Halley's Comet appears approximately every three-quarters of a century.
Periodical cicadas (commonly known as the seventeen-year locusts) return, well, after seventeen years.
A more recently discovered (by yours truly) cyclical event is QEA (for Queen's English Anxiety), which seems to occur at intervals of a half-dozen years.
The first recorded occurrence of QEA was in the year 2000, upon the publication by J. Harrington, S. Palethorpe, and C. Watson of "Does the Queen Speak the Queen's English" in Nature magazine (the article itself being a popularization of the trio's findings originally published in the Journal of the International Phonetic Association in an article entitled "Monophthongal vowel changes in received pronunciations: An acoustic analysis of the Queen's Christmas broadcasts." The following excerpt from the abstract of the Nature article explains what the trio did and what they discovered:
. . . we analyse[d] vowel sounds from the annual Christmas messages broadcast by HRH Queen Elizabeth II during the period between the 1950s and 1980s. Our analysis reveals that the Queen's pronunciation of some vowels has been influenced by the standard southern-British accent of the 1980s which is more typically associated with speakers who are younger and lower in the social hierarchy.
And that was the cue for the launching of QEA. Media from London to Los Angeles rose up to the full height of cutesy-sarkiness. A Guardian (UK) editorial:
The Queen's English is modulating.
“My husband and I have had, y'know, a bituva tricky year, one way and annuvva. I mean, what with Chiles getting in all that hot wa'er about GM food and that, and then the flippin' Guardian sticking it to us with its, su'ov, anti-discrimination, Act uv Se'ulment thing. Anyway, bottom line: have a wikkid Christmas - plenty of turkey on the old plates, a few jars with your mates, you know the drill. You should all be well sorted.”. . . we suspect calculation here as well as mere social change. All today's most popular figures . . . speak mockney. The Queen is simply trying to get in on the act. They are nothing if not adaptable, these royals. Ain't that the truth, yer madge?A story in the Los Angeles Times began: