User:Sandraisrael/sandbox

Orbital Seasons

The seasons reversed for the southern hemisphere. The solstices mark the two dates during the year on which the Earth's position in its orbit is such that its axis of rotation is most tilted toward or away from the Sun. The seasons are caused by the 23.4° angular offset between the Earth's axis of rotation and a perpendicular to the Earth's orbital plane with the Sun. The Earth's rotational axis stays fixed in space. As a result, when the Earth is at a certain place in its orbit, the northern hemisphere is tilted toward the Sun and experiences summer. When the Earth is on the opposite side of the Sun six months later, the northern hemisphere is tilted away from the Sun and experiences winter. The seasons are reversed for the southern hemisphere.

Long-Term Astronomical Cycles

Most of the difference in the average lengths of the two kinds of year is due to the slight change in the direction of the Earth's axis of rotation in space from one year to another. We usually think of the Earth's axis of rotation as being fixed in direction. After all, it always seems to point toward Polaris, but the direction is not quite constant. The axis does move at a rate of a little more than a half-degree per century. So Polaris has not always been, and will not always be, the pole star.