Saturday, 19 September 2009

A simple guide to Harvest Moon (not the game)

Next full moon is the Harvest Moon.

This means it is the nearest full moon to the autumnal equinox, where day and night are nearly equal length (click here to read about the vernal equinox all those summer days ago). The Harvest Moon often falls in September, with the equinox, so an October full Harvest Moon is quite rare; you could say this occurrence is more rare than a blue moon. 

People know the Harvest Moon - it's the the first Native American full-moon name people cite when I mention I'm moonwalking. There are some common misconceptions. Here they are--

1. It falls in September

No, not always. Two years out of three, the Harvest Moon will indeed fall in the same month as autumnal equinox. But sometimes we'll see an October Harvest Moon, like in 2009 when the October full moon falls on Sunday 4th.

2. It's brighter than other full moons

It's true that the Harvest Moon was more useful to farmers than other full moons; but it's nothing to do with its brightness (or 'albedo' (reflectivity), to avoid upsetting scientists). Night after night, the moon goes through changing faces, its phases. During this monthly cycle, she rises a little later every night - usually by about 50 minutes. However, over the time of Harvest Moon the moonrise time from one night to the next is closer. It's nearer 25-30 minutes. So the time between sunset and moonrise - which is pretty instant around full moon day - remains quite close. Thus more light for ye olde farmers to harvest ye olde crops.

3. Harvest Moon is so much bigger

It's an illusion. Although scientists aren't sure why, they - in fact we - know that the moon is not necessarily any closer in its apogee-perigee cycle around the equinox. Because we tend to see it closer to the horizon for a longer period at this time of the year, that may skew our judgement. This is one of several explanations. Take a look at this:

One look bigger than the other? Look again. Yes? I wonder why.

In the words of my old friend Sir Patrick Moore (who I met once), we just don't know.

4. It glows red

I was lucky enough to see my first moonrise looking out to sea from South Wales in June this year. I watched an enormous, fiery full moon rising swiftly from the water.

Of course, I didn't really see that. The moon is a dull rock reflecting sunlight. And we only see that 'moonlight' once it's passed through our atmosphere. And that's exactly where the red tint comes from. As we saw in the last point, the horizon trick could be a reason for why the Harvest Moon looks bigger than others. The horizon - and level of atmosphere light passes through near the horizon - is definitely the reason for the fireball. Low moon means light passing through a denser atmosphere and producing a red face.

Moor red moon stuff here

5. Harvest Moon (the game) is rubbish

Actually, it's not that bad. Yes, it's for five year olds but it's strangely addictive. I'm not sure I'd use it as a guide for biodynamic agriculture, but when you catch one of those big ol' fish it ain't half satisfying!

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