The sky appears dark to passengers flying at very high altitudes mainly because :

Options

A. Scattering of light is not enough at such heights
B. There is no atmosphere at great heights.
C. The size of molecules is smaller than the wavelength of visible light.
D. The light gets scattered towards the earth.

Answer

To solve the question "The sky appears dark to passengers flying at very high altitudes mainly because:", we can follow these steps:

### Step 1: Understand the phenomenon of light scattering
At lower altitudes, the atmosphere is denser, and light from the sun interacts with air molecules. This interaction causes scattering, which is why we see the sky as blue from the ground. The shorter wavelengths of light (blue) scatter more than the longer wavelengths (red).

**Hint:** Remember that light scattering is responsible for the color of the sky we see from the ground.

### Step 2: Analyze the conditions at high altitudes
As we ascend to higher altitudes, the density of the atmosphere decreases significantly. There are fewer air molecules for the sunlight to scatter off. This means that the scattering effect is reduced.

**Hint:** Consider how the density of the atmosphere changes with altitude and how that affects light scattering.

### Step 3: Determine the color of the sky at high altitudes
At very high altitudes, where the atmosphere is thin, there is minimal scattering of light. Without significant scattering, the sky does not appear blue; instead, it appears dark or black, as the actual color of the sky is revealed.

**Hint:** Think about what happens to the light when there are fewer particles in the air to scatter it.

### Step 4: Conclusion
Therefore, the sky appears dark to passengers flying at very high altitudes mainly because there is less atmosphere to scatter the sunlight, revealing the true color of the sky, which is dark.

**Final Answer:** The sky appears dark at high altitudes because there is less atmosphere to scatter sunlight.