucleus thus moved a considerable distance around its retrograde orbit (from a to b) while part of the tail travelled to Ulysses. The entire tail (shown in white) moved radially outwards which, combined with the comet's rapid motion, resulted in its strong curvature.
Assuming a rapid acceleration to the solar-wind velocity, it approximated an archimedean spiral in the comet's orbital plane, and measured >3.8 AU in length. Assuming the region encountered by Ulysses originated at (a) during 23 April, its radial path of 3.39 AU (dotted line) took 7.4 - 8.0 days to traverse.