How to open .FTS files on Mac
To open .FTS files on Mac, install a FITS-capable viewer listed by NASA (for example, SAOImage DS9) and open the file using File → Open inside the app.
Step-by-step instructions
- Install a FITS-capable viewer listed by NASA (for example, SAOImage DS9) and open the file using File → Open inside the app.
- If Finder does not know how to open it, Control-click the file → Open With → select the FITS viewer.
Common issues
The .FTS file won’t open or shows as an unknown format
Many default photo viewers do not support FITS/FTS, so the OS may not know which app to use.
- Open the file in a FITS-capable viewer (NASA’s FITS viewer page lists common FITS software, e.g., SAOImage DS9).
- If it still fails, confirm the file is actually a FITS file (FTS is commonly used for FITS, but the extension alone is not a guarantee).
The image looks blank, very dark, or has strange contrast
FITS pixel data often requires scientific scaling/stretching; it may not display well with default settings.
- In your FITS viewer, adjust display scaling/stretch (e.g., different autoscale options) to reveal faint detail.
- Check the header metadata and data type handling; some files contain high dynamic range or non-visual data arrays.
The file opens but metadata/headers look confusing
FITS headers use standardized keyword/value cards and can be extensive and technical.
- Use your FITS tool’s header viewer to inspect keywords and comments; this is the canonical metadata for the dataset.
- Refer to the FITS standard documentation for header structure and keyword conventions.
A program reports the FITS file is corrupted or non-compliant
Incomplete downloads, transfer issues, or non-standard writers can produce files that strict readers reject.
- Re-download or re-copy the file using a reliable method and verify it was fully transferred.
- Try opening with another FITS-capable tool/library (many software stacks use CFITSIO, which is widely used for FITS reading/writing).
Security note
FITS/FTS files are data files (not executable), but they should still be treated as untrusted input: malformed files can trigger bugs in complex image/data parsers. Prefer opening unknown .FTS files with well-maintained FITS tools.