Of late I have been wondering about the possibility of an atmosperic optical phenomenon that must be truly tantalizing if it exists, namely the occurrence of two rainbows opposite each other, one caused by the sun, and the other by the full moon, when both are just above the horizon. I have never heard about such a phenomenon, but I cannot think of any reasons why it should be impossible, apart from the required circumstances being very rare. Of course it may be that the brightness of the sun causes any moonbow to be invisible, but does this mean there is no way of seeing it whatsoever?
I am eager to hear your thoughts and ideas about this.
Best,
Dirk
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Now that IS an intriguing puzzle ! Apart from the problem of light intensity from sun & moon, there are the problems of light paths and of terrain. The lower the light source towards the horizon, the higher the arc of the resulting bow appears. An absolutely flat terrain would get rid of the problem of hills or mountains blocking the light paths or the view of the observer. BUT the terrain is never completely horizontally flat because the Earth's surface is curved anyway. So, the optimum scenario would presumably be in the middle of an ocean. And, of course, there would have to be precipitation/airborne waterdroplets to create the refraction, but falling from clouds which did not obscure the view! I suppose that, in theory, technically it might JUST be possible BUT I'd think that the stronger sunlight would prevail unless airborne pollution near the horizon reduced it to an equal intensity of the moonlight !!! All the factors being right at the same short time-frame would be incredibly rare, if at all possible. GWW is going to reserve judgement, as her brain has reached overload. What do all the Physics Professors out there think? GWW
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Yes, I think the difference in brightness between sun and moon is the main problem. True, at low altitudes the sun is a lot less bright than normally, but the same goes for the moon, so their relative brightness stays heavily unequal. Still, as you say, if something caused the sun to be 'filtered' in some way, there might be a chance.
I think the best chance of seeing two rainbows at once is on a planet that has a twin sun...
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Also, wouldn't you have to be inside the rain shower to look both ways at the rainbow one way and the moonbow the other? Yet isn't it true that the best position to see a rainbow is with the sun behind you and the rain in front while you're under clear sky? In which case, to see a moonbow when turning to look the other way from a rainbow there should be more rain behind you in which the moonbow would form. Meanwhile, the rain falling the opposite side of you would filter the light, especially from the already weaker light of the moon...
In other words the positioning for either bow would be:
sun/you/rain/rainbow
or
moon/you/rain/moonbow
But for both it should have to be
sun/moonbow/rain/you/rain/rainbow/moon
making it more unlikely coupled with the light intensity problem.
Or am I wrong?!
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No, you're absolutely right; I have been thinking the same. But what if there somehow was a 'hole' in both rain showers through which the sun and the moon could shine, while still leaving enough rain around them for the bows to form. There doesn't have to be rain at the center of the bows, only at the edges. But, again, I totally agree on the immense rarity of such circumstances.
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Wonderful picture Andrew. Can you, or any of our other experts, explain why the sky outside the rainbow is so much darker than that within? And what time of day do you think it may have been taken?
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Well, not being an expert and not sure I follow it myself, nevertheless, my explanation for the darker area outside of the rainbow is this:
All the light is being reflected at differing angles from inside the water drops - those different angles help make up the rainbow. But above the rainbow, the angles miss our eyes (or the eyes of the observer) leading to a darker area. Plus, inside the rainbow, a certain amount of light is also reflected straight back at the observer from the outside of the rain drops making a slightly lighter area inside.
That's my understanding, expressed in plainer English, of the mathematically explanation! Somebody, please correct and improve!
As to time of day - well it's obviously sunrise or sunset. I associate sunrise with a whiter light (like in that photo) and sunset with a yellower (all the dust of a day's action?) So I'd say sunrise. But, maybe that mountain area has cleaner air, so sunrise and sunset are more similar in tone? Anyway, am I wrong about a yellower sunset generally?
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August's cloud of the month last year has an explanation of 'Alexander's Dark Band', the darker area outside a rainbow. You may find it helpful.
Wendy
PS. I hope you managed to get some rain in your corner of Australia. We've had some here in Brisbane, but not enough to lift 'Level 5' water restrictions - the dams needed to be 40% full, and we 'missed it by that much!'. Maybe another day.
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Thank you Andrew for putting your explanation in plain English, and Wendy for directing me to the August Cloud of the Month's version. Fascinating... Ian, did you write that?
Although I leave for work in the dark and return in the dark (in this season) I have never seen a rainbow at any time other than full-daylight. The nearest I got was one evening when I saw a fragment of one near sunset. Will try to post the photo.
Yes Wendy, we have had substantial rains which have brought relief to gardeners, some farmers, and lifted all our spirits. However, nowhere near enough to alleviate the problems of our major river systems. The State Government is thinking of "letting the Coorong die". Sorry to become tangential for non-Australian members, but this is a disaster for our country.
And, speaking of disasters, I hope Andrew (Kirk) that you are nowhere near the extensive bushfires (I think you call them "wildfires") in California, and that Andrew (Poth) hasn't been troubled by the recent earthquakes.
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...thanks for asking. The earthquake was a long way from us. It just felt a minor tremor by the time the waves reached Tokyo. Lucky it was such a rural area - the damage/changes to the landscape were pretty major in a small area. Impressive.
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Andrew (Kirk) thanks for the photo. In relation to Andrew (Poth's) suggestion, I'm seeing both sunrises and sunsets frequently at this time of year in South Australia. I think you're right Poth, in that the yellow is the result of light through pollution in the air, but whether or not this occurs at sunset or sunrise seems to be due to where one is in relation to the pollution. Andrew Kirk's sunrise seems to support that.
When I see the sun rise I am looking toward the clear air of the hills and countryside, whereas when I see it set I am looking through the city smog, so I had always thought sunsets to be yellow. I will have to wait till I am west side of a polluted area to test this. A bit difficult where I live... would have to catch a boat as the city lies between where I live and the sea. But (and I hope I am not maligning Tokyo) I guess you would see sunrise and sunset through similar air Poth?
BTW glad to hear both our Andrews are safe from disasters!
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