Asteroid (ass-tuh-roid)
A rocky and/or metallic object that is smaller than a planet and orbits the Sun

AU (a u)
The AU or Astronomical Unit is a unit of measurement, like an inch or a foot. It represents the average distance between the Sun and the Earth. It's about 93,000,000 miles (or about 150 million kilometers).

Elliptical orbit (ee-lip-tik-uhl or-bit)
An oval shaped path that forms a closed orbit

Hyperbolic orbit (hye-pur-bah-lik or-bit)
A U-shaped path that forms an open orbit; an object on a hyperbolic orbit has so much energy that it escapes the gravitational pull of the central object and veers off into space.

Mass (mass)
The amount of physical matter an object contains

Matter (mat-ur)
Anything that has mass and takes up space, such as a solid, liquid, or gas

Orbit (or-bit)
The path followed by an object circling a planet, the Sun, etc. The path is defined by the force of gravity.

Perihelion (pear-eh-heel-eon)
The point in its orbit where a planet or other space object is closest to the Sun. (Apihelion is the point in its orbit where a planet or other space object is farthest from the Sun.)

Solar radius (soh-lur ray-dee-uhss)
A unit of measurement, like an inch or a foot. At half the diameter of the Sun, it's smaller than an AU.

Velocity (vuh-loss-uh-tee)
Speed and direction