The idea
Seasons, phases, eclipses, and tides all follow from geometry — the relative positions of Sun, Earth, and Moon.
Seasons come from tilt, not distance
Earth’s axis is tilted . In June the northern hemisphere leans toward the Sun: light arrives more directly and days are longer.
The number one misconception in astronomy
Earth is actually closest to the Sun in early January. If distance caused seasons, both hemispheres would have summer at the same time. They do not. Tilt is the answer.
Phases of the Moon
| Phase | Moon’s position | What you see |
|---|---|---|
| New | Between Earth and Sun | Nothing — lit side faces away |
| First quarter | 90° along the orbit | Right half lit |
| Full | Opposite the Sun | Fully lit |
| Third quarter | 270° along | Left half lit |
The Moon is always half lit. What changes is how much of the lit half we can see from here.
Eclipses
graph LR SUN["Sun"] --> MOON["Moon"] --> EARTH["Earth"] SUN --> EARTH2["Earth"] --> MOON2["Moon"]
- Solar eclipse — Moon between Sun and Earth (only possible at new moon)
- Lunar eclipse — Earth between Sun and Moon (only at full moon)
So why not one of each every month?
The Moon’s orbit is tilted about from Earth’s. Most months the shadow misses. Eclipses need the alignment to be nearly perfect — which is why they are worth travelling to see.
Curriculum connection
E2.6
conduct investigations to explain the causes of various astronomical phenomena that can be observed from Earth
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E2.2
explain how the Sun’s energy causes natural phenomena on Earth, and how these phenomena contribute to renewable energy production
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