"Moonbows"

[catfisher]

\"Moonbows\"

I've just sailed the ARC (not in a Catfisher, I hasten to add!) ~ did anyone else see "moonbows", ie rainbows by moonlight rather than sunlight? We saw three, and they were quite stunning.

None of us had seen one before, nor ever heard anyone talk about them. We can't believe that we were the only ones to be so privileged.

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[JonA]

Re: \"Moonbows\"

I saw one about 20 years ago when on watch in the Coastguaed lookout at Prawle Point. It was quite an eery experiance.
Jonathan

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[Robin]

Re: \"Moonbows\"

We have seen them too on passage from Dartmouth to Camaret, mid channel and yes they are stunning. On another night we had the phosphorescence at maximum and went through several huge shoals of fish (mackerel?) that stirred it up and lit the area for 100's of yards around. People who only sail in daylight miss a lot!

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[AndrewB]

Do you mean ...

... a rainbow as with the sun, or one circling the moon?

Rings around the moon are not uncommon but a full-blooded rainbow is an eerie and omnious portent.

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[Robin]

Re: Do you mean ...

Just like with the sun!

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[TLX]

Re: \"Moonbows\"

What determines how bright the phosphorescence levels are at any one time?

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[Robin]

Re: "Moonbows"

I have no idea, sometimes there is lots of it and very bright and yet at other times just one or two occasional sparkles. It is even seen in the loo as you pump it! Some nights are very dark and if there is a lot of phosphorescence it shows up more I guess, though I do remember some brilliant nights sailing straight down a moonbeam to Cherbourg for the duty frees with a trail of the sparkly stuff stretching behind. I understand it is a problem for submarines which can be seen from satellites if they stir it up too.

Another night we saw (well SWMBO did, I was asleep!) a huge basking shark off Ushant, it apparently kept pace with us for a while whilst it and us stirred up the sparklies. I took a lot of stick for not responding to her cries of 'shark! shark!' and going back to sleep, muttering about dolphins (it was about 4am and I had just gone to sleep having crossed the last of the lanes). She had the last word by turning off the radar 'plot' feature which leaves a trace on the screen and which I could see from my bunk by opening one eye - she knew that the echos showing had all passed clear of us but it sure woke me up fast when I couldn't see their trail! Later in Camaret everyone was talking 'did you see those basking sharks last night, as big as the boat they were' - All I got was see, see you told me I was imagining it!

Night sailing does have some compensations.





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[FlyingSpud]

Re: \"Moonbows\"

The other good thing about phosphorescence is that it makes having a Pee over the side late at night an experience not dissimilar to the millennium fireworks in Sydney.

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[Mr Cassandra]

Re: \"Moonbows\"

Hi.
People who sail in the night, "don`t know what they have just missed " !!
cheers bob t

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[TLX]

What causes phosphorescence?

Found this:

Microscopic single celled (unicellular) algae called Dinoflagellates cause phosphorescence. These are present throughout the ocean, and emit light when they are mechanically disturbed, for example by a boat paddle, the arm of a swimmer or wave action. This leads to a chemical reaction within the organism, resulting in light production.

Dinoflagellates breed all year round, however, there are a number of factors that promote growth and reproduction, these are: light, water quality, temperature, availability of nutrients, and depth or tidal exposure.

As dinoflagellates depend on photosynthesis to get their energy for growth, light is a major factor in their survival. The intensity of phosphorescence by photosynthetic dinoflagellates is strongly influenced by the intensity of sunlight the previous day, ie. the brighter the sunlight, the brighter the flash.

If the preceding few days are sunny, and the ocean is calm so that the dinoflagellates are not disturbed, this can result in a build up of phosphorescent 'potential'. This build up when released can look like fireworks in the water.

The other thing that can contribute to such a display could be a concentration of nutrients in the water, most commonly caused by runoff from pollutants, such as sewage. This results in a build up of dinoflagellates.


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[TheBoatman]

Re: \"Moonbows\"

Pat
A man after my own heart<s>

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[bluejuice]

Re: \"Moonbows\"

saw two moonbows on the way up the carribean chain both just after squalls glad they are 'real' as becoming bit worryed as was the only person on deck at the time!!!

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