2025 January 20

Mars Opposition Blog 20 January 2025

Richard McKim

2025 January 20th

In the UK, the period around New Year and for nearly a fortnight afterwards was bitterly cold, with noon temperatures often staying a little below zero, and with thick frost upon lawns and foliage. Remaining for very long in the observatory always seemed to be an heroic performance. After a few cloudy days, the temperature has become more bearable. Nonetheless, some fine work has been done. This post includes data submitted up to the day of opposition (January 16).

I am posting a number of results, this time concentrating more upon observations made in the UK and Europe, and have included several from different observers for January 9-10, enabling some comparison of processing methods.

There have continued to be a number of small dust events at the edge of the cap. For example, Robert Stuart has sent me an image for January 15 where a small notch in the cap is shown on the morning side when the Syrtis Major was at the meridian. Others have confirmed this.

In the last few days the Director was struck by the slight blue tint in the Syrtis Major, glimpsed with the marking at the CM on the 15th, but more strikingly visible at the evening terminator days earlier. This coloration is due to the scattering of blue light by the thin cloud which populates the martian equator at this season (though the equatorial cloud belt is not yet complete before around Ls = 45). This effect has been shown by some images, and it has also been noticed over parts of Mare Acidalium with the marking near the morning limb. Paul Abel also remarked upon this. High resolution images have shown a small white evening cloud in the mid-latitude of the Syrtis. The orographic clouds mentioned last time are very prominent. Visually the Director noticed that the dark spot Nodus Alcyonius is still rather small and difficult to see. Will it disappear entirely, as it has in the past? And will Nepenthes ever reappear?

Tom Wiliams has submitted a remarkable video from January 3 which appears to show the shadows of evening white clouds (over Sinus Meridiani) as they rotate and reach the terminator. We have caught the long shadow of the Arsia Mons banner cloud at the appropriate season in the past, but imaging the shadows of the more usual evening equatorial clouds is (I think) a first in groundbased astronomy.

T.Akutsu imaged the martian moons on the date of opposition.

I find that my btinternet address sometimes blocks large group mailings. If you have sent something and have not had a reaction from me, please check! And if you are a new observer posting at the BAA website, please contact me directly by email in order to join the Section.

Now a final word about filenames. Whatever filename you assign to your image, and whatever its orientation, it will normally be archived by me SOUTH UPPERMOST in the following style, ending with the observer’s initials, like: 2025-01-15-2300UT-RJM. I allow variants like m20250115_2300_rjm, and so on, provided that the observer is consistent. But variants like 150125-RJM or 15Jan2025_rjm are NOT permitted. Each observer is assigned their own folder of observations in my filing system, for each apparition, and I need their images to appear in chronological order whenever it is opened. You may wish to add subdivisions of a minute of time, or the initial of any filter used before the final initials. If you want to tell me the camera or telescope or observing location or observing conditions it must all be written upon the image, or sent in an email (once per apparition will do), but not added to the filename.