Why did the sun go to school?

This joke brightens the mood by relying on a clever bit of wordplay, specifically the dual meaning of the word "brighter." When we send someone to school, the goal is for them to become intellectually "brighter," gaining knowledge and understanding. However, when applied to our star, the sun, "brighter" takes on its literal meaning, referring to the intensity of its radiant light. The humor comes from this playful twist, applying a human concept of learning and improvement to a celestial body that is already the ultimate source of literal illumination.

It's a classic example of personification, where a non-human entity like the sun is given human-like actions and motivations. While our actual sun doesn't attend classes to enhance its already powerful glow, the image of it doing so is charmingly absurd. We understand the pursuit of knowledge, and seeing the sun as a cosmic student makes the joke relatable, even if its "lessons" are more about nuclear fusion than arithmetic, constantly emitting immense amounts of light and energy.