2025 September 1

Mars Opposition Blog 1 September 2025

Richard McKim

2025 September 1

The closing chapter in the 2024-25 apparition has been the anticipated appearance of the northern cyclonic clouds at two longitudes: Mare Boreum and Utopia. The clouds were recorded by Foster and Lonsdale. In this image of August 6 (CM = 102, Ls = 121) by Foster, we first clearly see a bright morning cloud at the edge of the polar cap. The cloud is strongest in blue light and looks circular. Lack of resolution precludes having any idea of its internal structure, but its first appearance at the correct place and at the correct seasonal date guarantees its nature. There is also an interesting image by Ito on July 26 at nearly the same CM longitude (CM = 108) which hints at the same phenomenon in an enhanced colour image; however, the cloud is not so prominent, and there is no blue image available. Another such cloud seems to be visible at the morning terminator upon Foster’s August 12 image.

In this image by Lonsdale for August 6, we appear to see a N-S elongated cloud streak at Utopia, this time in the early afternoon, and it is likely (but not certain at this level of resolution) that this was another cyclonic cloud. Another Lonsdale image for August 3, not posted here, might also show another, smaller and brighter cloud.

The recent images from the above observers this month, taken together with others by Akustu, Hillebrecht, Ito and Melillo demonstrate the continuation of the seasonal equatorial cloud band (ECB) and the frost covering at Hellas. (But the observations will surely not continue long enough to time the cessation of these phenomena.)

In this image by Lonsdale on August 11, a thin strip of ECB crosses the southern Syrtis Major. From memory I can confirm that seasonally similar records were obtained by BAA members in 1901, 1903 (Denning) and 1967 (Botham), and doubtless in other years too. The cases cited were more striking as in these earlier instances the observations were made much closer to opposition.

Finally, Martin Lewis has finished his impressive personal 2024-25 apparition maps, and I post them here (and will later put them up on the front page). One version is lettered, and the other is not.

At the time of writing (August 25), the last image of the 2024-25 apparition had been taken on Aug 22 by Melillo, and the final drawing by Adachi on July 19. As the observing season is either over or very nearly so, this will almost certainly be my final BAA Mars blog post for 2024-25. In due course I will write up the observations for the 2022 and 2024 oppositions for the Journal. For now I repeat my sincere thanks to all who made contributions.