The Earth, sun and moon as one system of cycles: spinning and orbiting, seasons from a tilted axis, the moon's phases, eclipses, and tides. Concept tutorials with a live model seen from above and from the side.
Rotation, revolution and the tilted axis; seasons (AC9S7U03).
The Earth rotates (spins on its axis) once a day, causing day and night, and revolves (goes round the sun) once a year. Its axis is tilted and always points the same way in space.
Seasons are caused by the Earth's tilted axis, not its distance from the sun. Leaning towards the sun gives a higher noon sun (concentrated light) and longer days: summer. The two hemispheres have opposite seasons.
Phases, eclipses and tides (AC9S7U03).
The sun always lights half of the moon. As the moon goes round the Earth (29.5 days from new moon to new moon), we see more or less of that lit half: the phases. They are not caused by Earth's shadow.
A solar eclipse happens at new moon when the moon's shadow falls on Earth; a lunar eclipse at full moon when the moon passes through Earth's shadow. The moon's orbit is tilted about 5°, so most months the shadows miss: eclipses come in seasons about six months apart.
The moon's gravity pulls the oceans into two bulges, one facing the moon and one on the far side; the Earth spins through both, so most coasts get two high tides a day. Spring tides (biggest range) come at new and full moon, when the sun and moon pull in line; neap tides at the quarters.
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