The start of September saw an unexpected announcement by NASA. With the help of amateur astronomers and the HST, a new feature was uncovered in Saturn’s far southern hemisphere that is gradually swinging into view. This decagon feature – a ten‑sided wave pattern encircling the planet’s south polar region, is analogous to the famous northern hexagon but far more subtle. In a validation of the merit of amateur observations, Trevor Barry’s meticulous IR imaging offered the kind of sustained, night‑to‑night coverage that professional telescopes can’t provide, giving scientists the confidence that the feature was genuine and not an artifact of limited sampling.
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| Location of Decagon Feature (credit: NASA) |
While Trevor’s equipment and expertise far outstrip my setup, I was still curious as to whether I may have inadvertently captured it during two imaging runs on nights of above average seeing.
My first attempt
actually came before the announcement. On August 26, with above‑average
seeing and Saturn riding high enough to justify a late session, I put the 742
nm IR‑pass filter on the QHY5III462 camera and captured a long sequence. At the
time, I was simply trying to record what the ringed planet was showing – maybe get
lucky and record a spoke (see last month’s blog entry) or even a low-contrast
white spot storm. In hindsight, that dataset became my “pre‑discovery” attempt.
After the story broke I was back out again on September 8, this
time using the Baader 685 nm R‑IR long‑pass, which has become the go‑to
wavelength for amateurs trying to tease out faint polar wave structures. The
seeing cooperated again, and I collected a solid run of data with the Cyrus 10-inch
f/6 Newtonian telescope using a 2.5x Barlow.
Both evenings provide some nice images. The decagon feature
lies at around -60°, so just north of the dark band that is part of the South
Pole complex. I started by inspecting that latitude for any sign of a
low-contrast belt, but I could not discern anything.
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| Saturn Sept 8, 2026 |
Doing a little research, plus seeing what some other skilled
amateurs were doing, I decided to run the images using the WinJUPOS polar
projection functionality. A polar projection gives you a better chance at
seeing the decagon because it removes the very geometry that hides it in a
normal “frontal” view. In a standard equatorial presentation, the south polar
region is heavily foreshortened, compressed into a narrow oval, and partially
affected by limb darkening. A stereographic south‑polar projection, on the
other hand, unwraps that entire region into a true top‑down map: the latitude
circles become concentric rings, the polar hood boundary becomes a clean
contour, and any geometric modulation (such as a ten‑sided wave) can emerge.
Alas, this also failed to expose the decagon’s existence.
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| Polar projection map and approximate location for decagon |
This subtle southern decagon may or may not be within reach of mid‑aperture telescopes. But the only way to find out is to keep pointing our instruments at Saturn and comparing notes. With my new experience of generating a polar projection map, even this “failure” comes with a silver lining of adding another skill to my processing resume. In the meantime I’ll be watching ALPO submissions closely as Saturn reaches opposition to see if other amateurs succeed and, if so, what equipment and techniques they employed.
