Ask why summer is hot, and the most common answer is "Earth gets closer to the Sun." It's intuitive, confident — and wrong. Earth's orbit is very nearly circular, and Earth is actually at its closest point to the Sun (perihelion) in early January, right in the middle of Northern Hemisphere winter. It's at its farthest point (aphelion) in early July, during Northern Hemisphere summer — the exact opposite of what the myth predicts.
Earth's rotation axis is tilted 23.5° relative to its orbital plane — and that tilt stays pointed in the same fixed direction in space all year long, no matter where Earth is in its orbit. That's the key detail people miss: the tilt doesn't wobble to "point at" the Sun. Instead, as Earth travels around its orbit, the fixed tilt means the Northern Hemisphere spends half the year leaning toward the Sun and the other half leaning away from it.
The tilt changes two things at once, and both effects push the same way each season. Sun angle: when the Sun sits higher in the sky, its light lands more directly, concentrating the same energy onto a smaller patch of ground. When it's low, that same light spreads across a larger patch — less energy per square meter. Day length: the higher the Sun's path, the longer it's above the horizon, giving more total hours for that energy to arrive.
Both effects are really about one thing: the Sun's own declination — how far north or south of the celestial equator it sits — which swings between about −23.5° and +23.5° over the year, exactly tracking the tilt. And since declination is exactly what 1.1.2's meridian-altitude relationship uses, you already have the tool to calculate the noon Sun's height on any date.
The Sun's own declination swings between −23.5° and +23.5° across the year. Drag through the seasons and watch the noon Sun's altitude at your latitude, using the exact same relationship from 1.1.2.
An observer at 42°N compares the noon Sun's altitude on the June solstice (Sun's declination ≈ +23.5°) to the December solstice (declination ≈ −23.5°).
Since the tilt leans one hemisphere toward the Sun and the other away from it at the same moment, the two hemispheres are always in opposite seasons. December in Wisconsin is a low sun, short days, and cold — the same December in Australia is a high sun, long days, and the middle of summer. Near the equator, this effect nearly disappears: both hemispheres' tilt contributes about equally there all year, which is why equatorial regions describe their year in terms of wet and dry seasons rather than summer and winter at all.