| The colors of Saturn in 2023 (1) Photometry and images by Christophe.P |
It's been two years now that I am able to make a photometric study of Jupiter, and here you will find my first one on Saturn :) The data has been obtained on two nights from last september although I have also partially used the data gathered in August at the AstroQueyras Observatory. In comparison with Jupiter, the difficulty of Saturn comes from the rings that almost always partially mask the globe. I have dedicated much time to read some scientific litterature in the hope of finding equations to deal with this problem but I didn't find how to do this. However, since I am working on disk resolved images, it is then possible to isolate the globe from the adjacent rings, letting only the part that passes in front of the disk. This is not a problem for the photometric calibration, in that case the frontal rings are just considered as a particular "banding domain". However, it make comparison with historical references less accurate. The values found are none the less right on track of the expected values from U to V. They are lower in R and IR, but this would easily comes from the fact that Saturn is approaching equinox, and the globe is getting less red, and less bright, during the process - values in R and IR are getting closer to the Karkoschka's spectrum that has been made in 1995 right when Saturn was at equinox. The albedo of 12% in CH4 is obviously affected by the bright rings. I am adding comparisons of images from 2022 but I did not make a photometric calibration back then. As for Mars, the calibration of the B425 filter is obtained through homemade magnitudes calculated from spectroscopy and looks also correct. In the second message (probably next week-end) I will send photometric profiles from north to south, to evaluate some of the color changes from 2022 to 2023, and in a third one we will talk about the rings themselves.
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