So how many stars are there in the Universe? It is easy to ask this question, but difficult for scientists to give a fair answer! Stars are not scattered randomly through space, they are gathered together into vast groups known as galaxies. The Sun belongs to a galaxy called the Milky Way.
Reverse osmosis. Reverse osmosis (RO) is a water purification technology that uses a semipermeable membrane to remove ions, molecules, and larger particles from drinking water.
UV filter. An L39 UV filter with a 55mm filter thread. A UV filter was used to protect the lens from damage. UV filters are individual compounds or mixtures that block or absorb ultraviolet (UV) light. UV filters are used in sunscreens to protect skin or in photography to reduce the level of ultraviolet light that strikes the recording medium.