angle: The space (usually measured in degrees) between two intersecting lines or surfaces at or close to the point where they meet.
astronomer: A scientist who works in the field of research that deals with celestial objects, space and the physical universe.
constant: Continuous or uninterrupted. (in mathematics) A number that is known and unchanging, usually based on some mathematical definition. For example, π (pi) is a constant equal to 3.14. . . and defined as the circumference of a circle divided by its diameter.
crater: A large, bowl-shaped cavity in the ground or on the surface of a planet or the moon. They are typically caused by an explosion or the impact of a meteorite or other celestial body. Such an impact is sometimes referred to as a cratering event.
diameter: The length of a straight line that runs through the center of a circle or spherical object, starting at the edge on one side and ending at the edge on the far side.
digit: (in math) An individual numeral (from 0 to 9) used to represent a number or some part of a number.
Infinity: An abstract concept in which something has no end.
moon: The natural satellite of any planet.
orbit: The curved path of a celestial object or spacecraft around a galaxy, star, planet or moon. One complete circuit around a celestial body.
pi: (in mathematics) Usually written using the Greek letter π. It is a constant equal to 3.14. . . and defined as the circumference of a circle divided by its diameter.
radius: A straight line from the center to the circumference of a circle or sphere.
ratio: The relationship between two numbers or amounts. When written out, the numbers usually are separated by a colon, such as a 50:50. That would mean that for every 50 units of one thing (on the left) there would also be 50 units of another thing (represented by the number on the right).
star: The basic building block from which galaxies are made. Stars develop when gravity compacts clouds of gas. When they become hot enough, stars will emit light and sometimes other forms of electromagnetic radiation. The sun is our closest star.
unit: (in measurements) A unit of measurement is a standard way of expressing a physical quantity. Units of measure provide context for what numerical values represent and so convey the magnitude of physical properties. Examples include inches, kilograms, ohms, gauss, decibels, kelvins and nanoseconds.