A plot displaying the amplitude of
→ cosmic microwave background anisotropy
as a function of angular size or → multipole index.
Same as → angular fluctuation spectrum.
The plot, based the on WMAP and other data, shows a plateau at large angular or length
scales (→ Sachs-Wolfe plateau),
then a series of peaks at progressively smaller scales.
These features arise from the gravity-driven
acoustic oscillations of the coupled photon-baryon fluid in the early
Universe (→ baryon acoustic oscillation).
In particular, a strong peak is seen
on an angular scale (at l ~220), corresponding to the physical
length of the → sound horizon at the
→ recombination era.
It depends on the curvature of space. If space is
positively curved, then this sound horizon scale will appear larger on
the sky than in a flat Universe (the first peak will move to the
left). The second peak (l ~ 550), which is the first harmonic of the
main peak, relates to the baryon/photon ratio. The third peak can be
used to help constrain the total matter density.

The angular velocity of a point in a circular orbit around a central mass. It
is given by:
Ω_{K} = (GM/r^{3})^{1/2},
where G is the → gravitational constant, M is
the mass of the gravitating object, and
r is the radius of the orbit of the point around the object.

1) Mechanics: The → angular momentum
associated with the motion of a particle about an origin, equal to the cross product
of the position vector (r) with the linear momentum (p = mv):
L = r x p. Although r and p are constantly changing
direction, L is a constant in the absence of any external force on the system.
Also known as orbital momentum.
2) Quantum mechanics: The → angular momentum
operator associated with the motion of a particle about an origin, equal to
the cross product of the position vector with the linear momentum, as opposed to the
→ spin angular momentum.
In quantum mechanics the orbital angular momentum is quantized. Its magnitude
is confined to discrete values given by the expression:
ħ &radic l(l + 1), where l is the orbital angular momentum quantum
number, or azimuthal quantum number, and is limited to positive integral values
(l = 0, 1, 2, ...). Moreover, the orientation of the direction of rotation is
quantized, as determined by the → magnetic quantum number.
Since the electron carries an electric charge, the circulation of electron constitutes
a current loop which generates a magnetic moment associated to the
orbital angular momentum.

Fr.: moment angulaire rotationnel, moment cinétique ~

The → angular momentum of a body rotating about an axis.
The rotational angular momentum of a solid homogeneous sphere of mass
M and radius R rotating about an axis passing through its center
with a period of T is given by:
L = 4πMR^{2}/5T.

An intrinsic quantum mechanical characteristic of a particle that has no classical
counterpart but may loosely be likened to the classical
→ angular momentum of a particle
arising from rotation about its own axis.
The magnitude of spin angular momentum is given by the expression
S = ħ √ s(s + 1), where s is the
→ spin quantum number. As an example, the spin of an electron
is s = 1/2; this means that its spin angular momentum is
(ħ /2) √ 3 or 0.91 x 10^{-34} J.s. In addition, the projection of
an angular momentum onto some defined axis is also quantized, with a z-component
S_{z} = m_{s}ħ. The only values of m_{s}
(magnetic quantum number) are ± 1/2. See also
→ Stern-Gerlach experiment.

Of a rotating body, a vector of magnitude ω
(→ angular velocity) pointing in the direction
of advance of a right-hand screw which is turned in the direction of rotation.