The website allows you to check the astrometry of your images, and you can correct the World Coordinate System (WCS) section of a FITS if they are missing, incorrect or inaccurate.


See the Documentation page.


You need the anaconda python 3 and the executable in your PATH.
For c/tcsh:

setenv PATH /usr/local/astrometry/bin:${HOME}/anaconda3/bin:${PATH}

For bash:

export PATH=/usr/local/astrometry/bin:${HOME}/anaconda3/bin:${PATH}


Version 0.75 was installed on Tuesday, 17 July 2018.


Check PATH is correct with the following commands:
bash-4.2$ which python
bash-4.2$ which solve-field
Copy some of the demo images and run solve-field on them:
cp /usr/local/ .


solve-field file.fits

solve-field apod4.xyls --overwrite
Reading input file 1 of 1: "apod4.xyls"...
Reading file "./apod4.axy"...
Field 1 did not solve (index index-4219.fits, field objects 1-10).

Field 1 did not solve (index index-4219.fits, field objects 11-20).
  log-odds ratio 48.9759 (1.86196e+21), 21 match, 0 conflict, 72 distractors, 35 index.
  RA,Dec = (187.157,56.7089), pixel scale 169.782 arcsec/pix.
  Hit/miss:   Hit/miss: ---++-+++++--+-+++-----------+-----+--------+----+------+----+-------+--+------------------++(best)-------
Field 1: solved with index index-4218.fits.
Field 1 solved: writing to file ./apod4.solved to indicate this.
Field: apod4.xyls
Field center: (RA,Dec) = (187.176490, 56.713419) deg.
Field center: (RA H:M:S, Dec D:M:S) = (12:28:42.357, +56:42:48.308).
Field size: 33.1504 x 23.7302 degrees
Field rotation angle: up is 50.4949 degrees E of N
Field parity: neg
Files produced are:
Output files
base-ngc.png	an annotation of the image.
base.wcs	a FITS WCS header for the solution.	a new FITS file containing the WCS header.
base-objs.png	a plot of the sources (stars) we extracted from the image.
base-indx.png	sources (red), plus stars from the index (green), plus the skymark (“quad”) used to solve the image.
base-indx.xyls	a FITS BINTABLE with the pixel locations of stars from the index.
base.rdls	a FITS BINTABLE with the RA,Dec of sources we extracted from the image.
base.axy	a FITS BINTABLE of the sources we extracted, plus headers that describe the job (how the image is going to be solved).
base.solved	exists and contains (binary) 1 if the field solved.
base.match	a FITS BINTABLE describing the quad match that solved the image.
base.kmz	(optional) KMZ file for Google Sky-in-Earth. You need to have “wcs2kml” in your PATH. See

Author, References and Acknowledgements

For academic use, please cite the paper:

Lang, D., Hogg, D.W., Mierle, K., Blanton, M., & Roweis, S., 2010, Blind astrometric calibration of arbitrary astronomical images, The Astronomical Journal 139, 1782--1800.
See the People page

Related Software

Doug Mink's imwcs software for automated WCS refinement.

John Thorstensen's automatch software for automated WCS refinement

Potential Problems

Programs were compiled on a SL7 machine, so they will not run on RedHat/Centos/SL 6 machines.
Rhys Morris
Last modified: Tuesday, 17 July 2018