Why are rainbows curved?

[amarillis]

Why are rainbows shaped the way they are, and can you ever get upside down ones? (This isn't a homework question by the way, I'm just a little bored at work!)

[fo3nix]

Firstly, the earth is (near) spherical. So this is why it curves, and why it curves the way it does. It can't flip the other way round.

Also, light travels faster through different types of air (different air densities). This is why you get mirages in the desert, and on hot days tarmac looks like its wet from a certain distance. The same effect also explains the curvature of a rainbow. This curvature is due to the different densities of the material in the air that the light is travelling through, and the curvature of the air densities is largely contributed to by the shape of Earth.

[Loosehead]

The shape of the Earth is not relevant, it's to do with the shape of the raindrops, Ie spherical. Rainbows are round and when you are near the ground they are cut in half, you can see a curcular one from a plane. There can be upside down rainbows, I have seen a photo on the net I'll see if I can find it. Upside down rainbows are caused by a reflected sun say from a lake. Everyone sees a slightly different rainbow depending on positioning.

[Hammer]

Play around with a hosepipe on a sunny day with the sun behind you and you'll see a complete small round rainbow.

[Loosehead]

Upside down Rainbow here:

http://www.rense.com/general61/rainbow.htm

[Space]

fo3nix's answer is completely wrong. The shape of rainbows has absolutely nothing to do with the shape of the earth.
Rainbows are not created by different air densities at all, they are created by the rain drops refracting and reflecting the light that comes from the sun.

Rainbow actually have a circular shape, but you can't see the lower bit because the ground stops the rain drops from going below the horizon.
If you are on a plane, however, the ground doesnt stp you from seeing the full rainbow. ( look for "circular rainbow" on google images )

The reason why it's a circle is because there has to be a certain angle between the sun, the raindrops, and the viewer. All raindrops that match this angle form a circle, from the viewer's point of view

[Loosehead]

well coincided, Space!

[fo3nix]

you're quite right, not sure what I was thinking there. oops!

my excuse is that im currently in the middle of major exams. shame they're physics exams though; i really should be good at physics questions! oh well. at least the correct answer has been found :)

[MargeB]

how is the link able to open my history file?

[Davidgrey]

 

Just for interest sake, I'm a pilot and can tell you that even from 10,000 feet above ground level the rainbow looks exactly as it does from the ground except that we're looking down at it and you can see both ends of it. If there is a pot of gold at the end, I'm **** out of luck so far because there has never been a runway there to land on to get it........

[Dagman]

all rainbows are almost the same angle from the viewer wherever you are. Check out this page, for an explanation

http://farside.ph.utexas.edu/teaching/302l/lectures/node 113.html