A fish looks upward at an unobstructed overcast sky. What total angle does the sky appear to subten?(Take refractive index of water as `sqrt(2).)`

An under water swimmer looks upward at an unobstructed overcast sky. The vertex angle does the sky appear to subtend at the eye of swimmer is (critical angle for water air interface is C)

What colour does the sky appear to an astronaut ?

What is the critical angle for materail of refractive index sqrt 2 ?

What is critical angle for a material of refractive index sqrt(2) ?