6.1
The Earth and the Solar System
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Why we have day and night, seasons, and Moon phases — plus our entire Solar System. Earth's rotation and tilted axis, orbital motion around the Sun, the Moon's monthly cycle, the eight planets in order, rocky vs gaseous worlds, the accretion model, gravitational fields, light travel time, elliptical orbits, orbital speed (v = 2πr/T), and conservation of energy in orbits.
6.2
Stars and the Universe
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From our Sun to the edge of the observable Universe. The Sun as a medium-sized star powered by hydrogen fusion, galaxies containing billions of stars, the Milky Way, measuring distances in light-years, the complete life cycle of stars (protostar → main sequence → red giant or supergiant → white dwarf, neutron star, or black hole), redshift, the expanding Universe, Big Bang Theory, cosmic microwave background radiation, and the Hubble constant (H₀ = v/d).