Galaxies are massive systems of stars, gas, and dust bound together gravitationally as a single unit of matter. It has been estimated that the Universe includes more than 40 billion galaxies, spread around in complex large-scale structures, such as clusters, superclusters, and the boundaries of large, empty regions called voids. Our Sun is part of what we call the Milky Way Galaxy, which is a highly flattened spiral galaxy containing more than 400 billion stars. With large telescopes, we can see galaxies in all directions populating even the remotest regions of the Universe.

Understanding galaxies is an important part of modern astronomy. Galaxies are fundamental units of matter in space, and determining how they formed and achieved their current state is of critical importance to many issues in astronomy. It is significant that much of what is known about galaxies began with a simple classification of their appearance as seen on direct photographs taken with large observatory telescopes. Galaxies present a wide variety of forms, or morphologies, and can be naturally divided into categories in much the same way as living organisms can be divided into genera and species. Although galaxy morphology presents problems for classification that would not be encountered in biological taxonomy, visual galaxy classification continues to be useful at a time when galaxies have never been better understood. Classification provides order to the daunting variety of forms even if we do not yet fully understand how all the different forms came about. Classification also provides a framework for further studies and suggests a logical approach to studying galaxies.

This basic value of visual galaxy classification prompts the need for atlases that illustrate clearly the types of galaxies that are found and how to apply the notation used to describe these types. In 1959, Gerard de Vaucouleurs (1918-1995) published a galaxy classification system that is still widely used by modern astronomers. De Vaucouleurs was one of the 20th century's leading astronomers, and made many important contributions to extragalactic astronomy and cosmology (see section 10 of this website), including work on galaxy morphology. His classification system was a revision of an earlier one by Hubble (1926), but his point of view had a number of advantages over Hubble. De Vaucouleurs' classification system provided a better description of what a galaxy looks like without being too unwieldy. His approach gave greater emphasis and more accurate recognition to specific details that have a bearing on the way galaxies evolve. He published large catalogues summarizing classifications and other basic information for tens of thousands of bright galaxies. These advantages have made de Vaucouleurs' system the most-used galaxy classification system today. However, a major disadvantage of his system is that no galaxy atlas has ever been prepared that illustrates his notation and point of view. Hubble's view has been illustrated in two atlases (Sandage 1961; Sandage and Bedke 1994). This means that most astronomers use the de Vaucouleurs system without really understanding it.

We are preparing a new galaxy atlas that will document the de Vaucouleurs revised Hubble galaxy classification system with modern digital images. The principal goals are to make the de Vaucouleurs revised Hubble system more accessible and more understandable to modern astronomy researchers, students, and amateurs, and to directly connect the system to other aspects of morphology that have come to the forefront since de Vaucouleurs published his ideas. The atlas will also describe what has been learned about the features defining galaxy morphology since the 1950s. So much has been learned since that time that galaxy morphology is no longer the purely descriptive subject it used to be. This means that the proposed atlas will not only be a picture atlas, but it will also be up-to-date on our understanding of the physical processes that underly galaxy morphology. Finally, by exclusively using images from electronic detectors, it will be the first major galaxy atlas geared to illustrating classical galaxy types using today's standard imaging methods, as opposed to photographic plates.

The need for the Atlas is becoming increasingly felt as modern technology provides more and more high quality images of galaxies seen from a vast range of distances and times. De Vaucouleurs' classification system was originally defined with blue light images of nearby galaxies. This was because nearby galaxies are bright, easily observed, and show the most detail. Nearby galaxies are also being seen at a time, negligibly different from our own, when they have achieved a steady state in their structure and are changing very little. However, because of modern technology, we can now see very distant galaxies at a similar level of detail as the nearby ones de Vaucouleurs used. Galaxies at extremely large distances (several billion light years, where 1 light year is the distance light travels in one year) are being seen as they were when the Universe was considerably younger than it is now. It is expected that the morphology of galaxies would undergo significant changes during their formative period, and it is likely that very distant galaxies are showing the structures they had before a steady state had been achieved. The great value of the proposed Atlas will be in the description it will provide of normal galaxies in equilibrium, where gravity has run its course and things have for the most part settled down. Interpreting the morphologies of distant galaxies requires a thorough understanding of the features that characterize nearby galaxies as much as it would require an understanding of galaxy formation.

The atlas will be titled ``The de Vaucouleurs Atlas of Galaxies'', and will be so named to honor de Vaucouleurs' contribution to the field. This is in the spirit of ``The Hubble Atlas of Galaxies'', which was prepared by Allan Sandage in 1961 in honor of Edwin Hubble. The three of us preparing the atlas are all former students or coworkers of Gerard de Vaucouleurs who have extensively studied and used his classification system over many years. In the remaining sections of this proposal we review the basics of galaxy classification, what the de Vaucouleurs system has offered for extragalactic research, and how we will prepare the actual atlas.