A celestial body that travels around the sun, usually in a highly eccentric orbit: thought to consist of a solid central mass part of which vaporizes on approaching the sun to form a gaseous luminous coma and a long tail of dust and gas.

Any of the 88 groups of stars as seen from the earth and the solar system, many of which were named after characters from classical Greek and Roman mythology as well as various common animals and objects.

The branch of astronomy that deals with the origin, development, and structure of the universe.

A measure of the amount of disorder in a system. A quantity specifying the amount of disorder or randomness in a system bearing energy or information.

A large collection of stars held together by mutual gravitation and is separate from similar systems by large regions of space.

(1564-1642) Italian astronomer and mathematician who was the first to use a telescope to study the stars; perfected the refracting telescope that enabled him to make many significant discoveries.

Edwin Powell Hubble (1889–1953) was a US astronomer who during the period of 1924–26, was the first to detect stars of galaxies outside of our own Milky Way galaxy. Also, in 1929 Hubble discovered that the velocities of galaxies increase with distance.

An orbiting astronomical space observatory put into space  in 1990, designed to observe extremely distant stars, galaxies, nebula from its orbit 370 mi. (592 km) above the earth’s atmosphere.

The distance that light travels in a vacuum in one year, approximately 9.46 trillion kilometers (5.88 trillion miles).

A diffuse cloud of interstellar dust or gas or both, visible as bright patches or areas of darkness depending on the way the mass absorbs or reflects incident light or emits its own light.

(1642-1727) English mathematician and physicist; known for creating calculus and for his law of gravitation and his three laws of motion.

Also called: the Pole Star or Polaris in the constellation Ursa Minor and is the brightest star of the Little Dipper which is a cluster of seven stars and at the end of the dipper’s handle is Polaris.

An open star cluster in the constellation Taurus, made up of several hundred stars of which six are visible to the naked eye. According to Greek mythology the seven daughters of Atlas (Maia, Electra, Celaeno, Taygeta, Merope, Alcyone, and Sterope), were metamorphosed into stars.

See North Star (Polaris).

A celestial body that produces light and other radiant energy. It also consists of a mass of gas held together by its own gravity in which the energy generated by nuclear reactions in the interior is balanced by the outflow of energy to the surface, and the inward-directed gravitational forces are balanced by the outward-directed gas and radiation pressures.

The sun along with the eight planets, moons and all other celestial bodies that orbit the sun.

It is a powerful and extremely bright stellar eruption.  The original object, called the progenitor, either collapses to a neutron star black hole, or is completely destroyed. The peak optical brightness of a supernova can be comparable to that of an entire galaxy.

The aggregate of spacetime, matter, and energy, including the solar system, all stars and galaxies, and all the workings of intergalactic space, regarded as a whole.