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How short is the shortest day?

Dec 21, 2016
4 min

How short is the shortest day?

Happy Yule! As you probably know, Yule (Jól) was the pagan Nordic celebration of the bleak midwinter. And it’s the winter solstice today – the shortest day of the year. What does that mean? The word solstice means “stopped Sun” in Latin – so it’s not really a whole day, but the moment when the Sun appears to stand still at its most southern point (so, furthest away from us in the northern hemisphere), before returning back towards the north. To put it another way, it’s the

The start of summer?

Jun 20, 2016
3 min

The start of summer?

Facebook greeted me today with this little graphic: Given that this is the radar picture over the UK this morning, it’s not surprising that several Facebook users felt a certain irony. But in what sense is it the first day of summer? As the Met Office explain in a lovely clear blog post, it depends whether you’re talking about the meteorological summer or the astronomical summer. For our forecasting friends, summer began three weeks ago on 1 June. (Though as my wife often

Drawing up a medieval horoscope

Jun 2, 2015
4 min

Drawing up a medieval horoscope

I’ve written a blog post entitled “How to cast a medieval horoscope” before. But I didn’t tell the whole story. Regular readers of this blog (are there any?) will know that the main focus of my research is equatoria – devices designed to compute the positions of the Sun, Moon and planets. I’ve made and used two of them – three if you count the fully functional virtual model which I helped create (though I can’t claim much of the credit – that goes to the amazing Ben Blundel

The Moon on a stick*

Dec 12, 2012
3 min

The Moon on a stick*

*well, on a disc of MDF, anyway. Want to know how to find the moon? Of course you do! So far on this blog I have constructed and calibrated a medieval planetary equatorium, and shown you how to use it to find the longitudes of the planets (most recently Mercury). Now it’s the turn of the Moon. This will be a two-part post, because – unlike for the planets – our equatorium will not only tell us the longitude of the Moon, but also its latitude. Celestial longitude is measured

Medieval Craftsmanship, Part 3

Nov 12, 2012
4 min

Medieval Craftsmanship, Part 3

[Drumroll] Ladies and gentlemen, I shall now demonstrate the use of a medieval planetary equatorium! In the first two posts in this series (here and here) I described how I made the physical structure of an equatorium according to the instructions in a fourteenth-century manuscript, and explained how I marked out the equatorium so that it could be used to find the location of the sun, the moon and the planets. (Technical point: skip this paragraph if you’re not interested.)