Unit 17
The Earth, the Moon and the Sun.
Day and night, the seasons from the Earth's tilt, the Moon's phases, eclipses, and two tides a day.
Before this unit
- Circular motion and gravity
- Trigonometry Mathematics
The unit, lesson by lesson
Lessons
4 lessons · 24 practice questions · about 2 hours
Day and night
The Earth spins on its axis: why half of it is always lit, how many degrees the Sun moves in an hour, why day and night are equal everywhere at the equinox, how high the noon Sun stands, and what the midnight Sun is.
The seasons
Why summer is hot and winter cold: not the distance from the Sun but the tilt of the axis. The noon Sun's height and the length of the day at latitude $32^\circ$, light spread over more ground, opposite seasons in the south, and what a different tilt would do.
Phases of the Moon
The Sun always lights half the Moon, and through the month we see a different part of that half. First quarter, full moon, how much of the disc is lit each day, and why the Moon rises about $50$ minutes later every day.
Eclipses and tides
Why not every full moon brings a lunar eclipse, when a solar eclipse happens, and how the gravity of the Moon and the Sun lifts the ocean: two high tides a day, spring and neap tides, and why the Sun's tide is small.