Why is a rainbow a perfect arc.... is it because the earth is round or the Sun ?

Question

Yeah I'm cool with those explications BUT a raindrop in 'slightly' pear shaped. And if I refract light through a perfectly round glass ball the sple of the arc is either round, eliptical or oval depending where i put my light source... so no doesnt' really answer my question, But thanks anyway...i'll dream some more

Answer 1

A rainbow is refracted light. That means the light from the sun is bent when it passes through the raindrops of water,  like the images you see when you try to look thru a glass of water.  Each color that makes up the white light bends a little different thus separating into the colors of the rainbow.  The light is bent at a precise angle (think it is 60 degrees) based on the make up of the water atoms in the water molecule.  The arc you see is the locus of points that are 60 degrees from the straight on view of the light.  They would form a full circle if not for the horizon (land)

The light also refracts at higher angles (I am thinking 80 and 120 degrees) but with less intensity.  That is why you will occasionally see a double rainbow.  And far less frequently a triple rainbow.

Answer 2

A rainbow well,  it would actually form a complete circle if there weren't any land below. Thats actually what you see from a plane(sounds cool doesn't it?), so what you see is part of a circle it forms a complete circle because the light from the raindrop(which acts like a prism) deviated/internally reflects it that way. So since the circle is formed because of the raindrop, then I guess the arc( which is part of the circle) is formed because of the raindrop deviating it like that. Hope it helps!

------------------------------ EDIT--------------------------...

You say when you refract light through a sphere it is round (circle)as i said the RAINBOW ACTUALLY IS A CIRCLE.

But we see only half of it, hence appearing like an arc or semi-circle, if the horizon was lower we would see the rest of the ACTUALLY CIRCLE SHAPED RAINBOW WHICH GETS HIDDEN BY THE HORIZON. So incase you want proof, when you see a rainbow from  an airplane, it is actually appearing like a circle. Hope you understand now, but never stop dreaming...hehe. Peace-Out.

Answer 3

Each color emerges at a slightly different angle on each raindrop. When millions of raindrops gather, the spectrum shows up as distinct bands of color - each with a different length. Red is the longest and violet the shortest band. The arc is most pronounced when the Sun is close to the horizon.

Ok hope that answered your question!

Answer 4

Because a rainbow is really an angle from the sun, which must be behind you, and your line of sight, which extends out in front of you.

The sun's rays shine past you, from behind, and then hit raindrops in front of you, where much of the light is reflected, broken up into (a prism-like) set of colours back towards you. But only those at the correct angle get reflected back to your eye. -All the rest are reflected back past you. So these (reflected ) ones you can actually see, appear as a circle.

If you can see it all -like when you're up in a plane looking down to the ground- then you see a full, complete circle.

But if you're on the ground, you usually can see just an arc of the full circle.

Answer 5

It's the curvature of the earth.

Answer 6

Each person far apart sees a different rainbow from their own point of view.  When you see a 'rainbow' in the mist of a sprinkler system it is a round circle because the tiny droplets of water break up the light into a range of wavelengths (colors) and you see only one color from all the drops that are at a given angle with respect to the sun light, water drop and you.  If the sun were directly overhead, you would see complete concentric circles of color.  But with the sun at the usual angle you see only an arc above the ground.

Answer 7

never wondered why!

Answer 8

Neither- the rainbow's appearance is caused by dispersion of sunlight as it is refracted by (approximately spherical) raindrops. The light is first refracted as it enters the surface of the raindrop, reflected off the back of the drop, and again refracted as it leaves the drop. The overall effect is that the incoming light is reflected back over a wide range of angles, with the most intense light at an angle of about 40-42 degrees. The different colours (wavelengths) of light have different refractive indices which cause them to bend unequally. Thus, a rainbow is arc-shaped.

Answer 9

neither

it is because the raindrops are spherical (actually elongated spheroids).....light has to be refracted at a certain angle, from the point of view of an observer, for them to see a rainbow.

if you have a single light source (sun), and a single point of observation (eye), then the raindrop (prism) has to be in a particular area for the refracted light to reach the eye.

if the ground did not get in the way, the area would be a perfect circle, centred on a line between the sun and eye