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Proceedings Paper

Could Jean-Dominique Cassini see the famous division in Saturn's rings?
Author(s): Julien Lozi; Jean-Michel Reess; Alain Semery; Emilie Lhomé; Sophie Jacquinod; Michel Combes; Pernelle Bernardi; Rémi Andretta; Maxime Motisi; Laurence Bobis; Emilie Kaftan
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Paper Abstract

Nowadays, astronomers want to observe gaps in exozodiacal disks to confirm the presence of exoplanets, or even make actual images of these companions. Four hundred and fifty years ago, Jean-Dominique Cassini did a similar study on a closer object: Saturn. After joining the newly created Observatoire de Paris in 1671, he discovered 4 of Saturn’s satellites (Iapetus, Rhea, Tethys and Dione), and also the gap in its rings. He made these discoveries observing through the best optics at the time, made in Italy by famous opticians like Giuseppe Campani or Eustachio Divini. But was he really able to observe this black line in Saturn’s rings? That is what a team of optical scientists from Observatoire de Paris - LESIA with the help of Onera and Institut d’Optique tried to find out, analyzing the lenses used by Cassini, and still preserved in the collection of the observatory. The main difficulty was that even if the lenses have diameters between 84 and 239 mm, the focal lengths are between 6 and 50 m, more than the focal lengths of the primary mirrors of future ELTs. The analysis shows that the lenses have an exceptionally good quality, with a wavefront error of approximately 50 nm rms and 200 nm peak-to-valley, leading to Strehl ratios higher than 0.8. Taking into account the chromaticity of the glass, the wavefront quality and atmospheric turbulence, reconstructions of his observations tend to show that he was actually able to see the division named after him.

Paper Details

Date Published: 26 September 2013
PDF: 11 pages
Proc. SPIE 8864, Techniques and Instrumentation for Detection of Exoplanets VI, 88641M (26 September 2013); doi: 10.1117/12.2023759
Show Author Affiliations
Julien Lozi, The Univ. of Arizona (United States)
Ctr. National d'Études Spatiales (France)
Onera (France)
Jean-Michel Reess, LESIA - Observatoire de Paris (France)
Alain Semery, LESIA - Observatoire de Paris (France)
Emilie Lhomé, LESIA - Observatoire de Paris (France)
Sophie Jacquinod, LESIA - Observatoire de Paris (France)
Michel Combes, LESIA - Observatoire de Paris (France)
Pernelle Bernardi, LESIA - Observatoire de Paris (France)
Rémi Andretta, LESIA - Observatoire de Paris (France)
Maxime Motisi, LESIA - Observatoire de Paris (France)
Laurence Bobis, Observatoire de Paris (France)
Emilie Kaftan, Observatoire de Paris (France)

Published in SPIE Proceedings Vol. 8864:
Techniques and Instrumentation for Detection of Exoplanets VI
Stuart Shaklan, Editor(s)

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