DICTIONARY OF GEOPHYSICS, ASTROPHYSICS, and ASTRONOMY

and its density 2.8 g cm −3 . Its geometric albedo
is not well determined, and it orbits Jupiter (retrograde)
once every 692 Earth days.
Carnot cycle An ideal thermodynamic reversible
cycle over a substance which consists
of the following four processes: 1. isothermal
expansion, in which the substance does work
and there is inflow of heat Q2 at a constant temperature
T2; 2. adiabatic expansion, in which
the substance is thermally insulated and does
work, there is no heat flow, and the temperature
of the substance decreases; 3. isothermal compression,
work is done on the system and there
is outflow of heat Q1 at a constant temperature
T1; 4. adiabatic compression, the substance is
thermally insulated, and work is done on the
substance, there is no heat flow, temperature of
the substance increases, and at the end of this
process the substance returns to its initial state.
By applying the second law of thermodynamics
to the Carnot cycle, one shows that the ratio
of heat inflow and heat outflow Q2/Q1 for a
substance undergoing a Carnot cycle depends
only on the temperatures T2 and T1 and is independent
of the substance. Applying the Carnot
cycle to an ideal gas, one further shows that the
ratio of heat outflow and heat inflow is equal
to the ratio of the corresponding temperatures,
i.e., Q1/Q2 = T1/T2. One can then represent
an arbitrary reversible cyclic process by a series
of Carnot cycles and show that
rev dQ/T = 0
for any reversible process. This in turn leads
to the definition (up to an arbitrary constant) of
entropy S =
rev
dQ/T as a thermodynamic
function of state. Named after Nicolas Léonard
Sadi Carnot (1796–1832).
Carnot efficiency The ratio between the
work done and the amount of heat introduced
into a system going through a Carnot cycle. The
Carnot efficiency is equal to the difference between
the two temperatures of the isothermal
steps of the cycle divided by the higher of the
two temperatures.
Carnot engine An ideal heat engine whose
working substance goes through the Carnot cycle.
A heat engine receives heat at a given temperature,
does work, and gives out heat at a lower
temperature. The efficiency of a Carnot engine
© 2001 by CRC Press LLC
Carter–Peter model
or Carnot efficiency is the maximum efficiency
possible for a heat engine working between two
given temperatures.
Carrington longitude A fixed meridian on
the sun as measured from a specified standard
meridian. Measured from east to west (0 ◦ to
360 ◦ ) along the sun’s equator. Carrington longitude
rotates with the sun and is a particularly
useful coordinate when studying long-lived features
on the sun. When combined with a Carrington
rotation number, the Carrington longitude
is commonly used as an alternative to specifying
a time.
Carrington rotation The period of time covering
360 ◦ of Carrington longitude. Used to
provide a temporal reference frame where the
time unit is a solar rotation period. For example,
Carrington rotation 1917 corresponds to the
time period 9 December 1996 to 5 January 1997,
while Carrington rotation 1642 relates to the rotation
between 28 May 1976 and 23 June 1976.
Carter–Peter model The dynamics of a superconducting
cosmic string is macroscopically
describable by means of the duality formalism.
This formalism only requires the knowledge of a
Lagrangian function L depending on a state parameter
w, the latter being interpretable as the
squared gradient of a phase φ, namely
w = κ0γ ab ∂aφ∂bφ ,
with κ0 a normalization coefficient, γ ab the inverse
of the induced metric on the string surface,
and the superscripts a, b representing coordinates
on the worldsheet. In the Carter–Peter
(1995) model for describing a conducting cosmic
string of the Witten kind, the Lagrangian
function involves two separate mass scales, m
and m⋆ say, respectively describing the energy
scale of cosmic string formation and that of current
condensation; it takes the form
L =−m 2 − m2⋆ 2 ln
1 + w
m2
.
⋆
This model implies the existence of a first order
pole in the current, as is the case in realistic conducting
string models taking into account the
microscopic field structure. The figure shows