The IDL Astronomy Library FAQ
This document is intended to answer the most
Frequently Asked Questions
about the IDL
Library (sometimes abbreviated Astrolib).
The FAQ is a dynamic document that
will change as
changes. Suggestions for corrections or additional
sections are welcome
please email them to Nick
A. Purpose and Organization of the IDL
A1. How can I find out about stars,
holes, galaxies etc.?
A2. I haven't purchased an IDL
license -- can
I still use
Library? Can I use it with PV-WAVE or GDL?
A3. How do I install the IDL
A4. Who supports the IDL Astronomy
A5. Which platforms and IDL versions
supported by IDL
A6. Is there an online help file
with the IDL
A7. Why are there so few widget and
programs in the Library?
A8. Are there known name
Astronomy Library and other IDL Libraries?
A9. Where can I find IDL software
A10. How is configuration control
for the IDL Astronomy Library?
A11. How should the IDL Astronomy
A12. Are there any mirror sites for
IDL Astronomy Library?
A13. Is there a E-mail distribution
A14. What is the
the IDL Astronomy Library?
B. IDL Software for Astronomy
B1. What astronomical image
B2. Are there any IDL widgets for
B3. What IDL software is available
B4. Will there be any updates to the
Purpose and Organization of the IDL Astronomy
A1. Where can I find out
planets, black holes, galaxies etc.?
Sorry, you've come to the wrong place. The IDL
collection of low-level software in the commercial
and is mainly of interest to
astronomers who already have purchased an IDL
software license. For
questions about astronomy, one good starting point
is the list of Web
available at the WEBStars
page at Goddard Space Flight Center.
A2. I haven't purchased
I still use the Library? Can I use it with
PV-WAVE or GDL?
IDL is a commercial prduct requiring a purchase of a license from
Solutions. You are welcome to use
any of the programs as
and convert them to your favorite language.
(GDL) is a free IDL compatible incremental
compiler. I have not tested most
of the IDL Astronomy
Library procedures under GDL but READFITS() and
WRITEFITS do work.
programming language with similarities to
IDL. In fact, many years
ago (1990) it was an
language to IDL, but has since
Enough time has passed that few of the IDL
Astronomy Library programs will be directly
useable under PV-WAVE.
A3. How do I install
The entire contents of the Library can be loaded
one of two
or from a .zip file at the
file maintains the procedures in separate topical
whereas the astron.tar.gz
file has the same files but with all the
procedures in a single
directory. The astron.zip
file has identical contents to astron.tar.gz but
in .zip format.
The graphics routines in the IDL Astronomy
Library make use of routines in the Coyote
Library which must be downloaded
separately. Alternatively, one
can download coyote_astron.tar.gz
which contains the subset of Coyote routines
needed by the Astronomy Library.
The procedures in the IDL Astronomy Library
placed in a directory included in the IDL
!PATH. This can
either be done at startup (using the UNIX
environment variable IDL_PATH
the Windows/Macintosh preferences file) or by
simply concatenating the
to the !PATH system
variable. Note that
procedures in the IDL Astro Library are not a
rather a collection of low-level procedures to be
incorporated with the
For historical reasons, a few IDL Astronomy
the following three non-standard system
must first be defined with the ASTROLIB
procedure (or the equivalent DEFSYS definitions).
The procedure ASTROLIB also defines a default
a FITS file JPLEPH.405 containing the JPL DE405
which is used by several routines (e.g.
JPLEPHINTERP) to compute highly
positions and velocities of major solar system
objects (including the
and the Sun). However, due
to its size,
JPLEPH.405 file is not included in the standard
.tar and .zip
of the IDL Astro Library .
the JPL procedures the following two steps are
- !PRIV - Used in a couple of the
Needs to be set when modifying a database.
- !TEXTOUT - Used in the program
the database and several other
programs. Programs which use
non-standard system variable also allow a
keyword TEXTOUT to be used
of the system variable
- !TEXTUNIT - Logical output unit number
A4. Who supports the IDL
- Copy the files in
to your /data directory
- Define the environment variable ASTRO-DATA
procedure) to point to your /data directory
The IDL Astronomy Library was originallysupported by
under a small
grant from the Astrophysics Data
Program. The first grant
was awarded in 1990 to Wayne Landsman for three
years, and the grant
was renewed in 1993
and 1996. At various times,
other people, including
Varosi, Krishna Venkatakrishna, and Joseph Lyu,
have worked part-time
At the end of November 2000, all funding
ended. The library
has since been supported on a "free time available" basis.
Many of the programs in the IDL Astronomy Library
contributed by the user
particular, Don Lindler, Craig Markwardt,
Tom McGlynn, and
Bill Thompson have made significant contributions
to the Library.
A5. Which versions and
platforms of IDL
by IDL Astronomy Library?
The programs in the IDL Astronomy Library should
all later versions of
of the IDL Astronomy library compatible with older
versions of IDL are
available in the old
directory, but these will be missing more recent
updates and bug fixes.
I currently only have access to IDL on Linux
Macintosh machines, though I try to maintain
file available for the IDL Astronomy Library?
Each procedure contains a documentation
header. This documentation
can be made into Java doc-style HTML files using the
An older method is to
use the standard IDL procedure
MK_HTML_HELP to create
.html help file, though this help file can be
use, due to its large size and lack of
alternative is to simply use
procedures on this site.
Emacs can use the excellent help facilities
incorporated into the IDLWAVE mode.
A7. Why are there
procedures in the IDL Astronomy Library?
The emphasis of the IDL Astronomy Library is on
astronomy (including FITS
I/O). The are
excellent Web sites for other aspects of IDL
the three most widely used libraries for
astronomers are those
. ) Historically, widget procedures are also
more difficult to
over different IDL platforms and versions.
A8. Are there known
between the IDL Astronomy Library and other IDL
No. Please let me know
if you find any incompatibilities.
A9. Where can I find IDL
software for a
In general, the IDL Astronomy Library does not
instrument-specific software. Check
to other IDL
Sites for IDL software for a
Please inform Nicholas
of any additions or corrections to this page.
The one exception to the "no instrument specific"
software for the
IDL Astronomy Library has been for the WFPC2 (Wide
on the Hubble Space Telescope
is made because WFPC2 was so widely used,
and there is no other site supporting IDL software
control maintained for the IDL
For those needing version control I suggest
obtaining the IDL Astronomy Library from the
Procedures in the GITHub site should mirror those in
download site . The tar
and zip files in the download site are
updated roughly every
month. (Therefore, the
ASCII file version of a procedure may be up to a
than what is found in the tar
file.) Every change is
in the "Revision History" section of the
is also recorded in the news
A11. How should the
cited or acknowledged in publication?
If extensive use is made of the IDL Astronomy
home page should be cited, or the following
1993 in Astronomical Data Analysis
Systems II, A.S.P. Conference Series, Vol. 52,
ed. R. J. Hanisch, R. J.
V. Brissenden, and Jeannette Barnes, p.
A12. Are there any
sites for the
IDL Astronomy Library?
I am not aware of any such sites. All the code is duplicated
in the GITHub
A13. Is there a E-mail
for the IDL Astronomy Library?
I have discontinued the previous mailing list
notices were so
infrequent. I will post news about major updates
to the comp.lang.idl-pvwave
A14. What is the licensing
for the IDL Astronomy
The IDL Astronomy Library procedures are available
under the BSD-2
license. If included in a
package with other
procedures, I suggest that the Astronomy Library
procedures be kept in
a separate directory. Please
contact me if you wish
to make changes to a procedures, as there is a
good chance that I would
be able to include the changes in the official
IDL Software in
are available within IDL?
I know of three sophisticated image
written in IDL, that work with FITS files and
recognize the world
coordinate systems for astronomy.
Other non-astronomical image display
widgets might also be
widget by Fred Knight is easily extensible for
Liam Gumley has been especially recommended for
images that look good both on the display and on the
- The ATV
Display Tool is an IDL program
written by Aaron Barth
modeled after the popular DS9
- The object-oriented programs XCTV, XCTV2,
in the bhill
IDL Astronomy Library
- The program
Paradigm 3) originally in the
B2. Are there any
I recommend the IDL utilities available at
site. The package contains
widgets for continuum
normalization, multiple Gaussian or Lorentzian
fittings, and equivalent
B3. What IDL software is
The IDL astro programs max_likelihood
method to determine when to stop the
IDL maximum entropy code to correct for stray
light in solar
B4. Will there be any updates
written in 1990 and was based on the 1987 version
of the DAOPHOT
Thus the code for PSF
fitting is awkward to use by modern
standards, and for
PSF-fitting I would recommend
one of the modern non-IDL packages such as
DAOPHOT II or DOLPhot
However, some of the procedures in IDLPHOT such as
a sky background, find.pro
to locate point sources, and aper.pro
to perform aperture photometry remain useful and
cannibilized. While some
updates to aper.pro
are planned (e.g. to recognize NAN values as
bad pixels, and accept an error array) there are
no immediate plans to
the PSF fitting software.
Other available IDL photometry packages include
- A PSF-fitting photometry program from
of well-sampled crowded stellar fields
A software package by D. Thilker (NMSU, 2000 AJ,
120, 3070 )
for accurate photometric characterization of H
- Marc Buie's CCD Photometry program originally
designed for solar
- Marc Buie's optimal image subtraction program
Miller et al. 2008
IDL Astronomy Library Homepage