Here are some of our most frequently asked questions. If you don't find what you're looking for here please feel free to contact us.

Why is my search returning no results / Not seeing expected results.
   It's possible that you've provided search criteria that is too restrictive. Try hitting "Clear Search" and reduce the number of criteria. If in doubt, you can explore all holdings by performing an open-ended search with no criteria at all. The Results page provides tools for drilling down further into the data. If you're still having trouble locating data, send a help request to astroarchive@noirlab.edu
How do I open *.fits.fz files?
   Most files served by the Astro Data Archive are compressed 3-5X to minimize expense of storage and data transfer. Software tools such as Astropy, DS9, CFITSIO, and Gnuastro can work with this format transparently. More information on FITS file compression can be found here: https://heasarc.gsfc.nasa.gov/fitsio/.
Do I need an account to use the Astro Data Archive?
   An account is not needed for general public data access. Accounts are used to serve proprietary data to investigators on observing programs approved by the NOIRLab Time Allocation System. The proprietary period is usually 18 months after which data is publicly accessible.
How do I obtain the calibration data associated with observations?
   Generally speaking, instrument calibrations are done in the afternoon for one or more observing programs on a given night. Calibration files are typically identified with the OBSTYPE keyword, where OBSTYPE != 'object' (e.g dark, flat, etc..). The calibration files will not necessarily share the same pointing information as observations, and consequently may not appear in searches for a particular object.

   So, to obtain all calibration files associated with an observation, perform a separate search without any RA/DEC constraints. Search for ALL files within the observing night(s) of interest with OBSTYPE != 'object'.

Where are the complete file collections for surveys, data releases, etc..
   The Astro Data Archive endeavors to index (and make searchable), all high level science images in the NOIRLab sphere. Some file collections have not yet been indexed. Those collections are available for download here: https://astroarchive.noirlab.edu/hlsp/
Where's my data? Principal and Co-Investigator Data Access:
   Principal (PI) and Co-Investigators (Co-I) named on approved observing programs can use credentials assigned by the NOIRLab Time Allocation System to obtain proprietary data from the Astro Data Archive. The PI can delegate additional access rights at any time. Individuals that require data access to proprietary files should ask the program PI to send a request to astroarchive@noirlab.edu. These types of requests are normally handled within a business day.
Does the Astro Data Archive have an API?
   Yes. Please see Documents for a complete API description and working examples. For general metadata access, /api/find/ is a good place to start. This web service allows search on ANY FITS file field in the Astro Data Archive. /api/retrieve/ allows secure download of files or specific HDUs.
Are Virtual Observatory (VO) services available?
   Simple Image Access (V1) protocol is available through /api/vohdu/ and /api/voimg/. Please see Documents for a complete API description and working examples.