Compare
FITS vs Zarr
FITS is a standard for astronomy data organized into Header/Data Units (HDUs). Zarr stores multidimensional arrays as chunks and metadata under keys in a store.
Which format should you choose?
Choose FITS for astronomy observations and exchange with FITS-aware archives and tools. Consider Zarr for chunk-level access to large arrays on a file system or object store.
Good fit for FITS
Storing and exchanging astronomical and scientific images, spectra, and tables
- Combining multiple data units and metadata in one dataset
- Exchanging observational data between FITS-aware tools
Good fit for Zarr
Storing large multidimensional arrays in chunks · Working with scientific data in cloud object storage
- Reading selected regions of large arrays
- Sharing sharded datasets between compatible tools
Basic information
| Field | FITS | Zarr |
|---|---|---|
| Extension | .fits, .fit, .fts | .zarr |
| MIME type | application/fits | |
| Common uses | Storing and exchanging astronomical and scientific images, spectra, and tables | Storing large multidimensional arrays in chunks · Working with scientific data in cloud object storage |
| How to open | Use an astronomy viewer, analysis program, or scientific library that supports FITS. If the file contains several HDUs, inspect extensions as well as the primary HDU, and verify coordinates, units, data type, and missing-value handling. | Use a Zarr-capable library or analysis tool. Check version, array shape, chunk grid, codecs, and attributes. Keep the whole local directory or required object-store keys and consult producer documentation. |
| Export or convert | When converting to an image, table, or another scientific format, check whether coordinate systems, units, observation metadata, and extra HDUs are preserved. Keep the original FITS and compare scientific values and positions after conversion. | When converting from netCDF or HDF5, check dimensions, types, chunks, attributes, and coordinate conventions. Preserve the source and validate values after conversion. |
Choose by use case
Combining multiple data units and metadata in one dataset
Storing and exchanging astronomical and scientific images, spectra, and tables
FITSExchanging observational data between FITS-aware tools
Storing and exchanging astronomical and scientific images, spectra, and tables
FITSReading selected regions of large arrays
Storing large multidimensional arrays in chunks · Working with scientific data in cloud object storage
ZarrSharing sharded datasets between compatible tools
Storing large multidimensional arrays in chunks · Working with scientific data in cloud object storage
ZarrKey point 1
FITS HDUs contain headers and data such as image arrays or tables; Zarr maps array and group metadata and array chunks to store keys.
More on the differencesKey point 2
FITS astronomy conventions and Zarr array attributes do not automatically preserve each other's scientific meaning.
More on the differencesMore on the differences
Use FITS where established astronomy workflows require HDUs and FITS conventions. Consider Zarr for chunked array access, but test the target Zarr version, codecs, chunk layout, and storage backend.
- FITS organizes images and tables in HDUs with headers. Zarr organizes arrays, groups, metadata, and chunks in a store.
- Coordinate systems, WCS, units, and times need explicit mapping; neither a FITS header nor Zarr attributes guarantee equivalent interpretation after conversion.
- Check extra HDUs, tables, scaling, missing values, data types, and metadata; also verify Zarr version, codecs, chunk shape, and complete transfer of all store keys.
Frequently asked questions
Can FITS be converted to Zarr without losing information?
Not automatically. Validate images, tables, extra HDUs, WCS, units, time, scaling, and other metadata in the target store.