There are between 14 and 26 small galaxies confirmed to be within 420 kiloparsecs (1.4 megalight-years) of the Milky Way, though not all of them are necessarily in orbit. Of those, the only ones visible to the naked eye are the Large and Small Magellanic Clouds, which have been observed since prehistory. Measurements with the Hubble Space Telescope in 2006 suggest the Magellanic Clouds may be moving too fast to be orbiting the Milky Way. Of those galaxies confirmed to be in orbit, the largest is the Sagittarius Dwarf Elliptical Galaxy, which has a diameter of 20,000 light-years (6,100 pc) or roughly a fifth that of the Milky Way.
Satellite galaxies that orbit, from 1,000 ly (310 pc) of the edge of the disc of the Milky Way Galaxy, to the edge of the dark matter halo of the Milky Way at 980 kly (300 kpc) from the center of the Galaxy,[NB 1] are generally depleted in hydrogen gas compared to those that orbit more distantly. This region is the dense hot gas halo of the Milky Way, which strips cold gas from the satellites. Satellites beyond this region still retain copious quantities of gas.
The Sagittarius Dwarf is in the process of being consumed by the Milky Way, and is expected to pass through it within the next 100 million years. The Sagittarius Stream is a stream of stars in polar orbit around the Milky Way leeched from the Sagittarius Dwarf. The Virgo Stellar Stream is a stream of stars that is believed to have once been an orbiting dwarf galaxy that has been completely distended by the Milky Way's gravity.