Here's why:
* Kepler's Laws of Planetary Motion: The Earth's orbit around the Sun is not a perfect circle, but rather an ellipse. Kepler's Second Law states that a planet sweeps out equal areas in equal times. This means that when the Earth is closer to the Sun, it needs to move faster to cover the same area in the same amount of time.
* Conservation of Angular Momentum: Another way to think about it is through the principle of conservation of angular momentum. Angular momentum is a measure of how much an object is rotating or revolving. As the Earth gets closer to the Sun, its distance from the axis of rotation (the Sun) decreases. To maintain a constant angular momentum, the Earth must increase its orbital velocity.
Therefore, the Earth's orbital velocity is at its maximum at perihelion, around early January, and at its minimum at aphelion, around early July.
