If I might respond...
>And when did it become customary to mark such periods anyway?
Probably when it no longer one month for people to get the news of the event.
>Did anyone think the passing of exactly one month after the assasination of the Archduke Franz Ferdinand in Sarajevo, Hitler's invasion of Poland, the dropping of the atom bomb, or the first human landing on the moon worthy of public notice?
In the case of the first three events it is a combination of my first point and the fact that there were other events happening of greater import.
>Is this just an example of the media being desperate for anything to fill those 24 hours of news programmes? [/old fogey rant]
To some degree it is unavoidable. It is however, more likely due to fact that it was such a monstrous event and it gives a chance to honour those souls who perished.
For the menstrual-versary (or mensual-versary) how about adapting the word "month's mind" defined in the OED as:
1. Eccl. In England before the Reformation, and still in Ireland among Roman Catholics: The commemoration of a deceased person by the celebration of masses, etc., on a day one month from the date of his death.
There seems to be no authority for applying the term to the commemoration throughout the month following the funeral. The notion that it meant a commemoration recurring every month is baseless. For an English rustic survival of the ‘month's mind’ custom, see month's end in month n. 6b.
1466 in Somerset Medieval Wills (1901) 210, I will that there be at my dirige mass and moneth mynde noon other tapers ne candelstikkes but such as be of the same chirch. 1487 in Paston Lett. III. 463 Every weke folowing unto my monthes mynde oon trentall, and iij. trentalles at my monthes mynde biside the solempne dirige and masse that is to be requyred for me at that tyme. 1530 in N. & Q. (1900) 9th Ser. VI. 414/1, I will that my executors cause an hole trigintall of masses to be saide+upon the day of my buryall+and likewise as manny at the moneths mynde and asmany at my yeres day. 1546 Langley Pol. Verg. De Invent. vi. viii. 128 In England the custome is to kepe the thirty daie or moneth mynde with like Obites, as wer dooen on the buriall daies. [Orig. Apud Anglos hoc fit vigesimo nono die postquam mortuus est sepultus.] 1565 Cooper Thesaurus, Cenotaphium, a monument of one dead where the body is not, as the herse at the monthes minde.
<RED>1721 Strype Eccl. Mem. II. iv. 281 The month's mind for the two Dukes of Suffolk late deceased was kept September 22: so the more solemn celebration of the funerals of great persons about a month more or less after their interments used to be callid. </RED>
1830 W. Carleton Traits Irish Peas. (1843) I. 163 He hadn't even a Month's mind! Ibid. note, A Month's Mind is the repetition of one or more masses, at the expiration of a month after death, for the repose of the departed soul. 1884 Weekly Reg. 11 Oct. 452/2 The month's mind of the late Marchioness of Londonderry was celebrated in the Catholic Church of Newtownards.
