Astro Glossary

Copernicus, Nicolaus

A Polish astronomer who lived from 1473 to 1543. Copernicus is most famous for devising the Copernican system, which is also known as the heliocentric theory. The Copernican system is a model for our solar system in which Earth and all the other planets orbit the Sun and the Sun is the center of the universe. In contrast, most scientists before Copernicus subscribed to the Ptolemaic system, also known as the geocentric theory, which stated that all the planets, the Moon, and the Sun orbited Earth, which was the center of the universe.

Corona

The corona is the hot extended atmosphere of a star. In the case of the Sun, it extends millions of miles (km) into space, and is heated to more than a million degrees, compared to about 10,000 degrees Fahrenheit (5,800 Centigrade) for the surface. It is heated by magnetic activity at or near the Sun's surface, although astronomers are still trying to determine the exact mechanism. Although it is hot, the corona is so thin and faint that it's visible from Earth's surface only during a total lunar eclipse. Astronomers study it with special instruments that block out the disk of the Sun, or with space telescopes. Other stars generate their own coronas.

Corona Australis, the Southern Crown

Corona Borealis, the Northern Crown

Cosmic Background Radiation

An electromagnetic radiation field at a black body temperature of 2.7 Kelvin that fills the entire universe uniformly to 0.00001 Kelvin. Also known as the Cosmic Microwave Background (CMB), it is thought to be the residual glow from the very hot early universe that followed the Big Bang.

Cosmic Jets

Streams of electrically particles shooting into space from the poles of some objects, such as newborn stars and black holes. A jet is powered by a strong magnetic field that captures particles from the inner edge of a rotating disks that encircles the central star or black hole. The magnetic field shoots the particles into space at close to lightspeed. The particles in a jet produce radio waves and other types of energy that can be detected by telescopes on Earth or in space. The jets around supermassive black holes can stretch across tens of thousands of light-years.

Cosmic Rays

High-energy particles that fly through the universe at close to the speed of light. Cosmic rays are mostly bare protons and electrons. Some probably are blasted into space from exploding stars, while others may come from the disks of material that encircle the supermassive black holes in the centers of galaxies.

Cosmology

The study of the birth, evolution, and fate of the universe.

Crab Nebula, M1

A cloud of glowing gas that is the remnant of a supergiant star that was seen to explode in 1054. It’s called the crab because its tendrils of gas, which span several light-years, resemble a crab. It is one of the most famous objects in the galaxy.

Crux, the Southern Cross