OF THE ROGER N. CLARK

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-- VISUAL ASTRONOMY OF THE DEEP SKY -- APPENDIX E: A CATALOG OF DEEP-SKY OBJECTS 1950.0 2000 .0 Charts ID RA DEC RA DEC Con Type 2000 Uran VPSA - - - - - - - - - - - - - - - - - - - -1 - - - - - - - - - - - - - - -1 - - - - - - - - - - - - - - - -1 - - -1 - - - -1 - - - -1 - - - - 1 - - - - NGC 7510 23 09 .2 60 18 23 11 .3 60 34 Cep OpC1 3 5 8 3 9 NGC 7582 23 15 .8 -42 38 23 18 .6 -42 22 Gru SBb NGC 7590 23 16 .3 -42 31 23 19 .1 -42 15 Gru Sb 23 415 3 63 23 415 3 63 NGC 7599 23 16 .7 -42 32 23 19 .5 -42 16 Gru SBc 23 415 3 63 NGC 7619 23 17 .8 07 55 23 20 .3 08 11 Peg El 17 214 194 NGC 7626 23 18 .2 07 56 20 .7 08 12 Peg E2 17 214 194 NGC 7635 23 18 .5 60 54 23 20 .7 61 10 Cas Neb 3 23 15 NGC 7654 M52 23 22 .0 61 20 23 24 .2 61 36 Cas OpC1 3 3 9 * NGC 7662 23 23 .5 42 14 23 25.9 42 And Plan 9 88 9 1 NGC 7789 23 56 26 23 57.0 56 43 Cas OpC1 3 35 3 9 NGC 7793 23 54 .5 55 .3 -32 51 23 57 .9 -32 33 34 34 3 9 Sc1 Sd 23 350 335 ID Size v mag arc - min S.B. Cl MDM Comments . - - - - - - - 1 - - - - -1 - - - - - - - - -1 - - - -1 - - - -1 - - -1 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - NGC 7510 9. 3x3 20 .0 1.7 26 30 stars mag 10+ NGC 7582 11 .8 3.0x3 .0 22 .8 0.6 26 group with NGC 7590 , 7599 NGC 7590 11 .9 2.2xO .8 21.1 1.2 96 group with NGC 7582 , 7599 NGC 7599- 12 .0 3.8x1 .2 22 .3 0.8 64 group with NGC 7582 , 7590 NGC 7619 12 .6 0.8xO .6 20 .4 1.5 128 near NGC 7826 12 .7 NGC 7626 NGC 7635 NGC 7654 7. 12x12 2l. 0 l.3 6 NGC 7662 8.5 0.5xO .5 15 .6 3.5 154 NGC 7789 10 . 20x20 25 .1 -0.4 4 11 . 0.9xO .7 20 .8 l.4 110 10x5 23 .9 0.1 15 NGC 7793 9.7 6.0x4 .0 2l . 8 l.0 19 near NGC 7619 the Bubb le Nebula M5 2, 120 stars mag 9+ central star mag 14 900 stars mag 11+ NOTES Scl·Sys: The Sculptor System is one of the most difficult objects in this catalog to detect in any telescope. The average surface brightness is low at 26.3 magnitude per square arc-second, and even the maximum at its center is a faint 23.9. The brightness distribution is similar to some globular star clusters and probably only the central 20 arc-minutes is detectable visually in the darkest skies. NGe 1435: The Merope Nebula in the Pleiades. The surface brightness was obtained directly by O'Dell (1965), so the value listed is among the best for any of the nebulae in this book. The total visual magnitude was computed from the size and surface brightness. NGC 1499: The California Nebula is extremely low in surface brightness but can be seen under good conditions. See Sky & Telescope, December, 1982, p. 612, for a discussion of different successful observations. M24: M24 is a detached portion of the Milky Way and not an open cluster. See The Messier Album (Mallas and Kreimer, 1978) for details. ------ -- ---- -- ------ -- -------- -- -- - - - 316 317
-- APPENDIX F: OPTIMUM DETECTION MAGNIFICATIONS FOR DEEP-SKY OBJECTS -- Table F.1. Magnification causing a given suiface brightness reduction Appendix F Optimum detection magnifications for deep-sky objects Appendix E listed the minimum optimum detection magnification (MDM) for each of the 611 deep-sky objects catalogued. But that magnification is the best for an object only if it is the lowest your telescope can give. No one will be viewing each object at this power optimally, unless they happen to be using a whole battery of different-sized telescopes. For your particular instrument, what is the best power for detecting each galaxy, cluster, or nebula This appendix suggests answers. It lists the optimum detection magnification, which we will call the OD M, fo r each catalogued object in a range of telescopes under a dark country sky. Of course, if an object is bright enough and the sky dark enough, it will be easy to see at many magnifications and no calculation is needed. But if the object is a challenging one near the limit of detection, it's very helpful to know the ODM. HOW THE COMPUTATION IS DONE again. By following some simple rules the solution can be found quickly. First check that the object's total magnitude is within reach of your telescope. Use Table 4.1 or equation 4.2 to find your telescope's limiting magnitude. If the object should be detectable at all, then you can do a computation to find the ODM. The ODM depends on three things. First is the surface brightness of the background (Mo). As in Appendix E we will use Mo = 24.25 magnitudes per square arc-second for a dark coun try sky. Second is the size of the object you wish to study. Use the smaller dimension that describes the object. For example, if you are examining an elliptical galaxy, use the minor axis size. If you are examining a wisp of nebulosity, use its width, not its length. Third is the reduction in surface brightness due to the telescope's transmission factor and magnification. The first step is to make a guess at the ODM. You can use any number you wish here. To generate the entries in this appendix I simply made a first guess of lOOX. You For those who want to know how these values could use the MDM value from Appendix E. were calculated, or who wish to perform their To get close you might try using Figure 2.7b own calculations for light-polluted conditions in the following way. Add about one to the or for objects not listed in the table, the next background surface brightness Mo (for examfew pages explain the method. Other readers pie for a dark country sky try 25), then find may wish to skip this section. the angle corresponding to this value from The computation of the optimum detection Figure 2.7b (at Mo = 25 we find about 7 armagnification is a complex iterative proce- minutes). This angle divided by the object s dure ideal for a computer. The goal is to find size gives the first guess. the power that magnifies the object to the Now that we have made a guess at the optimum magnified visual angle. This sounds magnification, we need to see whether it is simple, but each time you change the tele- close. We must determine what effect the scope's magnification, the surface brightness magnification has on the object's brightn ss . of everything you are viewing also changes. Recall from Chapter 4 that magnification So to find the correct magnification you simp- dims the apparent surface brightness of anyly make a guess and then compute if that is thing seen through a telescope. To get a parcorrect. If not, you make a new guess and try ticular surface brightness reduction Mb ID a 318 ::::====- Reduction in magnitudes/sq. arc-sec Telescope 0.38 2.12 3.62 4.73 6.24 7.1 2 aperture - Magnification per inch of aperture 15.0 25.0 50.0 75.0 Inches mm 3.4 7.5 -- 2 51 7 15 4 102 14 30 6 152 20 45 8 203 27 60 10 254 34 75 12 305 41 90 14 356 105 16 406 54 120 18 61 135 20 508 68 150 24 610 81 180 30 762 101 225 457 47 36 914 121 270 40 1016 135 300 given telescope means using a particular magnification m. The relation can be easily derived by rearranging equation 4.3: m = 0. 1116 D 10 (Mtl5) , or Mb = 5 10g(m / (0.1116 D)) , (equation F.l) (equation F.2) where D is the telescope aperture in millimeters and Mb is in magnitudes per square arc-second. (If you wish to give D in inches, change the constant 0.1116 to 2.833.) Table F. l uses this formula to list the magnifications that yield certain surface-brightness reductions in various telescopes. Now compute the background surface brightness as viewed by the eye through the telescope at this power. It is found by adding the surface brightness reduction Mb from equation F.2 to the initial background Mo: Bo = Mo + Mb. (equation F.3) ow read the OMV A from Figure 2.7b Usmg this new Bo as the background surface brightness. (If you extrapolate the OMV A ey nd 27.0 mag. per square arc-sec., do not et It become greater than 360 arc-minutes, because the object is then spread over too large an area in the eye.) 319 30 50 100 150 60 100 200 300 90 150 300 450 120 200 400 600 150 250 500 750 180 300 600 900 210 350 700 1050 240 400 800 1200 270 450 900 1350 300 500 1000 1500 360 600 1200 1800 450 750 1500 2250 540 900 1800 2700 600 1000 2000 3000 A new guess for the optimum detection magnification, which for now we will simply call m, is given by m = OMVA/size (equation F.4) where "size" is the object's smallest dimension, as discussed above. If m turns out to be the same magnification that was used to compute Mb, then m is the optimum detection magnification (ODM), and you're done. More likely m will be somewhat different. In this case use the m just computed and try again until the two results match within reason. With a computer, a few iterations can quickly narrow in on a good solution. For those wishing to program this procedure into a computer you must be able to compute the curve in Figure 2.7b. Table F.2 lists specific values along that curve. Other values can be found by interpolation. If you do interpolation, you should interpolate the 10g(OMV A) values because the line curves too much using normal OMVA values. Let's work through an example. Suppose we intend to hunt for NGC 134 in an 8-inch telescope. What is the best magnification Look at Table F.3, which shows computations for this object. At iteration 1 an initial
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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
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-- VISUAL ASTRONOMY OF THE DEEP SKY
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--- -- M82 (NGC 3034), PECULIAR GAL
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-- --- --- MI05 (NGe 3379) NGe 3384
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MI09 (NGe 3992), GALAXY IN URSA MAJ
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-- --- M99 (NGC 4254), GALAXY IN CO
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== -- VISUAL ASTRONOMY OF THE DEEP
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--- --- -- NGC 4449, GALAXY IN CANE
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-- -- --- VISUAL ASTRONOMY OF THE D
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--- -- M90 (NGC 4569), GALAXY IN VI
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--- -- M94 (NGC 4736), GALAXY IN CA
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-- VISUAL ASTRON0MY OF THE DEEP SKY
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-- --- -- VISUAL ASTRONOMY OF THE D
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-- -- VISUAL ASTRONOMY OF THE DEEP
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--- -- M83 (NGC 5236), GALAXY IN HY
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--- VISUAL ASTRONOMY OF THE DEEP SK
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--- -- VISUAL ASTRONOMY OF THE DEEP
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---------------- 5 / --------______
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--- -- VISUAL ASTRONOMY OF THE DEEP
Page 115 and 116: VISUAL ASTRONOMY OF THE DEEP SKY --
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Page 121 and 122: VISUAL ASTRONOMY OF THE DEEP SKY A
Page 123 and 124: -- MI5 (NGC 7078), GLOBULAR CLUSTER
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Page 133 and 134: -- ·rl E I u L ro 5 +J Q) (f) 0 Y
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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
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Page 149 and 150: -- Appendix E A catalog of deep-sky
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Page 183 and 184: 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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