دیشن ِ لگامش dišan-e legâmeš
*Fr.: indice de freinage*
A parameter indicating the rate at which a → *pulsar*
slows down. Neutron stars are powered by → *rotational energy*
and lose energy by accelerating particle → *wind*s
and by emitting → *electromagnetic radiation*.
The → *rotation frequency*, Ω, thus decreases with time
and this slowdown is usually described by the relation
Ω^{.} = - *kΩn*, where *k* is a positive constant
which depends on the → *moment of inertia*
and the → *magnetic dipole moment*
of the → *neutron star* and *n* is the braking index.
Conventionally, the braking index is derived by differentiation of the above equation,
yielding *n* = ΩΩ^{..} / Ω^{.2}.
In a highly simplified model in which the spin-down torque
arises from dipole radiation at the rotation frequency, one
expects *n* = 3 (Johnston, S., Galloway, D., 1999, arXiv:astro-ph/9905058). → *braking*; → *index*. |

لگامش ِ کشندی legâmeš-e kešandi
*Fr.: freinage des marées*
The physical process that slows the → *Earth's rotation*
rate due to → *tidal friction*.
The → *Earth* rotates faster than the
→ *Moon* orbits the Earth (24 hours compared to 27 days).
The → *friction*
between the ocean and the solid Earth
below drags the → *tidal bulge*
ahead of the line joining the Earth and
the Moon. The → *gravitational attraction*
of the Moon on the bulge provides a braking action on
the Earth and decelerates its
rotation. Tidal braking lengthens the day by 0.002 seconds
every century.
Because the total → *angular momentum* of
the → *Earth-Moon system*
in conserved, the loss in the angular momentum
of the Earth is compensated by the orbital angular momentum of
the Moon. Hence, the Moon moves away from Earth at a rate of about 3 cm per
year. This process must continue until
Earth's → *day* and → *month*
are equal, at which point the Moon will never
seem to move in Earth's sky and Earth is said to be tidally locked to
the Moon (→ *tidal locking*). → *tidal*; → *braking*. |