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THE FILE FIELD GUIDE
.fits

FITS Astronomical Data

Data & Science

FITS stores astronomical images/tables and can contain multiple HDUs with headers describing scale and coordinates. Distinguish display stretching from numerical analysis.

Main use
Store astronomical images/tables with observation metadata
Data type
Binary data
All sections, questions and sources

Content reviewed： · Editor：Kai

Opening steps

Choose your environment or purpose to see its steps.

FITS viewer / Astropy

Preserve the original and inspect a working copy in a compatible application.

  1. Open a copy in FITS-capable software and inspect the HDU list.
  2. Identify image/table type, dimensions and header information.
  3. Keep display brightness/stretch settings separate from original values.
Inspect the received file and its requirements

Establish dependencies and settings before proceeding.

  1. Identify which HDU contains the image.
  2. Inspect data type, scaling and physical units.
  3. For coordinates, inspect WCS information and observation records.

Menu labels and support vary by app, OS and version. Preserve the original before making changes.

Troubleshooting by symptom

  • Image appears black: inspect display limits/stretch.
  • No image: inspect extension HDUs and table content.
  • Orientation differs: inspect display conventions and coordinate metadata.
  • Values differ: inspect scaling, data type and export settings.

FITS → display PNG / selected CSV table

  1. Set limits/stretch for display images, or select the required HDU/columns for table export.
  2. Check HDU, array dimensions, units, coordinates and display-export settings.

PNG/JPEG do not preserve scientific value range, headers and WCS equivalently.

Inspect all relevant HDUs

An empty primary HDU can coexist with science images, errors and masks in extensions. Match each array’s meaning with producer notes and headers.

Source for these steps：NASA / GSFC · FITS Primer / Astropy project · FITS File Handling

Worked example: checks before handoff

Example: deliver the scientific FITS separately from a display PNG, recording the chosen HDU and display limits.

Source for these steps：NASA / GSFC · FITS Primer / Astropy project · FITS File Handling

Related-format differences

Related-format differences
Format / methodPurpose and preserved information
.fitsStore astronomical images/tables with observation metadata
PNG / CSVPNG conveys appearance and CSV selected tables, not the entire multi-HDU scientific dataset.
FITS → display PNG / selected CSV tablePNG/JPEG do not preserve scientific value range, headers and WCS equivalently.

Handling and security

Review sharing conditions for observation targets/unpublished research and retain originals.

Questions and answers

Are FIT and FTS related suffixes?

They can identify FITS, but FIT is also used for unrelated Garmin data.

Can I analyze a converted picture?

Display exports lose values/metadata; use original numerical data for required analysis.

Does an empty primary HDU mean corruption?

Images/tables may reside in extensions; inspect the complete HDU list.

Format facts: name, steward and MIME type
Formal name
FITS Astronomical Data
Steward / specification
NASA / GSFC
MIME type
Consult the producer or delivery system. The extension alone does not establish a MIME type.

Primary and official sources

  • Software documentationFITS Primer

    Headers and image/table HDU structure.

    NASA / GSFC · Link checked：
  • Software documentationFITS File Handling

    HDU inventory, reading, scaling and validation.

    Astropy project · Link checked：