Abstract
We summarize the results of our Gegenschein observations at Norikura (altitude 2876 m, Japan) in Sept. 18, 1996, and at Kiso (altitude 1130 m, Japan) in Feb. 9-14, and March 4 and 5, 1997. The instrument consisting of fish-eye lens or the wide angle lens attached to the cooled CCD camera was used with green filter. It is found that the position of the maximum brightness near the antisolar point (the Gegenschein) is slightly deviated approximately 0.°4 from the antisolar point to the south in September, whereas nearly 0.°7 to the north in February/March. Furthermore, a gradient of the relative intensity along a line perpendicular to the ecliptic is remarkably different with changing seasons, i.e. the brightness decreases faster towards the north in September, in contrast with its quick decrease towards the south in February/March. Our observed evidence suggests that these variations of the peak position and the brightness gradient of the Gegenschein are caused by the annual motion of the Earth with respect to the plane of the zodiacal cloud, and does not conflict with the predictions deduced from the cloud model having its symmetric plane beyond the Earth's orbit coinciding with the invariable plane of the solar system.
