• The Sun is like a gigantic nuclear reactor! It's doing nuclear fusion reactions and spitting out enormous amounts of energy every second.
• Earth, being a little blue dot in the vastness of space, only receives a tiny portion of this energy because it's quite far from the Sun.

Real-world Example: Imagine you're in a stadium and someone's taking a picture from the opposite side with a super bright flash. You'd see the flash, but it wouldn't blind you because you're so far away. Similarly, the Sun is immensely bright, but due to Earth's distance, we only get a fraction of that energy.

• A black body at the Sun's temperature emits
  • Just under 50% of its energy in the visible region (what our eyes see)
  • Roughly 50% in the infrared (feeling of warmth)
  • About 10% in ultraviolet (yes, that's why we need sunscreen!)

Real-world Example: When you wear black on a sunny day, you feel hotter. Black absorbs all wavelengths (colors) effectively, and hence we can relate the absorption of sunlight by black objects to the radiation of a black body!

The energy we get from the Sun is crucial! It's responsible for

• Plants doing photosynthesis 🌱
• Driving atmospheric and oceanic changes 🌊
• Literally powering life on our planet! 💡

• Intensity I is the power P arriving per unit area A:I = \(\frac PA\)​.
• The solar constant S is the intensity of solar radiation at Earth's distance from the Sun, hitting a surface perpendicular to the line joining Earth's and Sun's centers.

Real-world Example: Imagine the Sun as a giant flashlight. Its brightness (or power) spread over a certain area determines its intensity. When that flashlight is directed at Earth from its average distance, the intensity we get is the solar constant!