Obliquity

Obliquity refers to the angle between an object's rotational axis and its orbital axis, or, equivalently, the angle between its equatorial plane and orbital plane. It differs from inclination. For a planet, obliquity can change the amount of sunlight reaching different parts of the planet's surface at different times of the year, thus having a direct impact on climate in many cases.

Overview

Obliquity is the reason why we have seasons. As the Earth orbits the sun, its tilted axis always points in the same direction. So, over the course of a year, the North Pole tilts towards the sun for half of the year and away for the other half. The tilt increases the amount of daylight received in a given location during the summer and decreases it during the winter.

Obliquity of the Ecliptic

The obliquity of the ecliptic is the tilt of the Earth's axis relative to its orbit around the sun. It is currently about 23.44 degrees and is decreasing. The obliquity of the ecliptic has a significant effect on the climate. When the obliquity increases, the summers and winters in high latitude regions can become more intense, while the tropics become cooler.

Axial Tilt

The axial tilt, also known as obliquity, varies between 22.1 and 24.5 degrees over a cycle of about 41,000 years. The Earth's current axial tilt is 23.44 degrees. This tilt is in the decreasing phase of its cycle, and will reach its minimum value around the year 10,000 AD.

Obliquity in the Solar System

All the planets in the Solar System have obliquities that vary from 0 (for a planet with its axis perpendicular to the plane of its orbit) to 180 degrees (for a planet with its axis parallel to the plane of its orbit and rotating in the opposite direction to its orbit). The Earth's obliquity is currently 23.44 degrees.

See Also

• Axial tilt
• Ecliptic
• Orbit
• Season
• Solar System

References

Obliquity Resources
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