why the rainbow comes?

The rainbow effect can be observed whenever there are water drops in the air and sunlight shining from behind the observer at a low altitude or angle. The most spectacular rainbow displays when half of the sky is still dark with draining clouds and the observer is at a spot with clear sky overhead. The rainbow effect is also commonly seen near waterfalls or fountains. Rainbow fringes can sometimes be seen at the edges of backlit clouds and as vertical bands in distant rain or virga. The effect can also be artificially created by dispersing water droplets into the air during a sunny day.

In a very few cases, a moonbow, or night-time rainbow, can be seen on strongly moonlit nights. As human visual perception for colour in low light is poor, moonbows are perceived to be white.

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°, regardless of the size of the drop. Since the water of the raindrops is dispersive, the amount that the sunlight is bent depends upon the wavelength, and hence colour, of the light's constituent parts. Blue light is refracted at a greater angle than red light, but because the area of the back of the droplet has a focal point inside the droplet, the spectrum crosses itself, and therefore the red light appears higher in the sky, and forms the outer colour of the rainbow. Contrary to popular belief, the light at the back of the raindrop does not undergo total internal reflection; however, light that emerges from the back of the raindrop does not create a rainbow between the observer and the Sun. The spectra emitted from the back of the raindrop do not have a maximum of intensity, as the other visible rainbows do, and thus the colours blend together and do not form a rainbow.

What a perfect question for highlighting different pholosophies: science and religion.

A message from god to show he won't ever flood the world again.
Well that's nice to know, but if you believe he was OK with wiping out the world's population how can you believe that he won't tell a lie? Mass murder or telling a lie, Hmm difficult choice...

Science: here's the facts and we can prove them. I know which I believe in.

about the weather* ??

light is reflected off the rain through the sun

it is light passing through water droplets and breaking up. The water acts like a prism and separates the different colors within the light. the round shape of the rainbow is actually created by your eyeball.

the rain came fokes is sun light and make the rainbow...............

God created the rainbow after the great flood as His promise that the world would never flood again.

thers a rainbow always after the rain

B/c god shows us that there will never be a great flood ever again.