A blue moon is one where there are two full moons in a calendar month.
Its a concept created by mans (womans?) organisation and the development of the Calendar over hundreds of years, there were and still are different calendars according to different religions, but basically we all (all around the world) use the same calendar for the ordinary everyday-world and business in the majority of places. Our calendar has ‘developed’ by people and been handed over by law from various empires all the way from before the Roman Empire over thousands of years and its measured the length of the year in days by the movement of the Sun, and months measured by the division of the year. Eclipses (and later computers) have checked the information by observation calculation and checking those ‘predictions.’
A Blue Moon means for most people something that doesn’t happen very often, something that’s out of the ordinary; but in the Astronomy ordinary world it means that there are two full moons in one ‘calendar’ month.
In the old days a Blue Moon was very important eg. if you were paid by, or paying employees (agricultural workers?) at the full moon in the month, or lending or borrowing from one moon to the next, or collecting or paying rent! Nowadays its a kind of soulfull music kind of idea and doesnt have much significance.
More interestingly thinking of Calendars while one of the greatest adjustments was taking place decided on by really clever medieval mathmaticians in the Middle Ages (the late 1500’s) Wollaton Hall was being built – at the same time that the Council of Trent and the Pope at the time were taking and deciding these important Calendar decisions (1582) that have resulted in our modern Calendar today. They were deciding what Calendar tweeks were needed around the time Francis Willoughby had commissioned the Hall – it was built from 1580-1588, Francis Willoughby in 1580 inherited from his gfather/uncle who was a ‘Knight of the Body’ and executor to the will of Henry vii (the same Willoughby or another was executor to Henry viii!) it was a matter of the gravest concern at the time (1582) to reconcile the Calendar dates with the Sun, Moon and Stars and decide on a sensible calculation that would last for millenia. Countries and Christian religions were and sometimes still are, debating the accuracy and ‘facts’ while other religions have their own calculations and celebrations – none of which happily, use the Blue Moon concept! They decided on the Calendar we have today and gradually it was accepted across the Christian Countries and the world.
When the Spanish Armada turned up in 1588 they sailed in a formation of the Moon to try to say England was out of date and hadnt taken the,Roman Catholic Calendar updates and wasnt working to the same day-date as Catholic countries (‘old’ and ‘new’ style)
We can even check today in the Moon and Sun cycles (Star Party, which constellation is rising) against our Calendar, and with the cycle of eclipses if we are patient enough over 19 years and in the ‘right’ location and check to see if our agreed timing system indeed brings the cycle back round on the ‘predicted’ (calculated) day and an eclipse happens. Or just count fron one Full Moon to the next to find the next full moon!!
More interestingly for curious people is to consider if there may possibly be clues in the Hall architecture, to those important decisions in the 1580s – maybe its the Prospect room to allow observations of the night sky!
There was a working Sundial in the formal gardens of the Hall for years and years, its still there but perhaps Nottm Council would be kind enough to put the Sundial time marker back on the plinth- its important! Thanks.
Incredibly complicated Calendar history here…
Sorry the link is soooo complicated!! and the post a little ‘geeky’ but its fascinating!