Neil deGrasse Tyson Explains Why The Sky Is Blue

Summary

In this engaging explanation, the concept of why the sky is blue is explored in a fun and accessible way. The video delves into the science behind Rayleigh scattering, where blue light from the Sun gets scattered more than other colors due to its shorter wavelength. As the Sun sets, the sky changes color because blue light is scattered away, leaving red and orange hues. The video also touches on the fragility of Earth's atmosphere, comparing it to the skin of an apple, highlighting the importance of protecting it. The discussion concludes with a reflection on the operational definition of space and the delicate balance sustaining life on Earth.

Takeaways

• 😀 The sky is blue due to Rayleigh scattering, where shorter wavelengths of light, particularly blue, scatter more than longer wavelengths like red.
• 😀 White light from the Sun contains all the colors of the visible spectrum (ROYGBIV), and is composed of red, orange, yellow, green, blue, indigo, and violet.
• 😀 Blue light scatters in all directions because particles in Earth's atmosphere are similar in size to the wavelength of blue light.
• 😀 During the day, the sky appears pale blue because the Sun's light path is short, and the scattering effect is weaker.
• 😀 At sunset, the sky can turn red or orange because the longer path of light scatters much of the blue, leaving the warmer colors behind.
• 😀 We cannot see stars during the day because the scattered blue light causes the atmosphere to glow, blocking the stars from view.
• 😀 The operational definition of space is based on the altitude where blue light scattering stops, roughly 62 miles (100 kilometers) above Earth's surface.
• 😀 If Earth's atmosphere were thinner, we would be able to see stars much closer to the ground—this defines the edge of space.
• 😀 The atmosphere is incredibly thin compared to Earth's size—its thickness is comparable to the skin of an apple.
• 😀 Protecting Earth's atmosphere is crucial, as it's fragile and essential to sustaining life on our planet.

Q & A

Why is the sky blue?

The sky appears blue due to Rayleigh scattering, where shorter wavelengths of light (like blue) scatter more easily in the atmosphere compared to longer wavelengths (like red). This scattering causes the blue light to be dispersed in all directions, making the sky appear blue.

What is Rayleigh scattering?

Rayleigh scattering refers to the phenomenon where light is scattered in different directions by particles in the atmosphere. It occurs more strongly with shorter wavelengths (like blue), which is why the sky appears blue.

Why does the sky appear red during sunset?

During sunset, the Sun's light path through the atmosphere is longer, causing more scattering of blue light. As a result, the red, orange, and yellow wavelengths become more dominant, giving the sky a reddish hue.

Why can't we see stars during the day?

Stars are not visible during the day because the scattered blue light from the Sun causes the sky to glow. This glow makes it difficult to see the dimmer light from stars.

What causes the Sun to appear white instead of yellow?

The Sun actually emits white light, which is a mix of all colors of the visible spectrum. The yellow appearance is a result of atmospheric scattering, but in the middle of the day, the Sun's light is white.

What is the operational definition of space?

The operational definition of space is set at 62 miles (100 kilometers) above the Earth's surface. This is where the atmosphere is thinned out enough that blue light no longer scatters, allowing the night sky to be visible even in broad daylight.

Why is Earth's atmosphere compared to the skin of an apple?

Earth's atmosphere is very thin compared to the size of the planet, just like the skin of an apple is thin compared to the fruit inside. This comparison emphasizes the fragility and importance of the atmosphere in sustaining life.

What happens if Earth's atmosphere is thinner?

If Earth's atmosphere were thinner, the boundary of space would be much lower. For example, if the atmosphere were half as thick, space would begin at 31 miles instead of 62 miles. This highlights the delicate balance of the atmosphere.

Why is the atmosphere essential for life on Earth?

The atmosphere is crucial for life because it provides oxygen, protects from harmful radiation, and maintains a stable climate. Its thinness makes it vulnerable, which is why it must be protected.

How does the density of particles affect the visibility of stars?

The density of particles in the atmosphere causes the scattering of light, which is why blue light makes the sky glow. When the atmosphere thins, such as in space, stars become visible because there are fewer particles to scatter light.