BLIMEY, we're back on the old 'blue moon' topic again!

It's really amazing how even the most obscure of subjects manage to capture the eager interest of followers of this page. For all sorts of weird and wonderful theories flooded in after I'd asked how the expression 'once in a blue moon' came about.

Eric Dever, from Morecambe, wrote in claiming the saying erupted after the volcano Krakatoa shot fine ash into the air, in 1883, drawing a "blue veil" across the moon.

But regular correspondent Kevin Heneghan of North Road, St Helens, says that the theory, though ingenious, does not suffice.

"To say that the moon is blue -- that is, to believe in the absurd -- was first recorded in an old proverb in 1528". The rhyming proverb, in the written language of the time, went: 'Yf they saye the mone is beleue; We must believe that it is true'.

Kevin, who devotes countless hours researching historical fact and fiction, adds: "In those days, the expression meant never, as it was ridiculous to think of the moon as blue. But by the 19th-century it had come to mean very seldom.

"The change was possibly influenced by the fact that the moon does seem to have a blue tinge on rare, unusually clear nights".

This must have been noticed in earlier times but it was not recorded until 1860.

And that was 23 years before Krakatoa erupted.