Making a Sky Atlas

Appendix A Making a Sky Atlas Although a number of very advanced sky atlases are now available in print, none is likely to be ideal for any given task. Published atlases will probably have too few or too many guide stars, too few or too many deep-sky objects plotted in them, wrong- size charts, etc. I found that with MegaStar I could design and make, specifically for my survey, a “just right” personalized atlas. My atlas consists of 108 charts, each about twenty square degrees in size, with guide stars down to magnitude 8.9. I used only the northernmost 78 charts, since I observed the sky only down to –35°. On the charts I plotted only the objects I wanted to observe. In addition I made enlargements of small, overcrowded areas (“quad charts”) as well as separate large-scale charts for the Virgo Galaxy Cluster, the latter with guide stars down to magnitude 11.4. I put the charts in plastic sheet protectors in a three-ring binder, taking them out and plac- ing them on my telescope mount’s clipboard as needed. To find an object I would use the 35 mm finder (except in the Virgo Cluster, where I used the 60 mm as the finder) to point the ensemble of telescopes at the indicated spot among the guide stars. If the object was not seen in the 35 mm, as it usually was not, I would then look in the larger telescopes. If the object was not immediately visible even in the primary telescope – a not uncommon occur- rence due to inexact initial pointing – I would then scan around for it. If I did not find the object after having diligently swept the area through the primary telescope I recorded it as “not visible.” I never resorted to more detailed charts con- taining fainter guide stars in an attempt to pinpoint the object’s location more precisely – a method that in many cases enables one to see challenging objects. T. Aranda, 3,000 Deep-Sky Objects: An Annotated Catalogue, Patrick Moore’s 487 Practical Astronomy Series, DOI 10.1007/978-1-4419-9419-6, © Springer Science+Business Media, LLC 2012 488 Appendix A Making a Sky Atlas MegaStar uses a certain formula to produce its default star symbol sizes. This formula is designed for finder charts of tiny fields with guide stars all the way from 0 to 15th magnitudes. A different formula is needed to produce appropriate star sizes for charts of much larger areas of the sky and with fewer star magnitude cat- egories. The formula I settled on (through trial and error) starts with .70 mm for the smallest stars and multiplies this by 1.400 to get the next symbol size (.98). To make each larger symbol size after the second, .035 is subtracted from the previous multiplier. I set the border thickness to zero, since MegaStar otherwise enlarges and elongates all the stars. Index Magnitude Star symbol size (mm) 0–5 –2.0 – (–1.1) ´1.085 = 5.94 6 –1.0 – (–0.1) ´1.120 = 5.47 7 0.0 – 0.9 ´1.155 = 4.89 8 1.0 – 1.9 ´1.190 = 4.23 9 2.0 – 2.9 ´1.225 = 3.56 10 3.0 – 3.9 ´1.260 = 2.90 11 4.0 – 4.9 ´1.295 = 2.30 12 5.0 – 5.9 ´1.330 = 1.78 13 6.0 – 6.9 ´1.365 = 1.34 14 7.0 – 7.9 ´1.400 = 0.98 15 8.0 – 8.9 0.70 The font for the DSO labels needs to be as small as possible in order to minimize overlap with stars, object symbols, and other labels. I chose Verdana 7 point. (Now, with my older eyes, I might make the font a little larger.) If you undertake an all-sky survey, you will probably need a chart map (such as the one illustrated) to keep track of which parts of the sky you have already observed as you go along. Simply mark each piece of the sky as it is observed. My chart map shows both my atlas’s 108 charts and, for added reference, Sky Atlas’s 26 charts. The only significant drawback to a MegaStar atlas is that the DSO labels cannot be moved around to prevent overlap with guide stars. This problem, however, is much less troublesome than it might at first appear, partly because there are so many guide stars that no one is critical, and partly because stars that are run over by labels can usually still be seen anyway. In any event, the most crowded fields can of course be enlarged. In general it is a great pleasure to cruise around the sky with the aid of my cus- tomized atlas and my binocular finder. The MegaStar program incorporates the new Tycho star catalogue, which is so accurate that, unlike with my old Sky Atlas 2000.0, it is a very rare occasion when I do not see the sky through the finder exactly as it appears in the atlas. Appendix A Making a Sky Atlas 489 Cygnus 490 Appendix A Making a Sky Atlas Leo Appendix A Making a Sky Atlas 491 Sagittarius 492 Appendix A Making a Sky Atlas Virgo Galaxy Cluster North Appendix A Making a Sky Atlas 493 Virgo Galaxy Cluster South 494 Appendix A Making a Sky Atlas Quad Chart Appendix A Making a Sky Atlas 495 Chart Map The bold/double lines and numbers indicate the corresponding Sky Atlas charts. 496 Appendix A Making a Sky Atlas Appendix B Notes on Object Descriptions Notes on Descriptions of Galaxies (1) General brightness is a rough measure of visual prominence, which depends on both surface brightness and size. Hence a small galaxy with a high surface brightness and a large galaxy with a low surface brightness might both be described as “moderate brightness.” To put it another way, brightness compari- sons among galaxies are most meaningful when the galaxies are of reasonably similar size. (2) Unless they are confi rmed by other observations or photographs, involved or very nearby stars seen in any given observation might be transient (e.g., super- novae) rather than permanent. (3) Regarding multiple galaxies in a fi eld: In the case of a dominant central galaxy and a few fainter ones surrounding it, directions to the additional galaxies are usually in relation to the principal galaxy. In the case of several similar galaxies in a long string or a large group, the direction to each new galaxy is usually from the last-described galaxy. In either case the described relative positions of the galaxies are obvious enough when the observation is checked against a detailed map or photograph. References to fi eld stars within the group, however, are always in relation to the galaxy just mentioned unless otherwise stated. (4) I neglected in my very fi rst observation session – fortunately involving only a small fraction of all the listed galaxies – to record nearby stars as religiously as involved stars. In those cases where the omissions were most glaring, post- observation notes describing the nearby stars were appended in brackets. 497 498 Appendix B Notes on Object Descriptions (5) The names and relative directions of galaxies in pairs or small groups are given in corresponding order. Thus, “In the position is a double galaxy [*1588 (HH), 1587] with the components right next to each other E-W” means that 1588 is E and 1587 is W. Notes on Descriptions of All Objects (1) Small-telescope observations of bright objects in a group all appear under the brightest object. For example, 12 × 35 and 42 × 60 observations of M31, M32, and M110 are all found under M31. (2) “Plotted” fi eld stars are stars plotted in my atlas and on my large-scale fi nder charts; these are all relatively bright stars that will be found in most advanced sky atlases. (3) A number of variable stars were too faint to be well seen when I fi rst observed them. I had to observe these repeatedly until I caught them near the bright end of their cycles. In a handful of cases I never did catch the star at a reasonable brightness. (4) Regarding shape: Globular clusters are almost all essentially round, so their shape is rarely mentioned. Unless the shapes of open clusters are specifi cally described, it is to be assumed that these objects are roughly round. (5) As a rule, the degree of concentration of globular clusters is attenuated as compared to that of galaxies: a “sharply concentrated” globular cluster is not nearly as sharply concentrated as a sharply concentrated galaxy. (6) It might be wondered why I use expressions such as “at its edge E/NE/SE” rather than the more normal-sounding “at its E/NE/SE edge.” The reason is that the former expression is applicable with any object and with any direction, while the latter can be nonsensical, for instance in the case of a N-S edge-on galaxy with an E edge and a W edge but no NE, SE, NW, or SW edge; or in the case of a round object, which has only one edge – the circumference – not several directional edges. Whatever the shape of an object, the expression “at its edge E/NE/SE” unambiguously means a point E or NE or SE of center. (7) Instances of glaring discrepancies between the listed data or the NGC description on the one hand and my observation on the other are too numerous and too intractable to comment on, explain, or reconcile in every case.

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