As in my Deep-Sky Companions: The Messier Objects, all the photographs in this book are reproduced in black and white. The decision was not made merely to save money. While it's possible to see hints of color in some of the brighter star clusters, nebulae, and galaxies, such objects typically manifest themselves in shades of gray at the eyepiece. Color photographs of deep-sky objects may mislead beginners into thinking that they can expect to see vivid reds, greens, and blues, when they will not.
Imagine you're a bird watcher who has never seen a raven. You want to see the bird, because the photograph in your guidebook has set your heart on fire. The raven, it appears, is a
Deep-sky objects O Open cluster □ Bright nebula (small)
ffi Globular cluster C? Bright nebula (large) <=> Galaxy (edge-on) Dark nebula O Galaxy (face-on) v Planetary nebula C'j Magellanic Clouds most striking specimen. Its beak is yellow, its head a rose-tinted aquamarine, its body olive, its wings vibrant indigo, and its tail feathers squid-ink black. You must see it! Now imagine the disappointment when you go birding with a friend, who points out the black raven. Shocked, you show your friend the photograph in your guidebook. Your friend laughs and tells you that that's a heavily enhanced image that exaggerates the iridescence of the bird's feathers. The point is, why risk disappointing new observers when we can try to help them discover the beauty of reality? Furthermore, you most likely will compare the photographs to your eyepiece views with the help of a dim red flashlight, and under such illumination a color photograph actually would be a handicap.
Whenever possible, photographs were chosen to reflect the kinds of detail an observer might see with his or her own eyes. For that reason a few photographs may appear underexposed compared to more famous views you may have seen elsewhere.
That we were able to reproduce such excellent photographs of the Caldwell objects is largely a result of the generosity and perseverance of many talented astrophotographers. These dedicated students of the night sky work much harder than a purely visual observer might imagine in order to capture their revealing images.
While we attempted to obtain high-quality astrophotos of every Caldwell object from the worldwide community of amateur astronomers, in several cases we have resorted to reproducing digitized photographs taken by enormous Schmidt telescopes in both hemispheres. These photos have been made available to astronomers and scientists worldwide by the visionary architects of the Digitized Sky Survey (DSS), which can be perused on the World Wide Web at http://archive.stsci.edu/dss/. (The copyright for the DSS photos used in this book rests with the Anglo-Australian Observatory Board, the United Kingdom Particle Physics and Astronomy Research Council, the California Institute of Technology, and the Associated Universities for Research in Astronomy; they are used here with permission.) Detailed credits appear in Appendix D.
In a few cases we have also reproduced images from the Hubble Space Telescope and large telescopes like those on Mount Wilson and Palomar Mountain. For the most part, these images are included to illustrate scientific points discussed in the accompanying essays.
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