Rainbows! shape of...diameters?

Question

What determines the arc of a rainbow?

Some rainbows appear almost semi-circular whilst others appear almost wider and flatter.

Any ideas??

Answer 1

Position of the sun.  The higher the sun, the "shorter" & flatter the rainbow.  The lower the sun, the "taller" & "rounder" the rainbow appears.  It's always directly opposite the sun...if there wasn't ground in the way & nothing but sky, it could look like a full circle.  

You can test this using a hose on a sunny day from a deck!

Answer 2

Rainbows are always circular. The arc would be dependant on how high the water droplets are refracting the sunlight. This can vary. Keep in mind that no two people see the same rainbow since it's an optical effect depending on where you're viewing it from. Even a few feet can make a difference (although not a big one).  

Answer 3

Position of the sun is the main factor. Rainbow is a complete circle located opposite the sun. The horison hides the lower half of the rainbow from you. When the sun is higher, most of the rainbow is below the horison and you only see the tip of it. When the sun is lower, you can see more of the rainbow.

From certain points of observation, you can see a complete circle.

Answer 4

Rainbows are always opposite the sun and their centres are below the horizon at the the antisolar point. The lower the sun the higher is the bow.

At sunrise or sunset a rainbow's centre, the antisolar point, is on the horizon. The rainbow is half in the sky, a semicircle. As the sun rises the bow's centre sinks. Eventually when the sun is 42º high only the tip of the bow is visible above the horizon. In the summer, rainbows are best seen in early morning or late afternoon when the sun is comparatively low.

Parts of a bow can often be seen below the horizon against a backdrop of fields or the ground. A more complete circle is sometimes visible from mountains or aircraft

A bow's appearance depends on drop size. The best are narrow ones with intense colours and these are made by large drops several mm in diameter. Look for them during very heavy showers.

Smaller drops produce broader bows with less saturated colours. Very small drops give nearly colourless cloudbows and fogbows.