Kordylewski cloud

Kordylewski clouds, also named ghost moons, are concentrations of dust that exist at the L4 and L5 Lagrangian points of the Earth–Moon system.

[2][3][4] Kordylewski began looking for a photometrically confirmable concentration of dust at the libration (Lagrangian) points in 1951.

[8] In October 2018, the existence of the Kordylewski clouds was reported to have been confirmed by the Royal Astronomical Society,[2][3][4] even though, earlier, in 1992, the Japanese Hiten space probe, which passed through the Lagrange points to detect trapped dust particles, did not find an obvious increase in dust levels above the density in surrounding space.

[10] The decisive factor and change of methodology that has led to the unambiguous confirmation of the existence of these extremely faint and elusive celestial objects was using polarimetry, i.e. detecting them by their polarization patterns, not (primarily) by their brightness.

[11] They are very difficult to observe from Earth[7] but may be visible to the unaided eye in an exceptionally dark and clear night sky.