Astronomy and the Earth–Moon–Sun System
Earth's motions and seasons
Earth rotates west-to-east on an axis tilted 23.4°, producing day and night; revolution with that fixed tilt produces seasons. Seasons are not caused by distance - Earth is nearest the Sun in early January. At a solstice one pole tips toward the Sun; at an equinox the terminator passes through both poles, giving roughly 12 hours of daylight everywhere. Solar noon altitude = 90° − |latitude − solar declination|; this single formula answers most shadow and sun-angle questions.
Moon, phases, and eclipses
The Moon rotates and revolves in the same period (synchronous rotation), so one face always points at Earth. Phases come from the changing viewing geometry of the sunlit half, not from Earth's shadow. New moon → solar eclipse; full moon → lunar eclipse; both require the Moon near a node because its orbit is inclined about 5° to the ecliptic. The synodic month (phase to phase, ~29.5 days) is longer than the sidereal month (~27.3 days) because Earth moves along its orbit. Spring tides occur at new and full moon, neap tides at the quarters.
Beyond the Earth–Moon system
Know Kepler's laws (elliptical orbits, equal areas in equal times, P² ∝ a³), Newton's gravitation, the electromagnetic spectrum, Wien's law, and the inverse-square law. The solar system formed from a collapsing nebula: rocky planets inside the frost line, gas and ice giants outside. Stars live out mass-dependent life cycles traced on the H-R diagram; parallax measures nearby distances; cosmological redshift supports an expanding Universe; a light-year is a distance.
Traps: "seasons occur because Earth is closer to the Sun"; "the far side of the Moon is the dark side"; "eclipses happen every month"; "a solar eclipse occurs at full moon." Rule of thumb: the phase name alone never predicts an eclipse - the Moon must also be near a node.
Worked example
At latitude 34°N on the June solstice (declination +23.5°), solar noon altitude = 90° − |34 − 23.5| = 79.5° above the horizon.