Plate Solve an Astrophotograph

Plate Solving

Plate Solving makes possible the calculation of the celestial coordinates of any pixel in an astrophotograph. Alternatively, lists of known objects can be marked on the image. To Plate Solve an astronomical image stars in the image are compared to a catalog of known stars. If a pattern of stars in the image is found in the catalog, coordinates for the image center point and the image pixel scale are calculated and inserted into the FITS file.

To Plate Solve a FITS file, upload the file to Astrometry.net for automatic Plate Solving, no user inputs are required. Astrometry.net returns a FITS file with additional coordinate mapping header fields.


Aladin Sky Atlas Overlay

Once an image has been plate solved, Aladin Sky Atlas can load the plate solved FITS file, download data from an object catalog (this example used NED) and mark the objects on the image. Aladin has a built-in scripting language that can filter and highlight specific objects. Other useful object catalogs are SIMBAD and USNO.


Aladin Sky Atlas Filter

Once a Plate Solved FITS image is loaded into Aladin Sky Atlas, Aladin Sky Atlas can invert the black and white pixels. A filter can be applied to mark specific objects. It this example image a filter marks all galaxies brighter than mag 20.0 as red ovals. The Aladin Sky Atlas filter for this image for NED data is:

   ${Type}="G" && ${Mag}=="1*" { draw red oval }

Type and Mag are column names in the NED data set, G includes galaxies, 1* includes objects < mag 20.0. The magnitude field in this data is a string.


NGC 1672, Plate Solved