Archeologists have found writing relating to astronomical cycles on the walls of a Mayan house.  There are two sets of glyphs, one describing lunar cycles.

The second set of glyphs is more obscure. Saturno thinks it relates to two Mayan calendars: a ritual calendar lasting 260 days and the solar calendar, lasting 365 days. The two calendars only show the same date once every 18,980 days – the so-called Calendar Round.

All the numbers in the second set are multiples of 18,980, suggesting they are anniversaries. They are also multiples of other astronomical cycles. But Saturno doesn’t know what they represent.

So, what do you think they represent?  What event that happens every 52 years could they have been recording?