When you think of a rainbow, you probably imagine the colors red, orange, yellow, green, blue, and violet. This sequence is often remembered by the acronym ROYGBV. But have you ever wondered why these specific colors are chosen and what happened to indigo?
Isaac Newton was the first to study rainbows scientifically. When he used a prism to split light, he labeled the colors as red, orange, yellow, green, blue, indigo, and violet. However, what he called “blue” is what we might today call cyan or teal, similar to the color of the sky. The color we now refer to as blue, Newton called violet, like in the phrase “roses are red, violets are blue.”
Newton included indigo to make the number of rainbow colors match the seven notes of the Western musical scale: do, re, mi, fa, so, la, ti. But in reality, indigo is not as distinct as the other colors, which is why it’s often left out today.
Interestingly, purple and magenta don’t appear in a rainbow created by a prism. These colors are made by mixing red and blue light, which are on opposite sides of the rainbow. So, they don’t naturally overlap in a prism-created rainbow.
Sometimes, rainbows in the sky seem to have purple. This can be an optical illusion where deep blues surrounded by lighter colors look purplish to our eyes. However, purple can actually appear due to a phenomenon involving “supernumerary rings.” These rings are additional, fainter rings of color caused by light interference within raindrops.
When raindrops are the right size, the first red supernumerary ring can overlap with the main dark blue ring, creating purple. This is why you might see purple in a rainbow, even though it’s not part of the traditional color sequence.
So, next time you see a rainbow, remember that the colors you see are more than just a simple arc in the sky. They’re a fascinating blend of science and perception, with a bit of history thrown in. As the saying goes, “roses are red, violets are blue, and purple in a rainbow is a supernumerary hue.”
Gather a glass prism and a flashlight. In a dark room, shine the flashlight through the prism onto a white surface. Observe the spectrum of colors that appear. Try to identify each color and note any differences from the traditional ROYGBV sequence. Discuss why some colors might appear differently.
Using colored lights or digital tools, experiment with mixing red and blue light to create purple and magenta. Explore why these colors don’t appear in a natural rainbow. Reflect on how light mixing differs from pigment mixing.
Research the history of rainbows and how different cultures interpret them. Create a presentation or poster that includes the scientific explanation of rainbows and cultural myths or stories. Share your findings with the class.
Explore the connection between the seven colors of the rainbow and the seven notes of the Western musical scale. Create a musical piece or soundscape that represents each color. Present your composition and explain the choices you made for each color.
Investigate optical illusions related to color perception. Create or find examples of illusions where colors appear differently based on their surroundings. Discuss how these illusions relate to the appearance of purple in rainbows.
Rainbow – A meteorological phenomenon that is caused by reflection, refraction, and dispersion of light in water droplets, resulting in a spectrum of light appearing in the sky. – After the rain stopped, a beautiful rainbow appeared, displaying a range of colors across the sky.
Colors – Different wavelengths of light that are perceived by the human eye as distinct hues. – The colors of the rainbow include red, orange, yellow, green, blue, indigo, and violet.
Light – Electromagnetic radiation that is visible to the human eye and is responsible for the sense of sight. – Light travels faster than anything else in the universe, allowing us to see objects almost instantaneously.
Prism – A transparent optical element with flat, polished surfaces that refract light. – When white light passes through a prism, it is separated into its constituent colors, creating a spectrum.
Newton – A unit of force in the International System of Units (SI), named after Sir Isaac Newton, who formulated the laws of motion and universal gravitation. – The force required to accelerate a 1-kilogram mass by 1 meter per second squared is equal to one newton.
Indigo – A deep and rich color that is one of the seven colors of the rainbow, located between blue and violet. – Indigo is often used to describe the color of the night sky just after sunset.
Purple – A color intermediate between red and blue, often associated with royalty and nobility. – In physics, purple is not a spectral color but a combination of red and blue light.
Optical – Relating to sight or the behavior of light. – Optical instruments like microscopes and telescopes help us observe objects that are too small or too far away to see with the naked eye.
Phenomenon – An observable event or occurrence that can be studied scientifically. – The Northern Lights are a natural phenomenon caused by the interaction of solar wind with the Earth’s magnetic field.
Supernumerary – Referring to additional or extra features, often used in the context of optical phenomena like rainbows. – Supernumerary rainbows are faint, extra arcs that appear inside the main rainbow, caused by the interference of light waves.
