iraf

IRAF (Image Reduction and Analysis Facility) is a general-purpose software system for astronomical data analysis that was developed at the National Optical Astronomy Observatory (NOAO) and distributed to the astronomical community. It provided an integrated environment for reducing, calibrating, analyzing, and visualizing astronomical images and spectra.

The core of IRAF is a command-line driven shell known as the Command Language (CL). Users invoke tasks—applications written as CL procedures or external programs packaged into libraries—and can combine them into pipelines or scripts. The software is organized into packages, such as noao for common astronomical data handling, imred for image reduction, and specialized packages for spectroscopy (onedspec, twodspec) and image analysis, among others. IRAF handles FITS data files and supports many instrument-specific reduction routines, enabling broad applicability across instruments.

IRAF operated primarily on Unix-like operating systems and was ported to other platforms. It became a widely used standard in optical and infrared astronomy for data reduction and analysis due to its extensive ecosystem of tools, even though the learning curve could be steep.

In the 2000s and early 2010s, development slowed as the community shifted toward modern scripting languages and Python-based ecosystems. Official development and distribution of IRAF effectively ended in the early 2010s; PyRAF, a Python interface to IRAF, was introduced to ease use with Python but has since been discontinued. While some legacy data can still be processed with IRAF, researchers are increasingly advised to migrate to contemporary software such as Astropy, DS9, and other Python-based tools.

IRAF remains a historically influential platform in astronomical data analysis, illustrating early efforts to provide an integrated, extensible environment for image and spectral data reduction.