DICTIONARY OF GEOPHYSICS, ASTROPHYSICS, and ASTRONOMY

cyclongenesis
air masses along fronts. According to the structure
of temperature and pressure, a cyclone can
be classified as a barotropic cyclone (cold cyclone
and warm cyclone), a baroclinic cyclone,
or a neutral cyclone. Based on the distribution
of geography, it can be classified as an extratropical
cyclone, subtropic cyclone, or tropical
cyclone. Since its lower level convergence can
cause ascending air motion, cyclones are often
accompanied by clouds and rain.
cyclongenesis A development of synopticscale
weather disturbances.
cyclotron damping and instability In a collisionless
plasma, damping or instability associated
with then=±1 resonance, of importance
in space physics and astrophysics as a mechanism
of pitch-angle scattering of charged particles.
See resonant damping and instability.
cyclotron frequency See Larmor frequency.
cyclotron radius See Larmor radius.
Cygnus A Nearby (z = .056, about 200Mpc
distant) active galaxy (3C 405) at RA19 h 59.4 m ,
dec+40 ◦ 43 ′ which is a strong radio source, with
radio jets that extend for about 50kpc in either
direction. The closest and second strongest radio
galaxy. Recently detected to have a small
quasar-like core.
© 2001 by CRC Press LLC
Cygnus Loop Supernova remnant at RA20 h
49 m 00 s dec+30 ◦ 30 ′ , 230 ′ × 160 ′ in extent. In
the optical, a large filamentary loop, also strong
in radio, visible in X-ray. Age of remnant is
estimated at 20,000 years.
Cygnus X1 (Cyg-X1) A binary system at
RA 19 h 56 m 22 s .0, dec +35 ◦ 03 ′ 36 ′′ , at distance
2.5 kpc, consisting of the O9.7 supergiant HDE
226868 (Gies and Bolton 1986) and a compact
object with an orbital period of 5.6 days. The
mass of the unseen companion is significantly
larger than 5M⊙, probably as large as 12M⊙.
Cygnus X1 is the second brightest X-ray source
in the sky, with X-ray emission exhibiting strong
variability at time scales from milliseconds to
years. It also radiates in γ -radiation. Because
no theoretical models exist of compact degenerate
(neutron) stars of mass exceeding 5M⊙,
the system is taken as the prototype of a black
hole binary. In this model, the compact object
of mass ≈ 12M⊙ is the putative black hole, accreting
mass from the hot supergiant companion
star which has overflowed its Roche lobe
through an accretion disk which thermally emits
X-radiation. Cygnus X1 is also a radio source,
with radio flux correlated to X-ray output. Also
called 4U 1956+35.
cynthion Of or pertaining to the moon.
Cytherean Venusian, referring to the planet
Venus.