Was the northern hexagon of Saturn seen from Earth before Voyager 1? Further researches.

Abstract

Saturn's atmospheric boreal hexagon, discovered by the Voyager 1 probe in 1981, has such dimensions – sides km. 13800; total extension in length almost km. 30000; latitude 78°N; major angular diameter 4″; smaller angular diameter 1.3″ – to make it visible from Earth with common telescopes. Nowadays it is photographed with instruments with a diameter of 36 cm (Celestron C14) and digital image processing. We therefore wondered in the recent past if it had ever been reproduced in telescopic images prior to 1981. A systematic archive research conducted by us (Walter Ferreri, Mario Codebò, Barbara Bubbi 2021a; 2021b) in the two-year period 2020-2021 allowed us to find old drawings, performed starting from 1898 by the astronomers E.E. Barnard and E.M. Antoniadi with various refractors, in which the hexagon was reproduced although never mentioned in the writings. In the summer of 2022 Henry de Santis then found a drawing by the Italian astronomer Luigi Taffara from 1929 which presents the same reproduction of the hexagon. Two facts are noteworthy: 1) all the reproductions found so far have been copied from images obtained with refractor telescopes of various diameters, but never with reflectors; 2) the dates on the drawings show that the hexagon has persisted on Saturn's north pole since at least 1898. Further research in the archives of the Lowell Observatory, carried out by Laura Citernesi, demonstrated that professional photographs, taken in the first half of the 20th century, consistently did not have sufficient resolving power to show the hexagon. In this article we present and discuss all the images found to date.

Keywords

• saturn
• boreal hexagon
• voyager 1
• old astronomical drawings
• telescopic images
• archive research.