A vacuum phototube that is an extremelysensitive detector of light in the ultraviolet, visible, and near-infraredranges of the electromagnetic spectrum.
A surface where if a photon is emitted from one of its points the photon follows a closed orbit and returns periodically to its departure point. Such a surface exists only near sufficiently compact ob
jects where the curvature of space-time is very important. In other words, a body can take a stable orbit around a black hole provided that it moves with the speed of light. However, only photons can have such a velocity; hence the term 'photon sphere.' For a non-rotating Schwarzschild black hole, the photon sphere has a radius of R = 3GM/c2 = 3 RS/2, where G is the gravitational constant, M is the mass, c is the speed of light, and RS is the Schwarzschild radius. For a rotating, Kerr black hole, the situation is much more complex due to the Lense-Thirring effect. In that case circular paths exist for radii whose values depend on the rotation direction. More specifically, in the equatorial plane there are two possible circular light paths: a smaller one in the direction of the rotation, and a larger one in the opposite direction.
An instrument which measures the intensity and polarization or radiant energy. A photopolarimeter is a combination of a photometer and a polarimeter. (spase)
An instrument which measures the intensity and polarization or radiant energy. A photopolarimeter is a combination of a photometer and a polarimeter. (spase)
The lowest visible layer of the solar atmosphere; corresponds to the solar surface viewed in white light. Sunspots and faculae are observed in the photosphere.
The atmospheric layer of the Sun or a starfrom which continuum radiation, especially optical, is emitted to space. Forthe Sun, the photosphere is about 500 km thick.