CRTS FAQ

We currently serve images from the Catalina Sky Survey (CSS). The data hosted here come from CSS Schmidt telescope located on Mt. Bigelow, obtained from 2003 to 2012. Select fields were typically visited four times a night and the median total number of visits over the ~10 year span is 20.

1) What is the format of the CRTS images?

Each image is in FITS format served as a gzip compressed file with extension .fits.gz.

2) What does the filename of the images stand for?

An example filename is : 01_10JAN06_FA0601_0004_cutout_1521.fits.gz.

  • 01_ stands for the sequence (or set number).
  • 10JAN06 is the date of observation in YYMMMDD format.
  • FA0601 is the field identifier.
  • 0004 refers to the fourth observation in the sequence. cutout_1521 is the cutout matrix location.

3) What is a cutout?

To ease the serving of images, each CRTS image is divided into 1156 smaller images called cutouts.

Each cutout is about 120 X 120 pixels and has an average size of 20 KB.

Each cutout covers an area of ABOUT 5 x 5 arcminutes.

4) What is the size of the image in pixels and area coverage of an original CRTS image?

A CRTS image is 4110 x 4096 pixels and covers an area of 29,500 square arcminutes.

5) How many images can I download?

There is currently no limit on the number of images that can be downloaded. However,the number of images returned as a result of a query will be limited by the 5 arcminutes restriction on the search radius.

6) How much area on the sky is covered by the CRTS survey?

CRTS covers thirty three thousand square degrees of the sky. A coverage map is given below.

7) How many epochs are there in the survey?

Between 4 and 400 depending on location.

8) When is the SERVICE under maintenance and what is the downtime?

The service might be under maintenance on every Monday between 9:00 A.M to 12.00 P.M (IST/ UTC+5:30). Any inconvenience caused is regretted.

9) I am facing issues with how the WCS is being interpreted in the downloaded images. What is wrong?

The images served are cutouts derived from larger images. Thus the WRA and WDEC keywords refer to the original image centre's RA and DEC and any calculation based on assuming these to be that of the centre of the cutout will yield incorrect results. Further, ds9 users are advised to check the version being used and ensure it IS NOT between 7.0 and 7.2. Please read the following update from the ds9 web page.
"DS9 version 7.0 to 7.2 may incorrectly read Linear WCS. Please use version 6.2 until beta release 7.3b3 is available."

10) What about data from the MLS and SSS?

This site currently serves only CSS data, but we do intend to expand it to include SSS and MLS in the future. Please check back later.