Glosario - C

Celestial sphere is an imaginary sphere that covers the entire sky and is stationary with respect to the background stars. It is used as a tool for spherical astronomy.

Chromospheric activity index is a parameter indicating the magnetic activity in a star's chromosphere. One measure of this activity is log R′HK, where R′HK is the ratio of the equivalent width of a star's singly-ionized Calcium H and K lines, after correction for photospheric light, to the bolometric flux.[2]

Color index is a numeric value that is used to compare the brightness of a star measured from different frequency bands of the electromagnetic spectrum. Because the energy output of a star varies by frequency as a function of temperature, the color index can be used to indicate the star's temperature.

Comets are relatively small, icy bodies that display extended features when they approach the Sun. The energy from the Sun vaporizes volatiles on a comet's surface, producing a visible coma around the cometary body. Sometimes a comet can produce a long tail radiating away from the Sun.

Commensurability is the property of two objects orbiting the same body whose periods are in a rational proportion. For example, the orbital period of Saturn around the Sun is very nearly 5/2 the orbital period of Jupiter.

Common proper motion is used to indicate two or more stars that share the same motion through space, within the margin of observational error. That is, either they have nearly the same proper motion and radial velocity parameters, which may suggest that they are gravitationally bound or share a common origin,[3] or they are known to be gravitationally bound (in which case their proper motions may be rather different but average out the same over time).

Constellation is a region on the celestial sphere surrounding a grouping of stars. The names of constellations are assigned by tradition and often have an associated folklore based in mythology, while the modern demarcation of their borders are established by the International Astronomical Union in 1930.

The corona is an aura of plasma that surrounds cooler stars such as the Sun. It can be observed during a solar eclipse as a bright glow surrounding the disk. The temperature of the corona is much higher than the stellar surface, and the mechanism that creates this heat remains subject to debate among astronomer.

Critical rotation is the velocity at the equator of a rotating body where the centrifugal force just balances the Newtonian gravity. At this rotation rate, mass can be readily lost from the equator, forming a circumstellar disk.[4]