Most of the nearest stars are intrinsically so faint that they can be seen only with the aid of a telescope. Most of the brown dwarfs in the local neighborhood have not yet been discovered

The masses of stars can be determined by analysis of the orbit of binary stars—two stars that orbit a common center of mass. In visual binaries, the two stars can be seen separately in a telescope, whereas in a spectroscopic binary, only the spectrum reveals the presence of two stars.

brown dwarf — an object intermediate in size between a planet and a star; the approximate mass range is from about 1/100 of the mass of the Sun up to the lower mass limit for self-sustaining…. spectroscopic binary — a binary star in which the components are not resolved but whose binary nature is indicated by periodic variations in radial velocity, indicating orbital motion. nearest stars — intrinsically so faint that they can be seen only with the aid of a telescope. binary stars — two stars that revolve about each other.