Question

Stars twinkle due to :

• A. atmospheric refraction
• B. scattering
• C. dispersion
• D. none of these

Hint:

Stars are point sources of light very far away. Their light travels through Earth's atmosphere, which has constantly changing density and temperature. This causes the starlight to bend (refract) randomly in different directions. As a result, the amount of light reaching our eyes flickers, and the star's apparent position seems to waver slightly. This is twinkling. Key: {Atmospheric Refraction}.

Answer 1

The Correct Option is A

Concept: The twinkling of stars is an optical phenomenon observed when viewing stars from Earth. It is caused by the interaction of starlight with the Earth's atmosphere. Step 1: Nature of Starlight and Earth's Atmosphere Stars are extremely distant, so they appear as point sources of light. Earth's atmosphere is not uniform; it consists of layers of air with continuously varying temperatures and densities. This variation causes the refractive index of the air to fluctuate randomly from point to point and over time due to atmospheric turbulence (air currents, wind). Step 2: Atmospheric Refraction Refraction is the bending of light as it passes from one medium to another, or through a medium of varying optical density. As starlight enters and passes through Earth's atmosphere, it encounters these layers of air with different refractive indices. This causes the starlight to be continuously refracted (bent) by small, random amounts. Step 3: Effects of Random Refraction
Apparent Position Shift: The continuous and random bending of the light path makes the apparent position of the star seem to shift slightly and fluctuate.
Brightness Variation: The path of the light rays reaching the observer's eye changes continuously. Sometimes more light rays are directed towards the eye, making the star appear brighter, and sometimes fewer rays reach the eye, making it appear dimmer. This rapid fluctuation in the apparent brightness and position of the star is perceived as twinkling. Step 4: Analyzing other options
(2) Scattering: Scattering of light by atmospheric particles (like air molecules or dust) is responsible for phenomena like the blue color of the sky (Rayleigh scattering) or the white appearance of clouds (Mie scattering). While scattering affects starlight, it's not the primary cause of the twinkling effect (rapid brightness/position changes).
(3) Dispersion: Dispersion is the splitting of white light into its constituent colors (like in a prism or rainbow) due to the wavelength dependence of the refractive index. While starlight undergoes some dispersion, it's not the main reason for twinkling.
(4) none of these: Incorrect, as atmospheric refraction is the cause. Therefore, the twinkling of stars is primarily due to atmospheric refraction.