Astronomical Image Processing System

Lore & Background

Development of AIPS started at NRAO in 1978, two years before the VLA became fully operational. Originally written in FORTRAN 66, it has used FORTRAN 77 since 1989. The very first installation was on a MODCOMP computer, but portability led to installations on many systems; pre-compiled versions are now available for Linux and Mac OS, while Solaris users must build from source since 2018. Over the years, capabilities expanded from initial VLA focus to data from practically all radio interferometers, including MERLIN, GMRT, and to a lesser extent WSRT and ATCA. VLBI calibration (including space VLBI) was added in the 1990s, primarily for the VLBA, making it the main package for the EVN and Global VLBI. Single-dish support was added in the 1980s, notably for NRAO's 12-m and 91-m telescopes. AIPS has outlived its supposed replacement AIPS++ (rebranded as CASA), which now serves the upgraded VLA and ALMA, but AIPS remains able to process data from these instruments. Despite its age and limited resources, it remains under active development and is free software under the GNU General Public License.

Reader's Guide

AIPS runs under the X Window System with commands entered interactively via a command-line interpreter called POPS, which provides mathematical functions, logical operators, and flow control. Commands can be placed in text files for repeatable procedures and pipelines; a modern alternative is the Python-based ParselTongue interface. A typical session includes the terminal window, the AIPS TV for visualizing and interactively editing data, and the Message Server for task information. Basic plots can be displayed using TEKSRV, a Tektronix 4012-based graphics terminal. Data must be imported into AIPS's own data areas, usually in FITS format—a standard agreed in 1979 whose development is inseparable from AIPS. Over 530 individual programs perform specific tasks such as imaging, calibration, editing, and model fitting. Extensive help is available from the command line, along with the AIPS Cookbook (a user guide built around example recipes), available online and in PDF/PostScript. A newsletter, AIPSLetter, is published biannually. The name has led to primate-themed humor: the Cookbook includes banana-based recipes, the programmer's guide is called Going AIPS (cover featuring a gorilla with a Tektronix 4012 on IBM tape units), and various covers and icons include primate images.

Did You Know?

• AIPS was originally written in FORTRAN 66 and switched to FORTRAN 77 in 1989.
• The first AIPS installation was on a MODCOMP computer.
• AIPS has over 530 individual programs for data processing tasks.
• The FITS standard, agreed in 1979, is inseparable from the development of AIPS.

Pioneering the First Celestial Photographs

The story of capturing the night sky on photographic media begins with a series of bold, often frustrating experiments in the 1830s and 1840s. Louis Jacques Mandé Daguerre, the very inventor of the photographic process that bears his name, made the first known attempt to photograph the Moon in 1839. The result was a disappointing indistinct blur, a casualty of tracking errors during the lengthy exposure. Just a year later, on March 23, 1840, John William Draper—a chemistry professor at New York University who was also a physician and scientific experimenter—succeeded where Daguerre had faltered, producing a 20-minute daguerreotype of the Moon through a 5-inch reflecting telescope. The Sun followed, possibly first captured in an 1845 daguerreotype by French physicists Léon Foucault and Hippolyte Fizeau. Italian physicist Gian Alessandro Majocchi had attempted to photograph a total solar eclipse in Milan on July 8, 1842, exposing iodized plates to the thin crescent's light before and after totality. These early efforts were constrained by the limitations of the daguerreotype process, which was far too slow for anything but the brightest objects, and by the wet plate collodion method, which limited exposures to the window during which the plate remained wet.

Tracking, Guiding, and the Fight Against Light Pollution

Because the Earth never stops spinning, every serious astronomical image demands that the telescope counteract the apparent drift of stars across the sky, a phenomenon known as diurnal motion. This is achieved through equatorial mounts or computer-controlled altazimuth systems that rotate the instrument in the opposite direction of Earth's rotation, keeping the target centered for the duration of the exposure. Yet no mechanical system is perfect. Imperfect motor drives, the gradual sag of the telescope tube under its own weight, and the bending of starlight through the atmosphere all introduce tracking errors. To combat these, observers employ a guiding technique: a secondary co-mounted telescope, called a guide scope, or an off-axis guider using a prism or optical beam splitter, allows a reference star to be monitored throughout the exposure. In the earliest days, a person would stand at or even ride inside the telescope, manually adjusting a crosshair to keep the guide star centered. Today, computer-controlled systems handle this automatically in both professional and amateur setups. Additionally, because urban light pollution can swamp a sensitive detector during long exposures, imaging equipment and dedicated observatories are typically sited in remote, dark locations to preserve the faint signal from distant celestial objects.

A Scientific Revolution in Subdisciplines

From almost its very beginning, astronomical photography branched into a family of specialized subdisciplines, each with its own distinct scientific objective. These include star cartography, astrometry, stellar classification, photometry, spectroscopy, and polarimetry, alongside the discovery of new objects such as asteroids, meteors, comets, variable stars, novae, and even previously unknown planets. The field's impact on professional research was nothing short of revolutionary: by employing extended exposure times, astronomers recorded hundreds of thousands of stars and nebulae that were simply invisible to the unaided human eye. To meet the demands of these diverse tasks, ever-larger and more specialized optical telescopes were built, functioning essentially as enormous cameras designed to record images on photographic plates. Some instruments were engineered for precise imaging, others for a wide field of view—Schmidt cameras being a notable example—while still others were tuned to capture light at specific wavelengths. Modern astronomical CCD cameras can cool their sensors to suppress thermal noise and extend detection into infrared spectra, and specialized optical filters allow researchers to isolate particular bands of light. What began as a photographic novelty in the mid-nineteenth century thus evolved into the foundational imaging methodology underpinning nearly all observational astronomy today.

The Amateur Pursuit and Aesthetic Vision

Because almost all observational astronomy today relies on photographic or digital imaging, the term 'astrophotography' has gradually shifted in common usage to refer primarily to the amateur community rather than professional research. Where scientists seek precise measurements and scientific data, amateur astronomers are often driven by the desire to produce aesthetically pleasing images of the night sky. This distinction does not diminish the technical sophistication involved. Amateur practitioners employ a wide range of specialized equipment and techniques, from long-exposure photography that allows both film and digital sensors to accumulate photons over extended periods, to the use of specialized optical filters that restrict captured light to particular wavelengths. The ability to image objects far beyond the visible spectrum—dim stars, nebulae, and distant galaxies—has opened the night sky to enthusiasts who, with patience and the right gear, can reveal structures invisible to the naked eye. The field's origins in the mid-nineteenth century were shaped largely by experimenters and amateur astronomers, often called 'gentleman scientists,' who had to solve fundamental engineering problems such as building rigid telescope structures and constructing clock drives capable of maintaining a constant rotation rate. That same spirit of hands-on experimentation continues to define the community.