The correct option is 1, 2 and 4.
Explanation
Optical illusions arise due to the bending of light (refraction), scattering, or atmospheric effects that alter the apparent perception of celestial objects.
- Size of the sun at dusk: Correct.
The apparent enlargement of the sun near the horizon is an optical illusion caused by atmospheric refraction and perceptual effects, not an actual change in size. - Colour of the sun at dawn: Correct.
The reddish appearance of the sun at dawn is due to scattering of shorter wavelengths of light by the atmosphere, making longer wavelengths (red/orange) more prominent. - Moon being visible at dawn: Incorrect.
The visibility of the moon at dawn is a natural astronomical phenomenon based on its position relative to the Earth and the Sun, not an optical illusion. - Twinkle of stars in the sky: Correct.
Twinkling of stars is caused by atmospheric refraction due to varying air densities, which makes starlight appear to fluctuate. - Polestar being visible in the sky: Incorrect.
The visibility of the Polestar is due to its fixed position near the celestial pole and is not an optical illusion.
Key Takeaway: Optical illusions in astronomy are mainly caused by atmospheric effects such as refraction and scattering, leading to apparent changes in size, color, or brightness.