Wednesday 16 June 2021

Jupiter seen with a Cooke in Australia in 1896



I am glad to be able to report that observing conditions generally have been very good with us since the beginning of last month, and that at least one other member besides myself has taken advantage of the good seeing to make drawings of Jupiter. I am unfortunately divorced from my observatory for some months, but have with me in the country an excellent 5-in. Cooke altazimuth as well as accurate time.

I have never hitherto prosecuted a careful and continuous study of the giant planet's surface, and confess to great surprise at the vast and rapid changes that become apparent. This especially struck me first in the case of the N. equatorial belt, the northern and equatorial components of which exhibited alternately dark masses and condensations, divided by white spots after intervals of only five Jovian rotations. On March 13 and 14 there were typical instances of this. On March 26, 20h 40m, G.M.T., a faint wisp across the equator, was conspicuous, and next night, March 28, 2h 20m G.M.T., was invisible, while the equatorial region near the c.m. showed considerable change. Definition excellent, 4 to 5 on both occasions, power 200. The N. temperate area, however, has puzzled me most, for the three belts often seen have varied much both in visibility and latitude, while with exquisite definition on April 1, at 0h 20m G.M.T., the following portion seemed overlaid with vapour of a sage green tint, and the belts (2) were only faintly visible in their preceding parts, The Red Spot has been well seen on several occasions of almond shape, the f. end slightly more pointed than the p. Its tint seemed uniform, and a very delicate brick red, like a faint stain. It is overlaid on the S. side by the S. temperate belt, which is closely double through nearly its whole extent, and f. from the centre of the Red Spot is much darkened and sinuous. The great spot's preceding end was estimated on c.m. at 1h 15m G.M.T., April 1, and the following end on c.m. at 21h 52m 36s G.M.T. of same date. In the transit of Satellite I. on February 22, observed at Waverley, near Sydney, with my equatorial, the shadow must have been occulted by the satellite, which is perhaps worthy of note.


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