Optical illusions in nature

Optical illusions among these: (1) Moon/sun appearing larger at horizon—Moon illusion caused by atmospheric refraction and relative comparison (optical illusion). (2) Sun appearing reddish at dawn/dusk—caused by Rayleigh scattering of shorter blue wavelengths, leaving longer red/orange wavelengths (optical effect/illusion). (3) Moon visible at dawn is real phenomenon, not an illusion—moon actually present in sky. (4) Stars twinkling—caused by atmospheric turbulence creating real fluctuations in light intensity (optical effect). (5) Polestar visible—real astronomical fact, not illusion. The question specifically asks for optical illusions. Items 1 and 2 are perceptual illusions caused by atmospheric effects and human visual system. Item 4 (twinkling) is sometimes debated but is a real physical phenomenon. > Illusions vs Reality: Moon size (illusion), Sun color (illusion), Star twinkle (real physical effect), Polestar (real).