rainbows??

hey, I have always wondered, why are rainbows always in an arch shape??? how is that shape always formed??

Relevance

Have you ever seen a "sundog"? It's kind of like a rainbow, except it's formed by ice crystals, not water droplets. Sundogs form when the sun's rays pass through the ice crystals and are refracted at certain angles. (Hang on, this is going somewhere...)

Depending on the shape of the ice crystal (cylinder, plate, flake etc...) that the light is passing through, the angle of the refraction will change. (If the angle of refraction is small - the arc will be near the sun, if the angle is big - arc will be a big circle around the sun.)

Now back to rainbows... Water refracts light in at much larger angle than ice (Biiig circle...). Also, you most often see a rainbow when the sun is shining through falling rain (duh.) - when it (the sun) is lower in the sky.

Both of these add up to a very big angle "sundog" that is around a sun that is low in the sky. This causes the majority of the rainbow to be "below the horizon" - so you only see a part of the circle (an arc).

BTW - if you've never seen a sundog, try on a day when there are a few cirrus clouds in the sky. These are really high in the atmosphere and are made of ice. Sometimes the circle is very close to the sun - only a few sunwidths wide. Sometimes they seem to take up most of the sky. Sometimes these wider ones look like rainbows, the colors aren't as brilliant, but they can still be distinguished.

The same thing happens with the moon (moondogs).

• Arasan
Lv 7

The rainbow forms when the sun's rays which are refracted(into different colours) and reflected by rain drops reach our eye at a particular angle(about 42 degrees for primary rainbow and about 51 degrees for secondary rainbow).According to simple geometric principles,the rain drops which lie at this particular angle and direction opposite to the sun lie in the form of a full circle or a part of it (arc).Even if there are enough rain drops to form a full circle,to an observer on the earth's surface,it will look like an arc only as it is limited by horizon.When the sun is near the horizon,an observer on a high mountain or on a plane will be able to see the whole circle of the rainbow.

rainbows are arcs of coloured light formed when the Suns rays are reflected and refracted (bent) by drops of water in the air - falling rain or spray. the colours in rainbows are red, orange, yellow, green, blue, indigo and violet. a rainbow with red on the outside and violet on the inside is called a primary bow. sometimes, the light is reflected twice and the colours are reversed in a secondary bow.

only half of a rainbow is visible, the lower half being cut off by the ground. a complete circle can be seen from an aeroplane.

Light from the sun bounces off raindrops at a certain angle so if the earth didn't get in the way rainbows would be completely circular. The angle is the same whether you look up down left or right hence the circle and hence the bow.

• DRD
Lv 4

Rainbows aren't round, the are areas where light is being refracted.

They just look round because of your point of view the way the light is being refracted to where you are viewing it. That's why they look like they move if you move. That other area had the refraction all along, but you didn't is it till you move to the new area.

They aren't moving, you are and you are seeing new areas of refraction.

If you were up high, they would look round.

• cafff
Lv 4

im guessing because of the earths gravitional field, rainbows are arched the same way that the earth is round

• Ozzy D
Lv 5

its all to do with the way light is refracted off the tiny wtaer droplets