When the Sun is near the horizon during the morning or evening, it appears reddish. The phenomenon that is responsible for this observation is
Scattering of light
Understanding Why the Sun Appears Reddish at Sunrise and Sunset
The fascinating phenomenon where the Sun appears reddish when it is near the horizon during the morning (sunrise) or evening (sunset) is a common observation. This striking color change is primarily caused by how sunlight interacts with the Earth's atmosphere, specifically through a process called scattering of light.
The Role of Scattering of Light at the Horizon
Sunlight is a mixture of different colors, each corresponding to a different wavelength. When sunlight travels through the atmosphere, it encounters various tiny particles like molecules of air (nitrogen and oxygen), dust, and water vapor.
- Rayleigh Scattering: This type of scattering is most significant for particles that are much smaller than the wavelength of light, such as air molecules. Rayleigh scattering is more effective for shorter wavelengths (like blue and violet light) than for longer wavelengths (like red and orange light). Essentially, blue light is scattered in all directions much more strongly than red light.
During midday, when the Sun is high overhead, the sunlight travels a relatively short distance through the atmosphere. While some blue light is scattered, enough light of all wavelengths reaches our eyes directly, making the Sun appear yellowish-white. The scattered blue light is what makes the sky appear blue.
Explaining the Reddish Sun at Sunrise and Sunset
When the Sun is near the horizon during sunrise or sunset, sunlight has to travel a much longer distance through the atmosphere to reach our eyes compared to when the Sun is overhead. As the light travels this longer path:
- A significant amount of the shorter wavelength light (blue and violet) is scattered away by the atmospheric particles.
- The longer wavelength light (red and orange) is scattered much less effectively and therefore manages to travel through the atmosphere and reach our eyes.
This filtering effect means that the light we see coming directly from the Sun at sunrise or sunset is predominantly composed of longer wavelengths, making the Sun appear reddish or orange.
Analyzing the Options
Let's look at the given options:
- Reflection of light: This is the bouncing of light off a surface. While reflection occurs in the atmosphere (e.g., from clouds), it is not the primary reason for the Sun's reddish appearance at the horizon.
- Refraction of light: This is the bending of light as it passes from one medium to another (like different layers of air with varying densities). Refraction causes the Sun to appear distorted or slightly higher or lower than its actual position, but it doesn't explain the distinct reddish color.
- Dispersion of light: This is the splitting of white light into its constituent colors, as seen in a rainbow or prism. While sunlight is composed of different colors, the atmosphere doesn't act like a prism to disperse the light and present only red light to our eyes. Scattering is the process that removes other colors.
- Scattering of light: As explained above, this is the process where light is absorbed and re-emitted by particles, causing it to spread out in different directions. The differential scattering of wavelengths (Rayleigh scattering) is precisely what causes the shorter wavelengths to be removed from the direct path of sunlight when it travels a long distance through the atmosphere, leaving the longer, reddish wavelengths to dominate the Sun's appearance.
Therefore, the phenomenon responsible for the reddish appearance of the Sun near the horizon is scattering of light.
| Phenomenon | Description | Relevance to Reddish Sun |
|---|---|---|
| Reflection | Light bouncing off surfaces. | Not the primary cause of color change. |
| Refraction | Bending of light through different media. | Causes positional/shape distortion, not the reddish color. |
| Dispersion | Splitting of light into colors. | Atmosphere doesn't primarily disperse light like a prism to cause this effect. |
| Scattering | Light interacts with particles, spreading out. Different wavelengths scatter differently. | Yes, differential scattering removes shorter wavelengths, leaving red/orange light visible from the direct path when light travels a long distance. |
Revision Table: Understanding Light Phenomena
| Term | Simple Explanation | Example |
|---|---|---|
| Reflection | Light bouncing back. | Seeing your face in a mirror. |
| Refraction | Light bending as it passes into a new material. | A spoon appearing bent in a glass of water. |
| Dispersion | Splitting white light into colors. | A rainbow or light through a prism. |
| Scattering | Light hitting particles and spreading out. | Why the sky is blue, why clouds are white, the reddish sun at sunset. |
Additional Information on Atmospheric Scattering
While Rayleigh scattering is the main reason for the blue sky and reddish sun phenomena, other types of scattering also occur in the atmosphere:
- Mie Scattering: This occurs when light interacts with larger particles, such as dust, pollen, or water droplets. Mie scattering is less dependent on wavelength, which is why clouds (made of water droplets) appear white (all colors are scattered equally).
- The combination of Rayleigh scattering and Mie scattering, along with absorption by gases and aerosols, determines the overall appearance of the sky and the colors of the Sun and clouds under various conditions.
- The intense colors at sunrise and sunset are often enhanced by increased atmospheric particles like dust or pollution, which can increase the scattering effect, especially for longer wavelengths at very low angles.
Similar Questions
In a periscope, the two plane mirrors are kept
Light travels in a straight line (rectilinear propagation of light). This statement does hold if the medium of travel for light is
A myopic person has a power of -1.25 Dioptre. What is the focal length and nature of his lens?
- In a simple astronomical telescope, the objective and the eyepiece used respectively, are:
Which of the following combinations of source and screen would produce the sharpest shadow of an opaque object?
In total internal reflection, the light travels from ________.
The energy of a photon, whose momentum is 10 MeV/c, where c is the speed of light, is- given by
If an object is placed at the focus of a convex lens, its image is
Which one of the following is the correct sequence of passage of light in a compound microscope?
Where should an object be placed in front of a convex lens to get a real and enlarged image of the object ?
Important Questions from Optics
Who was the first one to use a glass prism to obtain the spectrum of sunlight?
Twinkling of stars is due to:
In which a convex mirror is used?
A. Rear View mirrors in vehicles
B. Glass windows
C. Makeup Mirror
D. Kaleidoscope
An object is placed 10 cm in front of a lens. The image formed is real, inverted and of same size as the object. What is the focal length and nature of the lens?
The power of a lens is -2.5 D. The type of lens and its focal length are respectively:
