Over long periods of geological time, the angle of Earth’s obliquity cycles between 21.1 and 24.5 degrees. The extra weight would cause the ball to tilt when spun. An analogy for obliquity is imagining what would happen if you were to spin a ball with a piece of bubble gum stuck near the top. Large amounts of land mass and ice sheets in the Northern Hemisphere make Earth top-heavy.
The tilt in Earth’s axis is strongly influenced by the way mass is distributed over the planet. Autumn in New Jersey’s Pinelands, by our friend Jeanette York. Seasons in the Southern Hemisphere occur at opposite times of the year from those in the Northern Hemisphere. When the Northern Hemisphere is oriented away from the sun, the sun’s rays are less direct, and that part of Earth cools. The sun’s rays are striking that part of Earth at a more direct angle. When the Northern Hemisphere is oriented toward the sun, that region of Earth warms because of the corresponding increase in solar radiation. The same is true of the Southern Hemisphere. In other words, the Northern Hemisphere is oriented toward the sun for half of the year and away from the sun for the other half.
But the orientation of Earth’s tilt with respect to the sun – our source of light and warmth – does change as we orbit the sun. At this time, that direction is more or less toward the star we call Polaris, the North Star. In other words, Earth’s northern axis is always pointing the same direction in space. Over the course of a year, the angle of tilt does not vary. The tilt in the axis of the Earth is called its obliquity by scientists. Instead, Earth has seasons because our planet’s axis of rotation is tilted at an angle of 23.5 degrees relative to our orbital plane, that is, the plane of Earth’s orbit around the sun. That’s logical, but not the case for Earth.
Some assume our planet’s changing distance from the sun causes the change in the seasons. Today’s equinox signals the change of season, from summer to fall in the Northern Hemisphere and in the Southern Hemisphere from winter to spring.