Observations of the Minor Planet 1566–Icarus

Abstract

AT the Cape the faint and fast moving asteroid, Icarus, was successfully registered on plates which were taken in each of eleven observable nights from June 18 to July 12. During this period its magnitude varied from 13.8 to 18.0, the latter being the limit for the Cape instruments. On each night simultaneous exposures were made on both the Victoria 24 inch blue refractor with IIa-O baked emulsion and on the adjacent 18 inch yellow refractor with 103a-D emulsion plus a yellow filter, in order to identify Icarus with certainty from spurious images. Schedules of observation for each night were prepared in advance for the shift of the telescope at regular intervals according to the predicted motion of Icarus. The intention was to keep its image stationary on the plates to within 3 to 4 s of arc. The 8 inch guider with a movable eyepiece was used to set on off-set guide stars, selected so as to have Icarus very close to the plate centres. Division heads were fitted to the screws attached to the eyepiece so that the latter could be set to within 0.01 mm (0.3″).