What causes the change in daylight hours?
The tilt of the Earth's axis (23.5°) and, to a much lesser extent, the distance from the Sun causes a change in daylight hours.
The length of the days is based on the relation between the earths tilt and the effect that it has on the areas on earth that are most exposed to the sun, i.e. during our summer the northern hemisphere is more significantly in the circle of light cast on the planed by the sun. These pics help to show how one hemisphere is more in the sunlit area then another during the seasons.
When is the earth closest to the Sun?
January @ 0.98329134 AU- here is a graph showing the distance (kilometers) of the earth from the sun over time (days).
Do the seasons and/or tilt depend on distance from the Sun?
Seasons have only to do with the tilt of the planet, and not with the distance from the sun (one hemisphere has summer while the other has winter). Tilt is not related to distance from the sun; all of the planets in our solar system have seasons. Tilt of the planets in our solar system are varied.
Why don’t the planets crash into the Sun?
Planets don't crash into the sun because the forces that are acting on it are, primarily, the gravity between the planet and the sun, and the tangential velocity, which is very similar to centripetal forces. Say you're riding the 'Spizzler' you feel as though you're being pushed back into your seat, however what is actually happening is that your velocity in tangential from every point in the circle you're moving in, so the force you feel is the seat overcoming your tangential velocity to move you in a circle. Also centrifugal force is a giant lie!!
