General Instructions for NVSS Image ftp service

This WWW form allows the user simplified access to images produced by the NRAO/VLA Sky Survey (NVSS). This service determines which NVSS image is desired based on a celestial position and returns a Web page with a link to the file. This avoids having to determine the name and/or directory of the file. This survey was made with the National Radio Astronomy Observatory's Very Large Array telescope at a wavelength of 20 cm (1.4 GHz) and produced images of the sky north of declination -40 deg with a resolution of 45". Both total intensity and linear polarization was imaged. The survey is now complete.

The images from the NVSS are produced as 4 x 4 degree, overlapping images. The images use the SIN projection, have 15" cell spacing and are labeled in J2000 coordinates. (The NVSS Postage stamp (small FITS file) server can be used to obtain images with other geometries.) This form will allow determination of the closest of these images to a desired position. In addition to the desired image size, the polarizations included in the returned image may be specified (see below).

Descriptions of individual fields on this form follow:


This is the equinox of the coordinates to be used for input coordinates. The NVSS FITS files use J2000 coordinates.


The returned FITS file can contain either Stokes' parameter I (total intensity) or Stokes' I, Q and U (total intensity and linear polarizations). In the former case, the returned image will have one plane; in the latter, three.

Central Right Ascension

The desired position on the sky is expressed in terms of its celestial position which consists of a Right Ascension (like longitude but expressed in hours) and declination (like latitude). The central Right Ascension at the specified equinox is given as hh mm ss.s (hours minutes and seconds of time). Values in the range 0 0 0.0 to 23 59 59.9 are valid.

Central declination

The central declination is given as +/-dd mm ss.s (degrees, minutes and seconds of arc). Values in the range -40 0 0 (the southern limit of the survey) to +90 0 0 are valid.