Slow, circular movement at the top of Earth's axis

• precession
• barycenter
• revolution

A wobble back and forth

• Rotation
• Nutation
• Revolution

Earth revolves around the sun

• Precession
• Rotation
• Revolution

Spinning on an axis

• Rotation
• Nutation
• Solstice

The angle the sun's rays strike the earth's surface

• Fusion
• Insolation
• Angle of Insolation

The center of mass of an object

• Angle of Insolation
• Barycenter
• Equinox

The time and date of the year when day and night are equal length. 

• Fusion
• Solstice
• Equinox

2 times a year when the sun reaches the highest or lowest point; shortest and longest day. 

• Beltane
• Solstice
• Equinox

Exposure to the sun's rays

• Fusion
• Insolation
• Fission

The process of joining two or more things together

• Fision
• Fusion
• Isotope