Hello again brown556! A rainbow is curved because of the way beams of light come out of waterdrops ( this is what gives us rainbows). The light goes into a raindrop (or other type of water) and is bent ( it changes direction, this is called refraction) then when it is inside the raindrop it reflects (like a mirror) and then bends again ( or refracts) when it leaves. The angle it makes when it leaves is what makes the rainbow appear curved. The llight then spreads out into a continuous range of colours. The colours are just the colours that, put together, make up all light.
Rainbows are actually full circles, not curved. We see them as curves when we are on the ground because the other half of the circle is blocked by the Earth at the horizon. You can only see the full circle if you are looking at a rainbow from above, e.g. in a plane, like the example here: http://www.extrospection.com/archives/2003/10/circular_rainbow.html
They form circles (or curves) for the reasons that Julie has explained. Reflection and refraction of sunlight changes the angles the light is travelling at. If you want to try and understand refraction better take a glass of water and place a pencil in it so that part of the pencil sticks out the top. When you look at the pencil from different angles it will appear ‘broken’ at the place it crosses the water surface.
Rainbows then have lots of colours because the ‘white’ light we see from the sun is actually made of 7 colours: red, orange, yellow, green, blue, indigo, and violet. The refraction (or bending) of the white sunlight changes each colour by a different amount so that you can then see them separately. You can try this yourself by shining a torch through a prism – ask your teacher if he/she has one you can try… 🙂
I don’t need to explain it, when James and Julie are here already 🙂
But I just tell you some other amazing facts about rainbow, because everyone loves rainbow…
Did you know:
1. Sometimes, there are two rainbows on the same day. Lovely! Even 3rainbows, or four rainbows are also seen.
2. There are some “rainbow” which appear at night, but then its called “moonbows” because the moon light making a rainbow.
3. The most amazing fact is that rainbow is in fact made up of millions of colors (apart from 7 distinct colors), most of which cannot be seen by human eyes.
HAVE A RAINBOW DAY, BETTER THAN A GOOD DAY!