The following glossary includes terms that are used in Student Text, Tracing the Origins of our Universe. You will probably want to study the terms and their definitions before you read the student text.

Epoch
An epoch is a period of time characterized by a distinctive development. In this student text, the history of the universe is divided into eight epochs.

Gluons
Gluons are massless carriers of the strong nuclear force, the force that acts between quarks to form protons and neutrons.

Interstellar
Interstellar refers to space between stars.

Kelvin temperature scale
The Kelvin is the International System of Units temperature unit. It was named for Lord Kelvin, a British physicist. The size of a degree on the Kelvin scale is the same as that on the Celsius scale. The zero point on the Kelvin scale is called absolute zero. It is the same temperature as negative two hundred seventy three on the Celsius scale.

To compare the three temperature scales, the freezing point of water is thirty-two degrees on the Fahrenheit scale. On the Celsius scale it is zero degrees and it is two hundred seventy three on the Kelvin scale.

Plasma
Plasma is sometimes called the fourth state of matter. It is gaseous and contains electrically-charged particles, like free electrons and positively- and negatively-charged ions. Plasma contains equal numbers of positive and negative charges.

Quarks
Quarks are fundamental particles that form protons and neutrons.

Solar wind
Solar wind is the hot, fast-moving flow of solar material that carries plasma of mostly high-energy protons, helium nuclei and electrons from the sun into space.

Standard cosmological model
The standard cosmological model is a scientific model that explains what cosmologists have observed about today’s universe and how the universe was formed. Cosmologists applied mathematics and fundamental physical laws to their observations to describe eight major epochs of cosmic evolution.

Strong Nuclear Force
The strong nuclear force is force holds that holds protons and neutrons very tightly together to form an atom’s nucleus. It is also called “chromoelectric” force, because the gluons that carry it have an assigned characteristic called “color.”

Supernova
A supernova is a star that explodes following the exhaustion of its nuclear fuel, becoming for a few days up to one hundred million times brighter than the sun.