The 2MASS Archive is an implementation of the All-Sky Data Release
from the Two Micron All Sky Survey, covering 99.998% of the sky observed
from both the northern 2MASS facility at Mt. Hopkins, AZ, and the southern
2MASS facility at Cerro Tololo, Chile.
The tables also include the Long Exposure (6x) Scan Catalogues: During the final months of 2MASS observatory operations, a campaign of targeted 'long exposure' observations was carried out during times when no previously unscanned parts of the sky were available for the main survey. These observations used the same freeze-frame scanning technique employed for the survey, but with READ2-READ1 exposures six times longer than was used for normal survey observations (hence they are referred to as '6x' observations). The 2MASS 6x measurements were intended to probe ∼1 magnitude deeper than the main survey in unconfused regions.