Why are rainbows usually semicircles instead of complete circles?

[damitr]

All the rainbows that appear naturally, are usually semicircles, what is the reason for this, they could also be as little arcs as well. Are there any conditions under which a complete circle of the rainbow may be seen?

 

[michealsmith]

all r circular even the ones made naturally

 

[Renge Ishyo]

It could take that shape because the light is refracting from the insides of circular shaped raindrops? I know that the actual refraction through the raindrop is somewhat complicated (I think it is bent at 2 interfaces which seems to be why that upside down "2nd rainbow" with the reverse colors appears sometimes).

 

[jtbell]

Are there any conditions under which a complete circle of the rainbow may be seen?

Stand high enough above the ground so that the horizon doesn't block the lower part of the rainbow. Or if the water drops are close enough to you.. try it with water from a garden hose that has a spray nozzle.

 

[Kazza_765]

I haven't observed it myself, but I've seen photos taken from airplanes flying into or out of rainclouds and they can see a circular rainbow.

 

[Integral]

The arc of the rainbow is 42deg, thus any time the sun is below 20deg from the horizon you should be able to see more then a semi circle of the rainbow. In the future observe closely any evening rainbows you may encounter. I have personally observed this phenomena. It is also possible if the sun is high enough above the horizon to have no rainbow. This would occur in the summer at higher latitudes.

http://en.wikipedia.org/wiki/Rainbow#Physics_of_rainbows" says it better.

 

[jtbell]

Normally, when you see a rainbow, you're seeing light that has been reflected from raindrops that are fairly distant, so they're practically all above the horizon from your point of view. If the light is reflecting off drops that are close enough that some of them are below the horizon, then you might see the rainbow extend below the horizon. Or if you're in a hilly or mountainous area, you can sometimes see a rainbow in front of the mountains or hills.

 

[Ouabache]

If the water droplets are both above and below you, such as viewed from aeroplane (as Kazza 765 points out), you will see a circular rainbow.
Elaborating on Integral's comment on position of the rainbow: from any surface elevation, the primary rainbow appears 42 deg above the anti-solar point or ray. A secondary rainbow can appear 51 deg above the anti-solar ray. So if you look at the same rainbow from a higher perspective, you will see the primary rainbow 42 deg up, relative to your new position.

"Rainbows are not seen in midday since the whole 42° circle is below the horizon at most latitudes. So rainbows tend to be seen most in the later afternoon when a thundershower has passed and the sun from the west is illuminating the receding edge of an eastwardly moving raincloud." (same ref)

 

[Ba]

If you are in somewhere where there is a heavy mist and the sun is shining you will see the rainbow in a full circle. It starts at your feet and goes out from there in a circular shape. You're standing at the end of a rainbow, start digging.

 

[skywolf]

I was looking at a rainbow the other day and i noticed something that made sence
the sun is behind me
my shadow is in front
it looks like the center of the rainbow is where my eyes are on my shadow
i thought about that and it made sence
i was wondering if it was actually true