Space Telescope Science Institute
Intro to HST Data Handbooks 8.0 May 2011
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Introduction to the HST Data Handbooks > Chapter 3: Analyzing HST Data > 3.1 Analysis Options for HST Data

HST data can be manipulated with several different software packages. In this section we introduce a few of the software language options.
STSDAS is an IRAF package developed by STScI for the reduction and analysis of HST data. The package contains tasks that perform a wide range of functions supporting the entire data analysis process, from reading tapes, through reduction and analysis, to producing final plots and images. Sections 3.2 through 3.7 introduce the basics of STSDAS, illustrating how to display HST data, presenting some simple data manipulations, and pointing you towards more sophisticated tasks.
STSDAS is layered on top of the Image Reduction and Analysis Facility (IRAF) software developed at the National Optical Astronomy Observatory (NOAO). Any task in IRAF can be used in STSDAS, and the software is portable across a number of platforms and operating systems. To exploit the power of STSDAS, you need to know the basics of IRAF. If you are not already familiar with IRAF/PyRAF, consult the IRAF/PyRAF Primer in Chapter 4 before reading further.
PyRAF is a command language for IRAF that is based on Python. It has a number of advantages over the IRAF CL. Most importantly, with few exceptions, it allows use of exactly the same syntax as the IRAF CL. Some of the advantages that it provides are:
can script IRAF tasks in Python language
Since PyRAF is so highly compatible with the IRAF CL, virtually all of the examples shown in this handbook will work the same for PyRAF. Minor differences include the user prompt and the graphics windows appearance.
More information on PyRAF can be found at:
Python is used for astronomical data reduction applications. It is a freely available, general-purpose, dynamically-typed interactive language that provides modules for scientific programming and is used for astronomical data reduction application. These modules include:
PyRAF: run IRAF tasks from Python
Python is a very powerful language that is well suited to writing programs to solve many needs beside scientific analysis. Tools are available to read (but currently not write) GEIS files.
Python can make use of PyRAF to allow access to IRAF tasks. Tutorials are available which illustrate the use of Python for interactive data analysis in astronomy (in much the same style as is now popular with IDL). The initial focus of these tutorials is the use of interactive tasks for the novice user. The more advanced tutorials focus on teaching the details of Python programming. The tutorials can be downloaded from:
STScI is developing most of its new calibration and data analysis software in Python. More information on the use of Python to analyze HST data can be obtained from:
IDL is an array-based, interactive programming language that provides many numerical analysis and visualization tools. It is typically much easier to develop new analysis and visualization applications and utilities in IDL than in Fortran or C. As a result, it is very popular in the astronomical community with many astronomers using it for their analysis of HST data.
It can be obtained from ITT Visual Information Solutions (, for a fee. Libraries for reading HST data are part of the freely available ASTRON library ( which has links to other IDL astronomy libraries.
For those who wish to write their own Fortran or C applications, we recommend using the FITSIO library for reading FITS files (; note that the C library is called CFITSIO).
This library does not support GEIS format directly so users will need to use the waivered FITS format obtained from the archive and manually extract the needed information.
The most widely used FITS libraries for Java are the Java FITS Utilities ( and the Java FITS Class Library ( These libraries do not support GEIS format, but can handle waivered FITS format.

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