The Sun's light does travel in a straight line through space. However, when the Sun's light interacts with the Earth's atmosphere, it can undergo several phenomena that cause it to deviate from a perfectly straight path. Here are a few reasons why this happens:
Atmospheric Refraction: When light passes through the Earth's atmosphere, it encounters changes in the density of the air. These density variations cause the speed of light to change, which in turn leads to the bending of light rays. This bending is known as refraction. The Earth's atmosphere is composed of layers with varying densities, temperature, and humidity, and these variations can cause the Sun's light to refract as it passes through them, resulting in the apparent position of the Sun being slightly higher than its true position.
Scattering: The Earth's atmosphere contains particles such as dust, water vapor, and molecules of gas. These particles can scatter sunlight in different directions. Rayleigh scattering, for example, scatters shorter wavelengths of light (blue and violet) more than longer wavelengths (red and orange), which is why the sky appears blue during the day. The scattering of sunlight can cause it to spread out in different directions, leading to an apparent broadening or dispersion of the Sun's light.
Absorption and Reflection: The Earth's atmosphere can absorb and reflect certain wavelengths of light. For example, the ozone layer absorbs much of the Sun's ultraviolet radiation, while clouds reflect a portion of the sunlight back into space. These absorption and reflection processes can influence the path of light, although they do not significantly affect the overall direction of sunlight.
It's important to note that while these factors cause some deviation in the path of sunlight, they are relatively small and do not drastically alter the fact that light from the Sun travels in nearly straight lines over astronomical distances.