Either of two times of the year, the north pole (~ June 21) or the south pole (~ December 21) is most directed toward the Sun.

Either of fall or spring times of the year during a planet’s orbit when the north and south poles are equidistant from the Sun, causing day and night to be equal in length

The curved path of one object, such as a planet or moon, around a central object, such as a star or planet

A force of attraction between two objects.

A physical feature of a planet’s surface, such as a mountain, plain, or valley

Layers of lava alternate with layers of tephra; large and wide

Erupting lava explodes, breaks apart in the air, then settles around the volcano’s central vent, forming steep sides

Flowing lava slowly builds up wide, gently-sloped sides, close to the ground

A deep gorge formed on the ocean floor when an oceanic plate moves beneath a continental plate.

A measure of the damage done by an earthquake; determined by the earthquake’s effect on people, structures, and the natural environment.

A measure of the total amount of energy released at the focus of an earthquake.