Why is a rainbow curved?
A rainbow is curved because of the way that light shines - it
forms into a curved shape.
A rainbow is curved because the light that makes it up comes
through the atmosphere
which is curved around the planet, it includes every colour of
the light spectrum.
A rainbow is curved because at every point on the rainbow, the
angle between the
line to the sun and the line to you has to be 42 degrees ... at
any other angle, the
light leaving the water droplet misses you and you don't see
A great number of points where that angle is true form a
(Of course, only the ones that are above the ground can
participate in the process.
The ones that are underground either can't see the sun or can't
see you, and there's
probably no water droplets there anyway, so there's no path for
the light to go from
the sun to the point underground and then to you, and you don't
see a full circle.)