AstroGlossary - C
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
carbon cycle
A nuclear fusion reaction cycle that occurs in the cores of stars with masses greater than that of our Sun, with temperatures exceeding 16 million degrees. The reaction cycle involves carbon (C), nitrogen (N), oxygen (O), hydrogen (H) and helium (He). Hydrogen is fused into helium with the help of carbon, which acts as a catalyst to the reaction. carbonaceous chondrite
A rare type of meteorite containing water, and complex organic compounds. These may be fossils of our early solar system. Cassegrain focus
A focal point that lies behind the primary mirror of a reflecting telescope. In order to achieve this focus, a reflecting telescope must have a secondary mirror and a hole cut in the center of the primary mirror. Such an optical arrangement compacts the size of the telescope tube and centers the mass close to the primary mirror. Cassini division
A 5000-km gap in Saturn's ring system observable through small telescopes and clear skies. G.D. Cassini discovered this dark gap in Saturn's rings in 1675. celestial equator
The projection of Earth's equator onto the sky. If you were standing on Earth's equator, the celestial equator would extend from eastern horizon, directly over your head (zenith), then to the western horizon. Astronomers use an imaginary projection of Earth's latitude and longitude, called the celestial sphere, to locate planets, stars, star clusters, nebulae and galaxies. See also: equinoxcelestial pole
The projection of Earth's rotation axis poles onto the sky. In the northern hemisphere, the celestial pole is within a degree of Polaris, the North Star. celestial sphere
A coordinate system similar to Earth's latitude and longitude used to locate planets, stars, star clusters, nebulae and galaxies. The celestial sphere is centered on Earth, and it includes the celestial equator, the north and south celestial poles, and lines of right ascension and declination. center of mass
A point that pretends to represent the entire mass of a system of masses or a single rigid mass. Massive bodies in space orbit around a center of mass. Cepheid variable
An unstable star whose brightness changes periodically. In 1912, Henrietta Leavitt discovered what is known as the Period-Luminosity Relationship for Cepheid variables, by which the period of the brightness change is related to the luminosity, and therefore the distance, of the star. An astronomer can record the changing brightness of a Cepheid variable and plot the brightness change over time to create a light curve for the star. The distance to the Cepheid variable is then obtained by measuring the period of the light curve. Ceres
The largest known asteroid, Ceres, is 623 miles (1,003 km) in diameter, and orbits roughly 260 million miles (420 million km) from the Sun. Italian astronomer Giuseppe Piazzi discovered Ceres in 1801. Since it was the first asteroid ever discovered, it also carries the designation "1 Ceres." In 2006, astronomers also classified Ceres as a "dwarf planet." Chandrasekhar limit
The maximum mass of a white dwarf, 1.4 solar masses. Beyond this mass, the star collapses into a neutron star or black hole depending on the mass of the collapsing core. Subrahamanyan Chadrasekhar, at age 19 in 1930, worked out this limiting mass while on a steamship to England. charge-coupled device (CCD)
A light-recording device that revolutionized astronomy. A CCD is a silicon wafer, about the size of a thumbnail, that converts light into an electronic signal which may be manipulated and stored on a computer. In addition, the CCD recording efficiency is high, at about 80 to 95 percent, compared with the low photographic efficiency of film (about one percent). Astronomers mount CCD chips into cameras on a telescope, allowing the astronomer to see 80 to 95 percent farther out into space and time. chromosphere
Literally meaning "sphere of color," the chromosphere is an outer layer of the solar atmosphere sandwiched between the photosphere and the corona. Prominent features of the chromosphere include spicules, and bright hydrogen alpha emission lines, and calcium H and K emission lines. These emission lines suggest a temperature for the chromosphere higher than the photosphere. cluster
A grouping of the same types of astronomical objects. For example, stars in the Milky Way can group together into open clusters or globular clusters. Galaxies also group together into cluster of galaxies, and the clusters of galaxies group together into superclusters of galaxies. comet
An icy, "dirty snowball" (Fred L. Whipple) that orbits the Sun. The majority of comets orbit well beyond Pluto in halos known as the Kuiper Belt and the Oort Cloud that surround the Solar System. Comet size ranges from a few meters to a few kilometers in diameter. Upon close encounters with the Sun, comet ices vaporize, creating a coma, or cloud, around the comet, and a long tail that always points away from the Sun. conjunction
A geometrical arrangement of the Earth, Sun and another planet(s) in a line, with the planet(s) behind the Sun. The complementary arrangement is called opposition, when the planet(s) are behind Earth. Conservation of Energy
The principle that states that energy is neither created nor destroyed, merely exchanged from one form to another. Thus for any closed system (for example, a star or the universe), the total energy is constant, but the amount of energy in any one form may change. constellation
A meaningful pattern of stars visible with the unaided eye, or a region of space seen from Earth that is bounded by borders designated by the International Astronomical Union. Americans know northern hemisphere constellations by the names given them by ancient Babylonians and Greeks. Seafaring explorers named those in the southern hemisphere. Every culture created its own constellations, although most of those in use today came from western sources. continuous spectrum
A smooth-looking spectrum without absorption lines that indicates a thermal source of radiation like a light bulb, star, or other glowing matter. Copernicus, Nicholas
A Polish astronomer who lived from 1473 to 1543. Copernicus is most famous for inventing the Copernican system, which is also known as the heliocentric theory. The Copernican system is a model for our Solar System in which the Earth and all other planets orbit around the Sun and the Sun is the center of the universe. In contrast, scientists before Copernicus ascribed to the Ptolemaic system, also known as the geocentric theory. The Ptolemaic system stated that all the planets, the Moon, and the Sun orbited the Earth, which was the center of the universe. corona
The extended outer atmosphere of the Sun or other star. From Earth, it is visible only during a total solar eclipse. Compared with the photosphere, the corona has a high temperature (1,000,000 degrees) and low density (a million, million times lower). Cosmic Background Radiation (CBR)
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 ray
A high-energy particle that flies through the universe at close to the speed of light. Cosmic rays are mostly bare protons and electrons. Some 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 past, present, and future of the universe, including the structure and evolution of energy, matter, space, and time. crater
A bowl-shaped blemish left on the surface of a planet or moon as the result of an meteoroid impact. Several craters exist on Earth, and thousands litter the surface of the Moon, Mercury, and other solar system bodies.
|
  |
Contact StarDate | About StarDate | Friends of McDonald | Sign up for Sky Tips
