Celestial objects like Earth move through revolution and rotation. Axial tilt, currently at 23.5 degrees, affects the planet’s condition. Seasons change due to the distribution of light and the varying ratio of day to night. The cause of axial tilt is unknown, but theories include a collision with a celestial body and chaotic dust distribution during the formation of the solar system.
Orbiting celestial objects such as planet Earth move in two ways: revolution and rotation. The former refers to the elliptical motion of a satellite around its parent body, in this case the sun; the latter refers to the circular motion of the body around a central axis as it rotates. The axis of rotation often forms an inclined angle and not perpendicular to the orbital plane. This phenomenon, known as axial tilt or obliquity, has profound effects on the condition of the planet.
The axial tilt of the Earth is currently 23.5 degrees and varies between 22 and 24.5 degrees over a 41,000 year period. Relative to the orbital plane, also known as the ecliptic, the north and south celestial poles move slowly, which causes the planet to almost always tilt in the same direction relative to the solar system as a whole. As the Earth revolves around the sun, the distribution of light from the sun and across the planet varies; the northern and southern hemispheres receive the same amount of light only during the spring and autumn equinoxes. When the Northern Hemisphere is tilted in the direction of the Sun, people in that part of the world experience summer, while the Southern Hemisphere experiences winter. On the opposite side of the orbit, the southern hemisphere tilts towards the sun and experiences the season of summer; the northern hemisphere tilts and has winter
One indicator of seasonal change is the varying ratio of day to night throughout the year, controlled by the Earth’s axial tilt. The side of the Earth facing the sun at any given time experiences the day. When the Northern Hemisphere faces the sun, latitudes north of the equator will have more area in the daytime part of the planet, causing longer days, and the Southern Hemisphere will have shorter days. Moving away from the equator increases this distance; the Arctic Circle located at 66 degrees north marks the point where the entire rotation is on the day or night side of the sun, referred to as the summer and winter solstice, when day or night lasts a full 24 hours. At the poles, day and night last six months.
Scientists have not discovered the cause of the Earth’s axial tilt, but they have put forward some leading theories. The prevailing theory is that a large celestial body collided with the Earth early in its life and caused a tilt in the axis. Another theory is the chaotic distribution of dust at the formation of the solar system, which explains each planet having a different axial tilt.
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