Visual Astronomy of the Deep Sky

20mm Erfle 8-inch f/11.5 Cassegrain air mass amateur angle aperture appears Appendix arc-min arc-min/cm 8-inch arc-minutes astronomers background brighter brightest called central Chapter charts Clark cluster color compute contrast Courtesy dark deep-sky detail detection diameter drawing dust equation Erfle excellent eyepiece faint fainter faintest star field field of view Figure filter finder focal galaxy give given Glob Hawaii higher inches known larger lens less light light-years limit magnification magnitudes per square mean surface brightness Messier million minutes nebula needed nucleus object Observatories observing OpC1 Optical optimum Photograph PRINT region Scale scope seen side skies South spiral arms square arc-second stars mag Table Technical tele telescope tion tracking Viewing Distance cm visible visual wavelengths zenith