OF THE ROGER N. CLARK

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-- -- VISUAL ASTRONOMY OF THE DEEP SKY A VISUAL ATLAS OF DEEP-SKY OBJECTS • • • • • 2'· -- Photograph oJ the inner region oJ M42, the Trapezium area. South is up. (Courtesy Lick Observatory') Drawing oJ M42 Trapezium area. Scale: 0.5 arc-min/cm 8-inch f/ 1 1.5 Cassegrain 12.4mm Erfle (l88X) Viewing Distance (cm) 100 X :69 200 x :34 300 x :23 400 x: 17 air mass: 1.17, faintest star: 13.5 at zenith, 188X; no tracking 1/13/83 9:30-9:55 UT at Hawaii Kai, Hawaii; R. Clark 104 105
-- --- NGC 2023 NGC 2024, IC 434 (THE HORSEHEAD NEBULA) NEBULAE IN ORlON le 434: R.A. 05h 41.1m Dec. -020 24' NGC 2023: R.A. 05h 41.7m, Dec. -020 13' NGC 2024: R.A. 05h 41.9m, Dec. -or 50' (2000.0) Technical. The 2nd-magnitude star Zeta Orionis, the easternmost one of Orion's belt, is surrounded by bright and dark nebulae. The region is famous for the photographically spectacular Horsehead Nebula, B33. This is dark dust cloud remarkably like the head of a ghostly horse rearing up in silhouette against the bright background of the emission nebula IC 434. The energy source illuminating IC 434 is the star Sigma Orionis, about 10 southwest of Zeta. IC 434 appears to be colliding with, or perhaps burning its way into, a very large, dark cloud. The sharp, nearly straight boundary between them extends about 10 south of Zeta Orionis. The Horsehead, about halfway down the boundary's length, is a protuberance of the dark cloud. The boundary extends about 18 light-years from north to south, and the Horsehead is about I lightyear across. The dark cloud covers the entire eastern part of the drawing and photograph, as can be seen by the relative absence of stars on the right, and in fact it extends many degrees still farther east. The whole complex has been placed at a distance of about 1200 light-years. NGC 2024 is a complex nebulous patch about 15 arc-minutes east-northeast of Zeta Orionis. It is an emission nebula, probably excited by Zeta, crossed by a large, dark lane running north to south. NGC 2023 is a bluish reflection nebula surrounding an 8th-magnitude star a little less than half a degree farther south, eastnortheast of the Horsehead. Visual. NGC 2024 is the brightest and easiest nebula in this fascinating region. It is very close to 1.8-magnitude Zeta Orionis, so placing the bright star out of the field of view reduces glare. NGC 2024 shows considerable detail in medium size telescopes, and under good skies it is visible through the 3-inch finder at 31 X. Through the 8-inch the main dark lane could be seen, along with several VISUAL ASTRONOMY OF THE DEEP SKY 106 smaller ones, as shown in the drawing. In a 13-inch telescope, many more dark appeared. lanes NGC 2023, a diffuse patch around an magnitude star, is quite easy to 8th. see if the optics are clean and free of dew. The best Way to check whether the nebula is real, than starlight scattered in the rather atmosphere telescope, or eye, is to examine other stars of of "nebulosity". IC 434 is very faint and considered one of the most difficult deep-sky objects to observe visually. It is often said that excellent skies and an 8- to 12-inch telescope at low power are required. The Horsehead, B33, is even more difficult, being only 5 arc-minutes across. Many amateurs find the dark lane in NGC 2024 and believe they've found the Horsehead. Glare from Zeta Orionis is one reason for failing to detect IC 434, especially with dirty or dewed optics. Low power is another. Medium powers not only make IC 434 and B33 larger but also increase their apparent distance from Zeta Orionis. As can be seen in the drawing with the 8-inch telescope, le 434 and B33 were detected under only moderate to good skies. The drawing by Ray Fabre using a 13.I-inch Dobsonian telescope at nearly the same powers shows a much better view of both. This view of the Horsehead is similar to that in an 8-inch under excellent skies. If good to excellent skies can be found, the Horsehead Nebula should be fairly easy in a 6-inch telescope. I have also seen it - similar brightness to make sure they are free through the 3-inch at 50X under the excellent skies of the Colorado Rockies. surface brightness measures of either NGC Unfortunately, there are no magnitude or 2024, NGC 2023, or IC 434. However, le 434 is slightly harder to detect than the Merope Nebula in the Pleiades. The average surface brightness of that nebula is 21.6 nitudes per square arc-second, so IC 434 probably 22 or slightly fainter. • • A VISUAL ATLAS OF DEEP-SKY OBJECTS • '. • • • -- 20' --- • • Drawing oJ NGe 2023, NGe 2024, and le 434 by Ray Fabre with a 13-inch Dobsonian reflector at 60x and 90x . Note the increased detail seen with the larger aperture compared with the 8-inch drawmg, . made at the same time and site. The scale and Vlewmg d' t IS ances are the same as that Jo r the 8-inch drawing. .' • . . • • 107 • • • air mass: 1.1, faintest star: 15.2 at zenith, 90 x; no tracking 2/1 2/83 7:15-8:00 UT at Waianae Ranch Hawaii' R. Fabre ' ,
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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
Page 9 and 10: VISUAL ASTRONOMY OF THE DEEP SKY AB
Page 11 and 12: VISUAL ASTRONOMY OF THE DEEP SKY TH
Page 13 and 14: .. .. .. .. VISUAL ASTRONOMY OF THE
Page 17 and 18: e viewed with enough magnification
Page 21 and 22: lens and a piano-convex eye lens. A
Page 25 and 26: controlled depends on how many laye
Page 27 and 28: The Lumicon H-Beta Filter (Figure 3
Page 29 and 30: every 1 ° in declination and 4 min
Page 31 and 32: error of only one quarter the field
Page 33 and 34: Table 4.1. Ideal limiting magnitude
Page 35 and 36: 5 Making drawings and keeping recor
Page 37 and 38: more detail in the future. They add
Page 39 and 40: .. .. .. ... Contrast (C) C Log(C)
Page 41 and 42: VISUAL ASTRONOMY OF THE DEEP SKY A
Page 47 and 48: --- VISUAL ASTRONOMY OF THE DEEP SK
Page 49 and 50: --- M76 (NGC 650-651), PLANETARY NE
Page 53 and 54: -- -- M45, THE PLEIADES OPEN CLUSTE
Page 55 and 56: -- Brightest stars of the Pleiades
Page 57 and 58: M42 (NGC 1976), M43 (NGC 1982), THE
Page 59: --- --- --- VISUAL ASTRONOMY OF THE
Page 63 and 64: --- --- M78 (NGC 2068), NGC 2071, D
Page 65 and 66: VISUAL ASTRONOMY OF THE DEEP SKY --
Page 67 and 68: --- 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 107 and 108: --- VISUAL ASTRONOMY OF THE DEEP SK
Page 109 and 110: --- -- VISUAL ASTRONOMY OF THE DEEP
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---------------- 5 / --------______
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--- -- VISUAL ASTRONOMY OF THE DEEP
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VISUAL ASTRONOMY OF THE DEEP SKY --
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-- VISUAL ASTRONOMY OF THE DEEP SKY
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-- -- VISUAL ASTRONOMY OF THE DEEP
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VISUAL ASTRONOMY OF THE DEEP SKY A
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-- MI5 (NGC 7078), GLOBULAR CLUSTER
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--- VISUAL ASTRONOMY OF THE DEEP SK
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-- VISUAL ASTRONOMY OF THE DEEP SKY
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-- ·rl E I u L ro 5 +J Q) (f) 0 Y
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-- --- VISUAL ASTRONOMY OF THE DEEP
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VISUAL ASTRONOMY OF THE DEEP SKY NG
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'2 5 -rl E I U L CO '---' -t-J ill
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VISUAL ASTRONOMY OF THE DEEP SKY AP
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VISUAL ASTRONOMY OF THE DEEP SKY Ta
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-- Appendix E A catalog of deep-sky
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--- -- VISUAL ASTRONOMY OF THE DEEP
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-- -- --- VISUAL ASTRONOMY OF THE D
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--- --- VISUAL ASTRONOMY OF THE DEE
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-- -- VISUAL ASTRONOMY OF THE DEEP
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-- APPENDIX F: OPTIMUM DETECTION MA
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------- 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 -
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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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