From David Harper
I was gratified to see that blue moons appear in your excellent column
(Feedback, 30 January).
You cite Keith Dawson’s “Tasty Bits from the Technology
Front” website as the source of your information. In fact, Keith got much of his
information from a website run by my wife and myself, which can be found at
www.obliquity.com/astro/bluemoon.html. We have a Blue Moon calculator to
enable anyone to explore this fascinating subject.
I should point out that the “19 years = 228 calendar months = 235 lunar
months = 236 full moons” argument actually underestimates the frequency of blue
moons, which is in fact 4.1 per cent.
Hinxton, Cambridgeshire
