Why is earth's axis tilted?

Question

Why is the axis of earth tilted? It can't possibly be that the Northern hemisphere is larger causing it to be pulled toward the sun, because then it would always be summer in the N hemisphere and winter in the S hemisphere. If the cause for the tilt is because a large space object collided with earth offsetting the axis, then wouldn't earth keep moving in the direction of the collision? Any insite would be appreciated.

Answer 1

The simple answer: Because it is.

There's a nice theory that explains why the rotation axis of a big gas giant is more or less coaligned with its orbital angular momentum vector. Those big gas giants form somewhat like a snowball rolling downhill becomes bigger and bigger and bigger. This doesn't apply to rocky planets, let alone lesser gas giants and ice giants. Saturn's rotation axis is inclined by 27°, Uranus by 98°, Neptune by 30°. It's a bit random.

With regard to the rocky planets, whatever rotation Mercury had in the distant past is long lost. Tidal interactions with the Sun will necessarily have locked Mercury into a resonance between rotation and orbital rotations. That the resonance is 3:2 rather than 1:1 is a result of the largish eccentricity of Mercury's orbit.

Mars is not tidally locked, but it's obliquity is notoriously chaotic. A number of past and future recreations of Mars' rotation show chaotic behavior. Whatever rotation Mars had when it formed has long been lost thanks to that chaos. The obliquity of Mars has gone through huge changes over the last few billion years, occasionally changing rapidly, occasionally remaining stable. That's the nature of chaos.

Venus also isn't tidally locked per se, but essentially it is. The rotation of Venus is rather bizarre. The solid part of the planet rotates retrograde at a very slow rate. On the other hand, the upper parts of Venus' thick atmosphere rotate prograde. The combined rotation represents one of the four final states in which Venus as a whole can rotate (multiple articles by Laskar, and by others). Venys is in its final rotational state.

The Earth is a marked exception amongst the rocky planets. The key to that marked exception is our exceptionally massive moon. The Earth's moon acts to stabilize the Earth's rotation. Whatever obliquity the proto-Earth had prior to the giant impact is long lost. On the other hand, the obliquity after that giant impact has remained fairly constant thanks to that stabilizing influence.

Answer 2

Earth's Spin

Earth rotating clockwise is the result of a chain reaction that started when Earth's star formed as the result gas clouds collapsing. During the collapse of the gas, one direction was shorter and a disc formed. Due to the law of conservation of angular momentum, the disc gained an overall spin, which was passed to all the objects of notable mass within its solar system; these objects are commonly known as planets. As a result, all plants within a given solar system have the same spin as the star in their solar system to start.

Might be worth noting that all rotating bodies that rotate clockwise when viewed from the southern hemisphere rotate and counter-clockwise when viewed from the northern hemisphere. Also, since the Sun is not solid on the surface, it does not rotate as a solid body; meaning it rotates faster at its equator and slower at its poles.

Earth's Axis

As for the reasoning behind, the axis of the rotation, as pointed out in other answers, this is the result of Earth's past impacts with objects of enough mass to produce the shift from a zero offset from the stars axis, to the current axis of the rotation. Future impacts would be able to change the rotation.

Current Axis of the Planets in Earth's solar system