Words to Know

• Axis - an imaginary line about which a body rotates.
• Orbit - the curved path of a celestial object or spacecraft around a star, planet, or moon, especially a periodic elliptical revolution.
• Satellite - a celestial body orbiting the earth or another planet or an artificial body placed in orbit around the earth or moon or another planet in order to collect information or for communication.
• Syzygy - the nearly straight-line configuration of three celestial bodies (such as the sun, moon, and earth during a solar or lunar eclipse) in a gravitational system.
• Umbra - the fully shaded inner region of a shadow cast by an opaque object, especially the area on the earth or moon experiencing the total phase of an eclipse.
• Penumbra - the shadow cast by the earth or moon over an area experiencing a partial eclipse.
• Totality - the state or period of an eclipse when light from the eclipsed body is totally obscured.