Weather Basic: Optics

Summary

This video explores the optical effects of the atmosphere, explaining how phenomena like rainbows, halos, sun dogs, and the aurora borealis are created. It discusses the role of water droplets and ice crystals in refracting and reflecting light, breaking it into its visible components. The video also addresses why clouds are white or gray, why the sky appears blue, and how light scattering changes during sunrise and sunset. Additionally, it explains how solar particles interact with the Earth's atmosphere to produce the colorful displays of the auroras, showcasing the beauty and science of atmospheric optical effects.

Takeaways

• 🌈 Rainbows are formed when sunlight enters raindrops, refracts, and reflects, breaking light into its component colors.
• 🌦️ To see a rainbow, you need rain in one part of the sky and sunshine in another, with the sun at your back.
• 💧 Each raindrop produces only one color of the rainbow due to specific refraction angles (40-42 degrees), making the rainbow unique for every observer.
• 🌟 A secondary rainbow appears outside the main rainbow due to two internal reflections inside raindrops, with colors in reverse order.
• ❄️ Halos form as light refracts through ice crystals in the atmosphere, typically from cirrus clouds, and can surround the sun or moon.
• ☀️ Sun dogs, or mock suns, are bright spots appearing around halos, about 22 degrees from the sun, due to light refraction through ice crystals.
• 🌞 Sun pillars are vertical beams of light that appear when sunlight reflects off ice crystals falling slowly through the air, often at sunrise or sunset.
• ☁️ Clouds appear white because water droplets scatter visible light, but darker clouds indicate higher density or larger droplets that absorb more light.
• 💡 The sky appears blue because shorter wavelengths of light (blue and violet) are scattered by air molecules, but our eyes are more sensitive to blue.
• 🌅 At sunrise and sunset, the sky turns red or orange as sunlight travels through more atmosphere, scattering shorter wavelengths and leaving longer ones.
• 🌌 The aurora borealis is caused by solar particles interacting with Earth's magnetic field, creating light displays, with oxygen and nitrogen causing green and red colors.

Q & A

What role does the atmosphere play beyond weather?

The atmosphere not only affects daily weather but also creates optical effects like rainbows, halos, sun pillars, and sun dogs when conditions are right.

Why do we see a rainbow after rain?

Rainbows form when sunlight enters water droplets, which act like prisms, refracting the light and splitting it into different colors. This occurs when rain is in one part of the sky and sunlight shines from the other.

Why don't we see colored light everywhere when light is refracted in water droplets?

The colors from light entering water droplets exit at specific angles between 40 to 42 degrees, which is why the rainbow appears as a distinct arc rather than random colored light across the sky.

What causes the secondary rainbow to appear?

A secondary rainbow forms when light undergoes two internal reflections within water droplets. This rainbow is fainter and has reversed colors, with red on the inside and violet on the outside.

How do halos form around the sun or moon?

Halos are caused by light refracting through ice crystals in the atmosphere, usually in cirrus clouds. The ice crystals bend the light, creating a ring around the sun or moon.

What are sun dogs and how do they form?

Sun dogs are bright spots that appear on either side of the sun, typically 22 degrees away. They form due to the refraction of light through ice crystals in the atmosphere, often appearing with halos.

What are sun pillars and when are they visible?

Sun pillars are vertical shafts of light that seem to emanate from the sun, visible when sunlight reflects off ice crystals falling slowly through the atmosphere, typically at sunrise or sunset.

Why do clouds appear white or gray?

Clouds appear white because the water droplets scatter all visible light. They turn gray or black when they become denser or contain larger droplets, absorbing more light.

Why is the sky blue, but not green or purple?

The sky appears blue because shorter wavelengths of light, like violet and blue, are scattered by air molecules. However, our eyes are more sensitive to blue, so the sky appears predominantly blue.

What causes the colors of the sky to change during sunrise and sunset?

At sunrise and sunset, the sun’s rays travel through more of the atmosphere, scattering shorter wavelengths like violet and blue, leaving longer wavelengths such as yellow, orange, and red to reach our eyes.

How are the auroras (Northern and Southern Lights) formed?

Auroras form when charged particles from the sun interact with oxygen and nitrogen molecules in Earth's atmosphere. The resulting collisions release light, creating colorful displays, most commonly greenish-white or red.

Why are auroras more visible in polar regions?

Auroras are typically seen near the poles because Earth's magnetic field directs solar particles toward these areas, where they collide with atmospheric molecules, creating auroras.