OF THE ROGER N. CLARK

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-- VISUAL ASTRONOMY OF THE DEEP SKY A VISUAL ATLAS OF DEEP-SKY OBJECTS . . . • --- 10'--- Photograph ofNGC 6992-5. South is up. (Courtesy Mount Wilson and Las Campanas Observatories, Carnegie Institution of Washington.) Drawing of NGC 6992-5. Note the greater detail that became apparent with the modest improvement in sky quality over the observation of 8/12/83. cale: 3.4 arc-min/cm Viewing Distance (cm) Drawing Method 2 air mass: 1.05, faintest star: 14.7 at zenith, 188x; IOX:IOI 100X:1O no trac k' mg 25X: 40 200x: 5 8/26/84 6:45-7:20 UT atJones Hill Quadrangle, 50x: 20 300x: 3 Colorado; R. Clark -Inch f/l1.5 Cassegrain 20mm Erfle (117X) l2. 7mm Erfle (334X)
VISUAL ASTRONOMY OF THE DEEP SKY A VISUAL ATLAS OF DEEP-SKY OBJECTS -- NGC 7000, THE NORTH AMERICA NEBULA IN CYGNUS. R.A. 20h 5S.Sm, Dec. 44° 20' (2000.0) Technical. NGC OO is a hug . e and beauti I mixture of emISSIOn, reflectIOn and dark :ebulae. It was first noted by William Herschel in 1]86. The whole complex is estimated to be about 2300 light-years away and about 60 light-years across. For many years NGC 7000 was thought to be illuminated primarily by 1st-magnitude Deneb, but that type A2 star produces too little ultraviolet light. Astronomers now believe that a faint star largely hidden . by nterven . ing du t provides the main illummatlOn. ThIs star IS near the "Atlantic coast". Another part of the nebular complex, lying west of NGC 7000, is known as the Pelican Nebula: IC 5067, 5068, and 5070. The Pelican and North America are actually one object; a dark cloud in the foreground merely seems to split them. Visual. The North America Nebula has an angular width of about 100 arc-minutes. Recent estimates give NGC 7000 a total magnitude of 5 and a mean surface brightness of 23.6 magnitudes per square arc-second. Its size is about 100 arc-minutes in diameter. It's often stated that NGC 7000 can be seen with the unaided eye under excellent skies. This may be because its shape is outlined by foreground dark clouds that block our view of both stars and nebulosity in the background. The many faint stars seen in the nebula itself contribute to the apparent contrast of "North America" with the surrounding sky, and their light may be what's seen with the unaided eye. The faint stars may also have biased the magnitude estimates. The nebula itself is easily visible with 7 X 50 binoculars under good skies, but the best views are under excellent skies with a telescope at about 30x. The drawing shows the view through the 8-inch's finder: a mere 2.4- inch refractor working at 7.9x. The nebula appeared as a soft glow intermingled with many faint stars. The "North America" outline was clearly visible. Through the 8-inch Cassegrain itself, the nebula could not be detected at 82 x, the lowest power tried. Under less than ideal conditions, lower power wide-field instruments are the only ones that show this unusual object. Under excellent skies, higher powers may be tried in an effort to see some of the detail within the nebula, but again, low powers yielding a field of view of at least 2° give the best overall VIew. In August 1984 I used the 3-inch finder under excellent skies of the Colorado Rocky Mountains. The North America Nebula was a beautiful sight at 31 x. It stood out like a puff of cotton among the stars. The Pelican was also faintly visible. Under such excellent conditions, detail could be detected through the 8-inch in the "Mexico-Central America" region at 82 X. That region has the highest surface brightness and contrast with the surrounding sky. 226 227
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OF THE ROGER N. CLARK
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Published by Sky Publishing Corpora
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CONTENTS M78 (NGC 2068) NGC 207 1,
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PREFACE During research for this bo
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VISUAL ASTRONOMY OF THE DEEP SKY AB
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VISUAL ASTRONOMY OF THE DEEP SKY TH
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.. .. .. .. VISUAL ASTRONOMY OF THE
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e viewed with enough magnification
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lens and a piano-convex eye lens. A
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controlled depends on how many laye
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The Lumicon H-Beta Filter (Figure 3
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every 1 ° in declination and 4 min
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error of only one quarter the field
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Table 4.1. Ideal limiting magnitude
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5 Making drawings and keeping recor
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more detail in the future. They add
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.. .. .. ... Contrast (C) C Log(C)
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VISUAL ASTRONOMY OF THE DEEP SKY A
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--- VISUAL ASTRONOMY OF THE DEEP SK
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--- M76 (NGC 650-651), PLANETARY NE
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-- -- M45, THE PLEIADES OPEN CLUSTE
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-- Brightest stars of the Pleiades
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M42 (NGC 1976), M43 (NGC 1982), THE
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--- --- --- VISUAL ASTRONOMY OF THE
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-- --- NGC 2023 NGC 2024, IC 434 (T
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--- --- M78 (NGC 2068), NGC 2071, D
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VISUAL ASTRONOMY OF THE DEEP SKY --
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--- M67 (NGC 2682), OPEN CLUSTER IN
Page 69 and 70: -- VISUAL ASTRONOMY OF THE DEEP SKY
Page 71 and 72: --- -- M82 (NGC 3034), PECULIAR GAL
Page 73 and 74: -- --- --- MI05 (NGe 3379) NGe 3384
Page 77 and 78: MI09 (NGe 3992), GALAXY IN URSA MAJ
Page 79 and 80: -- --- M99 (NGC 4254), GALAXY IN CO
Page 81 and 82: == -- VISUAL ASTRONOMY OF THE DEEP
Page 83 and 84: --- --- -- NGC 4449, GALAXY IN CANE
Page 85 and 86: -- -- --- VISUAL ASTRONOMY OF THE D
Page 87 and 88: --- -- M90 (NGC 4569), GALAXY IN VI
Page 89 and 90: --- -- M94 (NGC 4736), GALAXY IN CA
Page 93 and 94: -- VISUAL ASTRON0MY OF THE DEEP SKY
Page 95 and 96: -- --- -- VISUAL ASTRONOMY OF THE D
Page 97 and 98: -- -- VISUAL ASTRONOMY OF THE DEEP
Page 99 and 100: --- -- M83 (NGC 5236), GALAXY IN HY
Page 103 and 104: VISUAL ASTRONOMY OF THE DEEP SKY A
Page 107 and 108: --- VISUAL ASTRONOMY OF THE DEEP SK
Page 109 and 110: --- -- VISUAL ASTRONOMY OF THE DEEP
Page 111 and 112: ---------------- 5 / --------______
Page 115 and 116: VISUAL ASTRONOMY OF THE DEEP SKY --
Page 119: -- -- VISUAL ASTRONOMY OF THE DEEP
Page 123 and 124: -- MI5 (NGC 7078), GLOBULAR CLUSTER
Page 127 and 128: --- VISUAL ASTRONOMY OF THE DEEP SK
Page 133 and 134: -- ·rl E I u L ro 5 +J Q) (f) 0 Y
Page 135 and 136: -- --- VISUAL ASTRONOMY OF THE DEEP
Page 137 and 138: VISUAL ASTRONOMY OF THE DEEP SKY NG
Page 139 and 140: '2 5 -rl E I U L CO '---' -t-J ill
Page 141 and 142: VISUAL ASTRONOMY OF THE DEEP SKY AP
Page 145 and 146: VISUAL ASTRONOMY OF THE DEEP SKY Ta
Page 147 and 148: VISUAL ASTRONOMY OF THE DEEP SKY Ta
Page 149 and 150: -- Appendix E A catalog of deep-sky
Page 153 and 154: -- -- --- VISUAL ASTRONOMY OF THE D
Page 155 and 156: --- --- VISUAL ASTRONOMY OF THE DEE
Page 165 and 166: -- -- VISUAL ASTRONOMY OF THE DEEP
Page 167 and 168: -- APPENDIX F: OPTIMUM DETECTION MA
Page 169 and 170: ------- VISUAL ASTRONOMY OF THE DEE
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--- VISUAL ASTRONOMY OF THE DEEP SK
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VISUAL ASTRONOMY OF THE DEEP SKY -
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VISUAL ASTRONOMY OF THE DEEP SKY AP
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VISUAL ASTRONOMY OF THE DEEP SKY -
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VISUAL ASTRONOMY OF THE DEEP SKY Ta
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VISUAL ASTRONOMY OF THE DEEP SKY Ta
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G VISUAL ASTRONOMY OF THE DEEP SKY
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INDEX INDEX M70 (NGC 6681), 312, 31
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OF THE ROGER N. CLARK

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