Permittivity of free space or vacuum permittivity refers to the interaction between electricity and force as well as the effects of space on electrons. In a purely theoretical sense, permittivity of free space refers to a vacuum’s ability to maintain the bonding effects of individual electrons.

The Fine Structure Constant is a constant in theoretical physics that determines the strength of the interaction between two opposing electromagnetic waves. The Fine Structure Constant is used for a wide variety of purposes, but is entirely hypothetical and does not depend on any real units of physics.

Apogee is a term used to describe the point at which a satellite or object in orbit is at its furthest distance away from the Earth. When an object is at its apogee, it travels much slower than at any other point in its orbit because the Earth has less of a pull on it.

Perigee is a term used to describe the closest point at which an object orbits the Earth or another object in space.

A geostationary orbit is when a satellite orbits the Earth at the same speed as the Earth’s rotation at a fixed location. The satellite remains in the same position while it provides coverage of the same area on the Earth’s surface.

A geosynchronous orbit is when a satellite or other device’s orbit matches the Earth’s rotation so that the satellite travels around the Earth in a straight line and stays at the same point in the sky relative to the Earth.

Blackbody radiation refers to the electromagnetic radiation that a blackbody material expels. Blackbody materials are substances that absorb all electromagnetic radiation that comes in contact with it, including light and heat. While a perfect blackbody material does not exist in nature, substances such as ash, soot, and granite come close.

Ion propulsion refers to a method of space travel in which accelerating ions, rather than traditional chemical rockets, speed up a spacecraft. While ion propulsion produces very little thrust in comparison to chemical propulsion, it produces consistent acceleration that allows the spacecraft to eventually travel faster than a chemical rocket would.

Quasars are a phenomena that, to this day, continue to baffle and confuse astronomers. There are different theories. One is that a quasar is formed from a super, massive black hole. Another theory is that a quasar is actually a baby galaxy and is at the earliest stages of development.

Stars form within clouds of dust that are scattered around the galaxies of our Universe. In essence, a star is dust that is pulled toward a central point of gravity and, when this happens, begins to heat up. The formation of a star results in something like our own Sun which took 50 million years to turn into what it is today.