Why do you only see an arch in a rainbow?

A rainbow appears as an arch due to the way light refracts, reflects, and disperses in water droplets in the atmosphere. When sunlight enters a droplet, it bends (refracts), reflects off the inside surface, and then bends again as it exits, creating a spectrum of colors. The circular shape of the rainbow is a result of the angle at which light exits the droplet, typically forming a semicircle. However, we usually only see the upper half of this circle because the ground obstructs the lower half.