1 Introduction

 1.1 GAIA and SkyCat

While the incidental scraps of theogony in Homer name Okeanos ‘Ocean’ as the origin of the gods (theôn génesis), in Hesiod it is Earth (Gaia) who gives birth to Heaven (Ouranos) and then marries him; they engender the Titans, among them Okeanos and Kronos [Saturn in the Roman interpretation].

Comparative Mythology,
Jaan Puhvel, 1987.

GAIA (Graphical Astronomy and Image Analysis) is an interactive astronomical image display and analysis tool, broadly similar to SAOIMAGE (for which see SUN/166[14]). It includes a comprehensive suite of facilities for displaying and manipulating images (panning, zooming, setting the colour table etc). It also has extensive facilities for the astronomical analysis of images, including: astrometric calibration, automatic object detection and aperture, optimal and surface photometry (see Section 3). GAIA can display two-dimensional spectra, but has no facilities for specifically spectroscopic analyses.

GAIA can access images in most of the data formats common in astronomy, including Starlink NDF files and FITS images (see Section 4). It can also retrieve copies of remote images and catalogues via the Internet.

This cookbook is an introduction to GAIA. It describes the facilities that GAIA provides and gives some simple examples of their use. It refers to GAIA version 2.6 or higher. The structure of the cookbook is:

Part I
– introduction and getting started with GAIA,
Part II
– a set of recipes describing in detail how to perform some useful tasks with GAIA.

The cookbook is aimed at astronomers who are new to GAIA, but who think that it might be useful in their work. It is complemented by the GAIA User’s Manual, SUN/214: GAIA – Graphical Astronomy and Image Analysis Tool[8], which gives detailed information about the tool. Experienced users of GAIA are more likely to find this latter document useful than the present cookbook. Extensive on-line help information is also available from within GAIA itself.

1.1 GAIA and SkyCat

GAIA is a customisation and enhancement of the SkyCat1 image display tool developed by Allan Brighton and colleagues as part of the ESO2 VLT3 project. GAIA’s basic display and remote catalogue and archive access facilities are largely the original SkyCat. However, the facilities for astronomical analysis, such as astrometric calibration, object detection and photometry are all enhancements unique to GAIA. Many of these enhancements are implemented by causing GAIA to automatically invoke conventional Starlink packages (such as PHOTOM for photometry; see SUN/45[10]) ‘behind the scenes’. However, the user just sees seamless interaction through the GAIA GUI (Graphical User Interface). Also, GAIA can access images in a wider range of data formats than SkyCat (see Section 4).

1http://archive.eso.org/skycat/

2http://www.eso.org/

3http://www.eso.org/vlt/