Secondary rainbow

Definition

A secondary rainbow is a fainter, outer arc of light that appears outside the primary rainbow, formed by the refraction, reflection, and dispersion of sunlight through water droplets in the atmosphere. This phenomenon occurs when light is refracted twice within a droplet before exiting, resulting in a reversal of colors compared to the primary rainbow. The secondary rainbow is typically seen when sunlight shines on water droplets after a rain shower, often in conjunction with the brighter primary rainbow.

5 Must Know Facts For Your Next Test

1. The secondary rainbow is typically located outside the primary rainbow and has its colors arranged in reverse order, with red on the inner edge and violet on the outer edge.
2. It is generally fainter than the primary rainbow due to the increased number of reflections inside the water droplets, which causes more light to be lost.
3. The angle at which light emerges from a secondary rainbow is around 50 to 53 degrees, compared to approximately 42 degrees for a primary rainbow.
4. Secondary rainbows are often accompanied by supernumerary rainbows, which are closely spaced additional arcs that appear inside the primary rainbow due to interference effects.
5. Viewing conditions for secondary rainbows require that the sun be low in the sky, such as during early morning or late afternoon, and that there be sufficient moisture in the air.

Review Questions

• How does the formation of a secondary rainbow differ from that of a primary rainbow?
  • The formation of a secondary rainbow involves two internal reflections within a water droplet as opposed to just one for a primary rainbow. This double reflection causes light to emerge at a different angle and results in reversed colors. While both types of rainbows occur from refraction and dispersion, the additional reflection in a secondary rainbow leads to its characteristic dimness and broader angular spread.
• Discuss why secondary rainbows are typically less bright than primary rainbows and what factors contribute to their visibility.
  • Secondary rainbows are less bright primarily because they involve more internal reflections, which leads to greater light loss. Each reflection disperses some light, resulting in diminished intensity. Factors like viewing angle, sunlight's position in the sky, and atmospheric conditions also play significant roles; optimal conditions can enhance visibility despite their natural dimness.
• Evaluate the role of atmospheric conditions in observing both primary and secondary rainbows and how these conditions influence their appearance.
  • Atmospheric conditions are crucial for observing both types of rainbows as they dictate the presence of water droplets and sunlight angles necessary for refraction. Secondary rainbows require moisture in the air, like after rainfall, and need sunlight positioned low on the horizon for optimal viewing. These conditions affect brightness and color arrangement; when conditions align properly, it can lead to stunning visual displays with multiple arcs visible in the sky.

Related terms

refraction: The bending of light as it passes from one medium to another, such as from air into water droplets, which is crucial for the formation of rainbows.

dispersion: The process by which different wavelengths of light are separated as they pass through a medium, leading to the formation of a spectrum of colors.

water droplet: A small spherical body of liquid water that acts as a prism in the atmosphere, playing a key role in the formation of both primary and secondary rainbows.