Now here’s a thing. Sometimes a puzzle idea comes as a result of another puzzle. You’ll be setting a puzzle and a little nugget chips off, and you look at it, and you realise there’s another puzzle there. So you finish the first puzzle and turn your attention to the offspring, and finish that as well.
And that’s where I am at present – only the offspring has appeared first, which rather limits my ability to talk fully about its origins. When the mother puzzle appears, all will be revealed. Don’t worry – I’ll link back to here when it does.
So, this may be slightly bland. The good bloggers and commenters at fifteensquared have already weighed in (with a splendid animation!). They’re quite right in noting my background in astronomy, though I can’t say it was working at full tilt when the idea struck. There was a newspaper article about the Moon Illusion and, as you do, I thought ‘Phenomenon –> Puzzle?’. The big issue was how to securely indicate the large moon, and the ‘one letter in four squares’ came promptly to mind. It provides a neat surprise when words don’t quite fit, forcing the solver to wonder why. It took a lot of fiddling to get the smaller MOON in place – I think this was because I was keen to ensure all the sixteen squares for the big moon were fully checked. Consequently there was a huge barless space in the NW of the grid as well, making it tricky to hook the little MOON in. Consequently, too, I cannot now look at the grid without thinking: “All that blank space – isn’t it obvious something is going on there?”
The puzzle has generated some debate at fifteensquared about the use of Google or Wikipedia. I find it surprising that there remains a group of people who insist that finding something in a reference book is OK, but finding the same datum online is somehow besmirched. I can’t see where the principle differs. Certainly from a practical point of view, if I need to verify something in a Listener puzzle, and I cannot do so from my shelf of reference books then I go online. If I have to wait to get into Wellington Library (which is a splendid example of the breed, even if they have just demolished its most striking architectural feature for fear of earthquakes) then I won’t be entering, because I need to get my entry posted first thing Monday morning to meet the deadline. From my point of view it’s e-entry or e-reference.