OF THE ROGER N. CLARK

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VISUAL ASTRONOMY OF THE DEEP SKY A VISUAL ATLAS OF DEEP-SKY OBJECTS -- M33 (NGe 598), GALAXY IN TRIANGULUM R.A. Olh 33.9m, Dec. 30° 39' (2 000.0) Technical. M33 is one of the . f ur spiral laxies in the Local Group, but It IS a small ga e estimated to hold fewer than 20 billion o ; s co ropared to the 300 billion or so in the ndromeda Galaxy (M31). M33 is about 40 000 light-years across and tilted 55° from edge-on. It is probably only about 700 000 light-years fr m M3 1, which w uld appear three times bIgger from a planet m M33 than from Earth. M33 is about the same distance from our galaxy as M31 or possibly a little closer. It was discovered by Messier on August 25, 1764, and today is ften called the Triangulum Galaxy or the Pmwheel. Visual. M33 is about I ° across, including the faint extensions, but it has a low surface brightness. Amateurs often miss it because they are looking for a smaller object. With a total magnitude of 5.3, its average surface brightness is a dim 22.8 magnitudes per square arc-second. M33 is a challenge to the novice. Experienced observers seem to have little trouble finding it, and it can even be seen with the naked eye under excellent skies. The brighter portions cover an area 20 by 30 arc-minutes. Within 1° of the nucleus are many NGe and le objects, the brightest of which is NGe 604. This is an H 11 region (a cloud of ionized hydrogen), similar to the Great Nebula in Orion but much larger, with an embedded star cluster. NGe 604 can be seen as a round spot at the end of the spiral arm to the northeast of the nucleus; it is at lower right in the drawing. I have seen it in the 3-inch finder at 89x. Most observing guides recommend very low powers for M33. Although low powers are fine for locating it, they will not show any detail. This probably accounts for the galaxy's often-reported lack of features. Medium powers (lOOX to 200x on an 8-inch telescope) will show the two main spiral arms and NGe 604 even under only moderately good skies. Excellent dark country skies should show a wealth of detail with careful observation using only a 6-inch telescope. 76 77
--- VISUAL ASTRONOMY OF THE DEEP SKY A VISUAL ATLAS OF DEEP-SKY OBJECTS • • -- 5'--- Photograph oj M33. South is up. (Courtesy National Op tical Astronomy Observatories') Scale: 1.9 arc-min/cm 8-inch f! 11.5 Cassegrain 20mm Erfle (117X) 12.4mm Erfle (188X) Drawing oj M33. Viewing Distance (cm) 25 X:72 50X:36 lOO X : 18 200 X :9 300X:6 400x:5 air mass: 1.03, faintest star: 13.8 at zenith 188X' no tracking " 9/5/83 12:00-12:50 UT at Hawaii Kai, Hawaii; R: Clark 78 79
Page 1 and 2: OF THE ROGER N. CLARK
Page 3 and 4: Published by Sky Publishing Corpora
Page 5 and 6: CONTENTS M78 (NGC 2068) NGC 207 1,
Page 7 and 8: 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 45: VISUAL ASTRONOMY OF THE DEEP SKY A
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 and 60: --- --- --- VISUAL ASTRONOMY OF THE
Page 61 and 62: -- --- NGC 2023 NGC 2024, IC 434 (T
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 101 and 102:
-- VISUAL ASTRONOMY OF THE DEEP SKY
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VISUAL ASTRONOMY OF THE DEEP SKY A
Page 105 and 106:
Page 107 and 108:
--- VISUAL ASTRONOMY OF THE DEEP SK
Page 109 and 110:
--- -- VISUAL ASTRONOMY OF THE DEEP
Page 111 and 112:
---------------- 5 / --------______
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Page 115 and 116:
VISUAL ASTRONOMY OF THE DEEP SKY --
Page 117 and 118:
Page 119 and 120:
Page 121 and 122:
Page 123 and 124:
-- MI5 (NGC 7078), GLOBULAR CLUSTER
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Page 127 and 128:
Page 129 and 130:
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-- ·rl E I u L ro 5 +J Q) (f) 0 Y
Page 135 and 136:
-- --- 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
Page 151 and 152:
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-- -- --- VISUAL ASTRONOMY OF THE D
Page 155 and 156:
--- --- VISUAL ASTRONOMY OF THE DEE
Page 157 and 158:
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-- APPENDIX F: OPTIMUM DETECTION MA
Page 169 and 170:
------- VISUAL ASTRONOMY OF THE DEE
Page 171 and 172:
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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
Page 185 and 186:
INDEX INDEX M70 (NGC 6681), 312, 31
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OF THE ROGER N. CLARK

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