Kirchhoff's law of thermal radiation rarefied material such as air, or transparent material, through which observations can be made. The interface is not a material body and can neither emit nor absorb. It is a mathematical surface belonging jointly to the two media that touch it. It is the site of refraction of radiation that penetrates it and of reflection of radiation that does not. As such it obeys the Helmholtz reciprocity principle. The opaque body is considered to have a material interior that absorbs all and scatters or transmits none of the radiation that reaches it through refraction at the interface. In this sense
A-235 anti-ballistic missile system eliminates the use within the limited armed conflict and other situations of this kind; secondly, the system must be mobile, without a rigid binding to any object or center; thirdly, it must provide interception at an altitude of at least 500–750 km, that is, at Low Earth Orbit] . A-235 anti-ballistic missile system A-235 PL-19 "Nudol" () is a Russian anti-ballistic missile and anti-satellite weapon system in development. This system is designed to deflect a nuclear attack on Moscow and important industrial regions. The main developer of the system is JSC Concern VKO Almaz-Antey. The new system should replace the