These images can consist of mosaics of anywhere from two to hundreds of 2MASS Atlas Images. The Atlas Images are the final 2MASS image product and are produced by combining the raw survey data frames (which were taken six-deep in any direction in the sky) into a final uniform image. The raw survey data were obtained with pixels which are 2´´ (2 arcseconds; 1 arcsecond is 1/3600 of a degree) in size. The combination of the six raw frames, which are slightly offset relative to one another, into a final image permits the final image to be presented with pixels that are only 1´´ in size. The "coadded" Atlas Images from which these Gallery images are produced are the same ones that are delivered by the 2MASS image server at the IRSA Survey Visualization and Image Server tool. This image server currently delivers slightly degraded 20:1 lossy-compressed images, because of disk space limitations. The full-resolution Atlas images can be obtained via the 2MASS Image Retrieval Service.
The colors in these images arise from assigning red, green, and blue to the three infrared "colors" in which the Survey images the sky. In analogy to color vision, blue (the shortest wavelength color) is assigned to the shortest wavelength channel for 2MASS, which is the 1.2-µm J band; green is assigned to the 1.6-µm H band; and, red represents the light detected in the 2.2-µm Ks band. Cool stars will appear redder than hot stars. Interstellar dust artificially makes distant stars appear redder (in analogy to the setting Sun). The effects of this "interstellar reddening" are particularly apparent near the edges of dark obscuring clouds of dust.
The images contain a number of artifacts produced by the camera and telescope system. Bright stars tend to be embedded in diffraction spikes (fainter crosses). These spikes were produced by light passing the cross-shaped secondary mirror support structure at the top of each telescope. Bright stars also produced trails of "persistence ghosts." This effect occurs because bright stars left a latent image on the 2MASS detector arrays. Since these pictures result from combination of many 2MASS raw data frames, and since these raw data frames were obtained as each telescope scanned smoothly in the declination (vertical on the images) direction, the "ghosts" appear as a trail of increasingly fainter images either above (north of) or below (south of) bright stars. In addition, some bright stars also produced "glint" artifacts, particularly in the Ks filter, which usually appear as fainter "stars" immediately east of north and west of south of the bright star. All of these artifacts should be taken into account when viewing the images and image mosaics.
The images and image mosaics in the various Galleries are released into the public domain. If any image or images are redisplayed or reproduced, please accompany the image or images with the following acknowledgment: "Atlas Image [or Atlas Image mosaic] obtained as part of the Two Micron All Sky Survey (2MASS), a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation." If pressed for space, this acknowledgment could be shortened to, e.g., "Atlas Image [or Atlas Image mosaic] courtesy of 2MASS/UMass/IPAC-Caltech/NASA/NSF." However, all or part of the full acknowledgment is preferred. This is the stated policy of 2MASS.
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