Cosmic Background Explorer/DMR
DMR Skymap Info
The COBE sky cube is based upon the quadrilateralized spherical cube (quad-sphere) projection and the quad-tree pixel ordering scheme.
NOTE: THIS FILE DOES NOT CONTAIN SCIENCE DATA FROM A COBE INSTRUMENT. FURTHERMORE, THE COORDINATES GIVEN IN THE BINARY TABLE EXTENSION CORRESPOND TO PIXEL CENTERS AND MAY NOT BE APPLICABLE TO SOME OF THE COBE DATA PRODUCTS (SEE THE INSTRUMENT EXPLANATORY SUPPLEMENTS FOR SPECIFIC ADVICE). WHEN AVAILABLE, USE THE COORDINATES GIVEN IN THE DATA FILES RATHER THAN THE ONES GIVEN HERE.
The primary data array for this file gives the quad-sphere (QS) pixel number as a function of location on the COBE quad-sphere cube faces. The QS pixels are ordered according to the quad-tree nearest neighbor pixel numbering scheme, which is hierarchical. Because of this, the QS pixel numbers are not sequential along a row or column. This FITS file also contains one binary table extension after the primary data array. There are no other extensions. The binary table gives the coordinates at the QS pixel centers. Coordinate information is given in the binary table for various reasons. The primary reason is that the quad-tree ordering of the quad-sphere pixels is not linear. The CD matrix convention might handle this, but it is not yet a part of standard FITS. Since COBE data will be analyzed on a pixel-by-pixel basis as well as by analyzing the full sky, the binary table format seems to be the most conceptually clear. Furthermore, it is useful to give the coordinates of the pixel centers in equatorial and Galactic coordinates as well as the COBE standard ecliptic 2000, and this is readily done via the binary table format.