Big Rainbow

If the viewer was looking from a peak or an airplane, he would be able to see most of or even the full circle of the rainbow. Since the full circle of the rainbow is directly opposite of the sun, almost half of the rainbow would be visible above the ground level only near sunrises and sunsets. It would appear tallest during mornings and evenings.

The half angle of the cone of the rainbow, which always appears perfectly circular, is constant at about $42 °$ from its center, as seen by a viewer. So it's never taller than about $42 °$ above the ground, if seen from ground level. Unless one is fortunate to see a double rainbow.

A rainbow is actually a cone with your eye at the vertex. The more rain with the sun hitting it you look across, the brighter the rainbow (this is why its easier to see a rainbow in the sky than when looking at a tree -- more distance.)

The axis of this cone is parallel to the suns rays. If the sun is too high, the rainbow will be more on the ground or trees, not in the sky.

Note: Where I live the storms almost always come from the west so later afternoon is the time to see rainbows is after the small summer storms have swept over leaving sun behind. In the morning you can see rainbows at the beginning of the storm, but these types of showers are not common early in the day.

• During afternoon time light rays travel in a straight line and hence the angle of deviation of spectrum band after refracting from water droplets is less. As a result, the rainbow formed is not large.
• During morning and after time the sun is at inclination so the light rays travel with some angle and hence the angle of deviation of spectrum band after refracting from water droplets is large. As a result, the rainbow formed is large.

Note : The rainbow formed is largest when the light rays are incident at an angle more than $49^\circ$ as it is the critical angle for water.

The sunlight is most refracted during the morning and evening because of the earth's curvature; this is what causes the rainbow to appear taller during the morning/evening. At least that's what I thought before reading the other solution choices.

If you don't KNOW, don't comment. Guesses are OBVIOUS. You fool NO ONE !! If you ever wonder why people avoid you, why they won't even say hello to you, quit wondering! This is the reason, right here!

I did it in my science lesson

Its a a better angle because rainbows occur when water vapor is present and light i is passing through some were around 45 degrees.