* Hypothesis: A hypothesis is a testable prediction or explanation for an observation. It needs to be falsifiable, meaning there needs to be a way to prove it wrong.

* Observation: The statement "the sky is blue" is a simple observation. It's something we can see and experience.

Why the sky is blue is a scientific explanation, not just a hypothesis.

* Explanation: Scientists have developed a detailed explanation for why the sky appears blue, based on the scattering of sunlight by molecules in the atmosphere. This explanation is supported by scientific evidence and experimentation.

In summary:

* "The sky is blue" is an observation.

* The explanation for why the sky is blue is a scientific theory.