DICTIONARY OF GEOPHYSICS, ASTROPHYSICS, and ASTRONOMY

scattering albedo
perpendicular shock, the momentum perpendicular
to both shock and magnetic field after the
interaction between particle and shock is
p2⊥
p1⊥
= Bd
=rB .
Bu
The normal component of the momentum remains
unchanged. Thus, the change in momentum
(and energy) is determined by the magnetic
compression rB, the ratio between the downstream
and upstream magnetic field strength.
For oblique shocks, the gain in momentum is
smaller than in the above equation. A crude approximation
for the energy gain here is E ∼
ouu/θBn with uu being the upstream plasma
speed and θBn as angle between magnetic field
direction and shock normal. On average, the energy
gain during one interaction between particle
and shock is a factor between 1.5 and 5. Additional
energy gain, for instance to accelerate
MeV particles out of the solar wind plasma, requires
repeated interactions between shock and
particle and therefore sufficiently strong scattering
in the upstream medium to reflect the particle
back to the shock front. See diffusive shock
acceleration.
scattering albedo See albedo of single scattering.
scattering angle The angle between the directions
before and after scattering.
scattering coefficient The limit of the ratio
of the incident power at a prescribed wavelength
that is scattered within a small volume to the distance
of photon travel as that distance becomes
vanishingly small [m −1 ].
scattering cross-section When a beam of
radiation or particles with a uniform flux f of
energy or particles (e.g.,N particles per second
per square centimeter) is incident on a scatterer,
the amount scattered per unit time is: f ′ =fA,
which defines the scattering cross-section A.
Cross-section has units of area.
scattering efficiency factor The ratio of
the scattering cross-section to the geometrical
cross-section of the particle.
© 2001 by CRC Press LLC
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Schmidtcamera Typeofreflectingtelescope
invented by Bernhard Schmidt, which uses a
thin correcting lens (“correcting plate”) at the
front of the telescope, which corrects the spherical
aberration arising from the spherical primary
mirror. This design leads to a large field of view
(degrees across). Detection is usually made at
prime focus in a Schmidt camera. See prime
focus.
Schwarzschild black hole In general relativity,
a spherical, non-spinning black hole. See
black hole, Schwarzschild metric.
Schwarzschild metric (Schwarzschild solution)
The unique metric of empty spacetime
outside an uncharged spherical source (see
Birkhoff theorem), found by K. Schwarzschild
in 1915.
In spherical coordinates (t,r,θ,φ), the line
element takes the form (c is the speed of light
and G is Newton’s constant)
ds 2 =−
1 −
+ 1 −
2 GM
c 2 r
2 GM
c 2 r
dt 2
−1
dr 2
2
+ r dθ 2 + sin 2 θdφ 2
where M is the mass parameter of the source.
The radial coordinate r ranges from r0 (corresponding
to the surface of the source) to +∞.
Further, for r0 = constant to be a sensible (that
is time-like) trajectory, one needs r0 >RG (region
I), where RG ≡ 2 GM/c 2 is the so-called
gravitational radius, or Schwarzschild radius.
If one assumes that the space-time is vacuum
everywhere, the above form is valid for any values
of r from 0 to +∞ and one encounters a
singularity at r = 0, a real singularity where the
curvature tensor diverges. The value RG instead
is a coordinate singularity (the curvature tensor
is smooth and finite at r = RG). The properties
of the Schwarzschild solution led to the
introduction of the notion of a black hole. The
surface r = RG,t =+∞is the future event
horizon which screens the Schwarzschild black
hole of mass M. The area of the horizon is
A = 16πG2 M 2
c 4
,