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Articles

Interstellarum Deep Sky Guide - a personal observation

by kt4hx

Interstellarum Deep Sky Guide

Authors: Ronald Stroyan, Uwe Glahn
Publisher: Oculum –Verlag in collaboration with Cambridge University Press
Year Published: 2018

IDSA_IDSG.jpg


I am sure many will recall that the release of the English version of the Interstellarum Deep Sky Atlas (IDSA) in December of 2014, through the collaborative efforts of Oculum-Verlag and Cambridge University Press, caused a real stir in the hobby. Here was a large atlas that plotted stars to magnitude 9.5 and included a significant number of objects, to include 9,599 galaxies alone. A unique feature was the categorization of deep-sky objects by their projected visibility in 4, 8 and 12 inch apertures based on observing under skies of a 21.3 MPSAS darkness level. The IDSA also included objects of interest beyond the projected reach of a 12 inch as interesting and challenging targets. It plotted objects from a wide variety of astronomical catalogues and was seen as a viable alternative to the long running and popular Uranometria atlas.

This was somewhat revolutionary stuff, though the Herald-Bobroff AstroAtlas (Australia, 1994) attempted a scaling scenario many years earlier. Their approach was different in that they utilized multiple sets of charts of increasing depth to accomplish their scaling process, in a fairly large, but nicely laminated package. Unfortunately this effort went out of print in 2002, with a brief reprise when an American company (Lymax) bought the rights and issued a small run of them after which it disappeared for the final time. It can sometimes be found on the used market, exactly where I found mine.

We now fast forward to October 2018 when the companion book to the IDSA was published, the Interstellarum Deep Sky Guide (IDSG). I wrote a review of the IDSA in August of 2015, and felt I should follow up with one of its accompanying guide. I admit that initially I was unfazed by the announcement and release of the IDSG. Reading others perceptions of it and seeing some photos of the layout, I concluded at that time it was not something I would have much use for in my observing. But as Christmas 2019 approached and I was asked for some ideas, well I saw an opportunity to add to my astronomy library, even if I didn’t think it would be beneficial to me personally. So I tossed the desk edition of the IDSG out there as an idea, and magically it appeared under the tree and now in my hands.

I thumbed through it briefly that morning, and again, felt that while it was a pretty volume and the concept interesting, it was not likely something I would utilize in the field. That said, I had already told some that I would give it a more intense going over in conjunction with the IDSA and write a review of the guide. With an upcoming business trip after the holidays, I saw that as a fine opportunity to do just that. I also bought a new copy of the IDSA field edition to take along with the IDSG as my first copy is battle worn from the field, with pages falling out and marks all over them. So that is where we are today, and it is time to share with you my thoughts about the IDSG, how it relates to the IDSA, and in my view its true utility as both a desk and field reference. So with that, let’s get into what the IDSG is all about and what it may or may not do for you.

General Overview

The main difference between the IDSA and the IDSG is that the latter is in no way an atlas, nor is it portrayed as such. In fact you will find no conventional charts in the guide. It consists solely of page after page of images and some sketches depicting and cross-referenced to a list of target objects plotted on the specified chart within the atlas. The flow of the guide tracks the flow of the IDSA, from chart 1 through 114. The number of objects depicted and the resulting space dedicated from each individual single and double page charts in the atlas varies upon the richness of the respective field and the authors’ selective process. However, they range from as few as six objects to as many as 37 (chart 45 – the Virgo Galaxy Cluster field), and devoted space from a single page of the double page format up to three full double page spreads (six total pages).

The chart number reference is found in the upper left hand corner of the left facing page and in the upper right hand corner of the right facing page. The list of target objects will appear vertically along the right hand side of a page as applicable. Below this list one will see a small rectangle with numbered circles within. This locator legend denotes the approximate place upon the specified chart one should find the object in the IDSA. See the image below for an example of this presentation.

Chart 45a Example.jpg


The guide starts out, as in the IDSA, with a short two page introduction where the authors lay out their format. They explain to the reader the philosophy behind the IDSG and that they have selected a total of 2,362 targets from all those plotted in the atlas. Continuing they state that the intent here is not simply to provide a list of the biggest and brightest objects. Rather, to concentrate on the “coolest” (their word) targets, and omit many bright but “boring” (again their word) objects. Therefore, as they indicate, they have instead included many fainter, but more interesting DSOs. Their intent here is to cover a wide range of objects from open clusters to quasars, and from very bright to very dim objects. From my optic they are basically attempting to serve up a smorgasbord of objects in an attempt to provide something for everyone and their aperture, skill and interest level.

Again, the targets are sorted throughout the IDSG by the charts upon which they are located (1 through 114), in keeping with the layout of the atlas. The targets are graphically portrayed in 1,729 bi-color composite images primarily from the Palomar Observatory Sky Survey (POSS) coupled with 821 field sketches done by the authors. In some cases more than one of the targets is found within a single photo/sketch because of positional proximity. Specifically regarding the drawings, they do caution that these are not normal eyepiece impression sketches. Rather they are highly detailed renderings that are the result of extended observations ranging from 30 minutes to several hours utilizing apertures of 4 to 48 inches. They annotate the sketches with their respective initials (“rs” or “ug”) along with the aperture and magnification utilized.

The authors also put forth some basic advice on how to locate objects within the guide, as well as the interpretation of the images and drawings. They briefly discuss maximizing your visual results with a small and very basic table about the relationship between magnification levels, exit pupils and eyepiece focal lengths at the f/4 and f/5 focal ratios. Following the introduction is a list of catalog abbreviations utilized that will look familiar to IDSA users since it is the same one that follows the chart key pages in the atlas.

We now enter into the real contents of the IDSG. Opposite of the list of catalog abbreviations at the end of the introduction section, the right facing page contains the objects selected from chart 1 of the IDSA, which is the North Polar Region. Looking at the example below, one sees that the chart number is placed in the upper right corner and immediately below it is a declination of +90° and 0h 00m along the right edge of the page. This indicates the coordinates at the center of chart 1 in the atlas. This is provided as a quick reference location guide for those who already know the position of an object of interest. Each chart’s section in the guide will carry this information at the outer edge of each page below the corresponding chart number to aid the observer in quickly finding the correct page(s).

Located on this first page we find a group of six images of the six selected targets for this chart, numbered 1 to 6. In this case, there are only two accompanying sketches for this target list, specifically for object #2 (IC 3568) and #5 (Arp 204). Here we get into an issue that I will discuss in detail later – errors. The sketch for Arp 204 is actually labeled as being object #4, which is nothing more than the North Celestial Pole (NCP). But the sketch matches up with image #5 (Arp 204) rather than image #4 (NCP). While this is an unfortunate error, it is a minor one that is easily recognized. Quite frankly, in my opinion, selecting the NCP as one of the targets was not a particularly good choice since it is not an object at all. Rather it is simply a marker representing a specific place in the sky. I find it more of a curiosity than something to turn one’s scope toward. Again, that is just this reviewer’s opinion.

IDSG Chart 1.jpg


Looking at the above image of the IDSG page for chart 1 in the atlas, along the right side of this page one will find the list of objects selected and sorted by their projected visibility in the scaled system utilized within the IDSA. In this case they list four objects as “visible in 4-inch telescopes” (again under 21.3 MPSAS skies). Image #1 contains the galaxies NGC 2276 and NGC 2300. Image #2 and sketch #2 is the planetary nebula IC 3568 and image #3 shows the open cluster NGC 188. The next level of objects are categorized as “Challenges for big telescopes”, which contains the pair of interacting galaxies in Arp 204 (image #5 and sketch #5 incorrectly labeled as #4 as mentioned above) and the single galaxy NGC 3172 (image #6). The final item is listed as a “Special object”, which is the NCP (image #4).

Each line item in this list of objects contains its primary identifier and object class (two letter abbreviation – OC, Gx, PN, etc.) and the three letter abbreviation for its resident constellation. They also include some limited additional information that can vary from object to object, but may contain (but not necessarily) things such as alternate IDs, visible appearance, sub-type of object, recommended magnification level, filter recommendations, and other miscellaneous clarifying data. This same layout is repeated chart by chart throughout the IDSG, to highlight those objects that the authors selected for our attention.

After making our way through all the coverage, chart by chart, we come to the end of the guide where the authors have provided two indexes. The first is termed an “Index of deep-sky-objects with nicknames.” Here the authors list the nicknames utilized for some of the objects covered in the IDSG in alphabetical order with columns for the primary catalog designation, chart and object number, visibility class (4, 8, 12 inch or C for challenge), object type and constellation. This is followed by the larger “Index of deep-sky-objects by catalog numbers”, which is all the objects found in the IDSG. They are sorted by their respective primary catalog designation in alphanumeric order, also including the chart/object number, visibility class, type and constellation. On the very last page after the object indexes they include a list of constellations with their three letter abbreviations, and a short list of errata for the IDSA.

My Impressions

A reviewer’s impressions of a book are, of course, their own and theirs alone. Therefore I cannot state how others will view the utility of the IDSG as it relates to the IDSA or as a standalone volume. But I can hopefully impart to you my honest impressions based on my years of experience as a deep sky observer, lover of printed atlases and observing guides in general, and owner/user of many such publications.

As I indicated to you, my first impressions when I heard about the release of the IDSG, read some initial reviews and viewed some images of its contents, was relatively flat to be honest. While I saw the contents to be interesting and attractive to the eye, I was less than enthused about its true utility for myself, and perhaps some others. I certainly was not excited about it as compared to the IDSA, which has been my primary field atlas for the last five years. Though the IDSA certainly is not perfect, as no atlas is, it is still a handsome and superbly useful atlas. So much so that my original desk version is but a shadow of its former shiny self, displaying the exhaustive use I’ve put it through. But that is what I expect of a trusted friend that has served me well. But I digress, so back to the matter at hand, the IDSG.

After having some time to really go through and study the contents of the guide, I feel I have a pretty good sense of what it is, and how useful it would be for me. My initial reticence while not totally overcome has abated as I’ve had the opportunity to intimately familiarize myself with the volume. That said, all is not rosy here, and I will address that soon enough.

First let me say that I have come to find that the IDSG is something that I could utilize in the field depending upon my agenda for a given session. I do not however see it as something that I would need to carry outside with me all the time. However, it would most certainly warrant a spot on my observing table from time to time when I am targeting some more challenging fields where the images/sketches could prove useful.

Because I am a hardcore galaxy hunter, its coverage of many challenging objects, to include several Abell Galaxy Clusters, Arp Peculiar Galaxies and Hickson Compact Galaxy Groups truly piqued my interest. The applicable images and sketches included could be beneficial for identification of dim and/or crowded galaxy fields. But it reaches beyond that as well. Other classes of objects could also benefit from the images and sketches as aids to their detection and identification.

I could also see some folks planning their observing solely around the contents of the IDSG, and they are the ones who are more likely to carry it into the field on a regular basis. Therefore, for those folks the utility of the IDSG is much more profound, because it could become a constant companion. I believe that is truly the primary concept that the authors had in mind when the project was conceived and completed.

As an observing guide it has its utility. However, as with any atlas, no one observing guide or companion does everything correctly. For example, I am very fond of the Deep Sky Field Guide (DSFG), the accompanying volume for the Uranometria atlas. It is infinitely useful and cover to cover contains a massive amount of data. However, even as much as I like looking at object data and numbers, admittedly it is a painfully dry read. Containing no illustrations and only the actual data (magnitude, size, surface brightness where applicable, actual coordinates and modest notes) pertaining to every object plotted in the Uranometria, it is not for everyone. However, it is a volume that I refer to frequently both before and after observing.

The IDSG, while limited in scope as far as the numbers of objects plotted in the IDSA, gives the objects it does include a closer, more intimate look. However, one of its downfalls, in my estimation, is that it is too void of basic data for those objects it does cover. I would have liked to have seen the authors include magnitude, size, surface brightness (where applicable) and the object’s coordinates. For my money, that information is the bare minimum that should be presented.

Granted by its design, space is limited because of the format of including images and sketches. Trying to do that for every object in the IDSA would simply be cost and size prohibitive. So utilizing the chosen format for a reasonably large select group of objects is the better option. Then again, someone will almost inevitably question some of the choices made in the selection process. That is always the danger of going the route they did with the format. But I do not do that here (other than for the NCP), as it is the author’s prerogative and I respect that.

So overall, my feelings are to the warm side about this project. I like the concept, and I like the presentation, with some reservations. I sincerely wish that they had included the basic data for each object. While the idea of a locator legend employed is somewhat useful, it still imparts a general location on the respective chart. Including the legend is fine, but also take that extra step of providing the object’s coordinates to aid the observer in tightening up their search. To be bluntly honest, had they included the coordinates, the need for the legend would fall by the wayside for me personally.

In the end, I see the utility for this volume, but it be will variable based upon the individual and how they would apply it to their observing. I applaud the authors for their diligence and hard work to bring the IDSG to the hobby, and I believe it will become useful to a lot of people during their nightly adventures.

The Issues

As I mentioned earlier, all is not rosy with the IDSG, and to be quite honest, I was very surprised by the number of errors that I found during my cursory checks of its content. Unfortunately I suspect that there are additional miscues that I did not spot, and that others will in most likelihood find additional ones as they use the guide.

All books have typographical errors, and/or sometimes data errors or transposed numbers here or there. Such things seem to slither through the editing and proofreading processes prior to publication. Simple miscues such as the one I pointed out in the overview section where chart 1 had the incorrect cross-referencing between image and sketch is something that can easily be recognized and forgotten by the reader. However, I have some real issues with a few of the ones I found and they generally lead me back to the omission of coordinates and the heavy reliance upon the locator legend.

I happened upon some of the errors by chance, which led me to pay closer attention to those particular pages, which in a few cases led me to further errors. Admittedly I have not scoured every single page of the IDSG and their associated chart within the IDSA intently. But when an error was spotted during my cursory look-through, then that focused my attention more to the specific page/chart in question. In fact I hadn’t noticed the error with the image/sketch cross-reference for chart 1 until I was writing that section of this review.

What I will do here is list the errors I found, both small and large, with some illustrations. This is not done to shine an unfavorable light upon the IDSG or authors, rather to alert those who already have it or are thinking about buying it, to some of the issues they might run across. Frankly, and this is strictly my opinion here, I find some of the errors to be beyond the occasional boo-boo that happens in writing. I can make a mistake here with spelling or grammar and most times people either don’t notice or truly don’t care. But when you are publishing an observing guide whose purpose is to “guide” the observer in their quests, and you charge the amount of money that these volumes cost, I feel it is a reasonable expectation that at least the larger errors have been scrubbed from the final product. So with that said, let’s take a look at what I managed to find during my review.

Chart 3: Object #13 (HCG 84) is listed in Draco, but is actually in Ursa Minor. Plotting on chart legend is accurate, which when one looks at the actual chart in the IDSA the error will be easily recognizable.

Chart 5: Object #5 (IC 2574) on page 5a is listed as being in Draco, but it is actually in Ursa Major. Plotting on chart legend is accurate, which when one looks at the actual chart in the IDSA the error will be easily recognizable.

Chart 18: Object #11 (NGC 6582-1) description in list states “Companion NGC 6582-1 to E.” This should read “Companion NGC 6582-2 to E.” This is obviously just a minor typo. Other data and legend position are correct.

Chart 36: Object #11 (AGC 568) marker on legend is missing. See image below where I have added the missing marker (red). Having the coordinates in the guide would have alleviated any difficulty in finding the object in the atlas.

IDSG Chart 36 Errata.jpg


Chart 37: Not an issue really, but the marker for object #2 (M36) is not circled. This could have been a matter of de-cluttering the view or simply an oversight. The numeral is correctly placed in the chart legend.

Chart 47: Image #3 misidentifies the galaxy NGC 2093 as NGC 2907. The H-II region NGC 2905 within the galaxy is properly annotated. The object list entry for the object is correct as is its legend marker. Not a significant error and easily spotted.

Chart 69: Image #17 (HCG 62) on 69b has labeling errors (see below image with my corrections in green). Though the correct data is readily available, it seems these errors come from the RNGC (and in some cases the MCG and PGC). My research which is derived from multiple sources all agree with the below corrected identifiers for the four components of Hickson 62. The labels for this galaxy group in the IDSA are also a bit out of whack as well. As background on this William Herschel discovered NGC 4759 as a single object, whereas his son John later resolved it as two separate objects and thus was eventually given two identifiers (4776 and 4778) though the original (4759) remained in the NGC.

A. NGC 4778 (this is the SE part of the double system NGC 4759)
B. NGC 4776 (this is the NW part of the double system NGC 4759)
C. NGC 4761
D. NGC 4764

IDSG Chart 69b Errata.jpg


Chart 70: Here we have a missing marker in the legend and misplacements of others. See the two scans below, one from the IDSG and the other a corrected legend I made to illustrate the discrepancies.

Please note that I will apologize here because each of my corrected legends are not necessarily scaled equally. I created them in a very basic program by eyeballing it and therefore they are not uniform one to another. But they still get the point across.

1) Object #14, Crater GC or Laevens 1 marker not shown on the chart legend. However, its relative position seems to be indicated by object #13 on the legend.
2) Object #13 (NGC 3290) is in fact in Hydra as per the target list, but its correct legend marker is mislabeled as #12.
3) Object #12 (Arp 338) is properly described in table as being in Sextans. However, its position in the legend is marked incorrectly as object #11.
4) Object #11 (MCG -2-28-45) is properly described as being in Crater, but its location marker is in the wrong position. Its marker is found in Sextans at the true position of object #12. The actual position in the legend for object #11 is not indicated but should be an overlapped circle with object #8.

IDSG Chart 70 Errata.jpg

Chart 70 Legend_Corrected.jpg


Chart 78: This chart is split into three sections in the IDSG, 78a, b and c, but the issue noted pertains only to 78a and 78b. Here they erroneously utilize the object designation #9 in both. On 78a, object #9 is for HCG 86 and on 78b they utilize #9 for objects within the image of Messier 8. Both are correctly plotted in the legend, however, the one on 78b should have been #10 in keeping with the normal sequencing of the IDSG layout. This is not a big deal because it does not really confuse the reader. It is merely something I noticed, and both are properly placed in their respective chart legends.

Chart 81: The legend marker for object #9 (NGC 5124) was mislabeled as #7. The true marker for object #7 (AGC 3574) does appear in its proper location to the left side of the left page of the legend. The marker near the center of the left page of the legend using #7 should be #9 and is properly placed. This is a source of minor confusion.

Chart 85: In the legend for this chart we have one missing marker and another misplaced. See images for original and corrected legend for comparison

1) Object #8 (UGCA 1120) marker missing from legend. However, marker for #10 is in the correct spot for #8.
2) Object #10 (ESO 362-12) marker is incorrectly placed at the position for #8 as above. However, there is no marker in the legend denoting its correct position in the IDSA chart. It should be next to (east) the marker for object #11.

IDSG Chart 85 Errata.jpg

Chart 85 Legend Corrected.jpg


Chart 91: This chart legend far and away has the most issues of any I found. The first part, chart 91a, has no issues. However, 91b is seemingly in general disarray. Rather than trying to summarize each error I recommend you compare the scan of the legend for chart 91b with my corrected version. In this case the chart legend is a bit of a mess and I am uncertain how that many mistakes could have been made survived the editing process.

IDSG Chart 91b Errata.jpg

Chart 91b Legend Corrected.jpg


Chart 101: Marker #12 (IC 4974) is plotted twice on the chart legend. The correct position is the one on the left page. The marker #12 on the right page of the legend does not denote any object in the target list for this chart and can be ignored.

Chart 104: This chart is split into two sections in the IDSG, 104a and 104b. The issues below pertain to 104b which contain targets 10 through 23 These are all errors within the supplemental data in the object list for that page.
1) Object #10 (NGC 3766) is listed as being in Carina when in fact it is in Centaurus. The legend marker is correctly placed.
2) Object #11 (NGC 3699) is listed as being in Carina when in fact it is in Centaurus. The legend marker is correctly placed.
3) Object #12 (NGC 3918) is listed as being in Carina when in fact it is in Centaurus. The legend marker is correctly placed.
4) Object #13 (Fg 1 ) is listed as being in Carina when in fact it is in Centaurus. The legend marker is correctly placed.
5) Object #17 (NGC 2944/8) is listed as being in Carina when in fact it is in Centaurus. The legend marker is correctly placed.
6) Objects #16 (Gum 39 and IC 2872) are both listed as being in Carina when in fact they are in Centaurus. The legend markers are correctly placed.
7) Object #18 (Gum 41) is listed as being in Carina when in fact it is in Centaurus. The legend marker is correctly placed.
8) Objects #21 and #23 (Hoffleit 38 and 39 respectively), the reader is instructed to see close-up chart D4 in the IDSA. That is incorrect as they are within the field of D9, rather D4. Also, while they do appear on IDSA chart 91 proper, they are not labeled there, only on D9.

Final Thoughts

I truly do not wish to give the wrong impression here regarding the IDSG. While there are several errors listed above that I spotted during my general review of the volume, most that I ran across were not significantly challenging to overcome. However, I do feel that it seems someone dropped the ball during the process of editing and reviewing the contents for that many errors to have made it through to publication.

In general, I believe the key here is too much reliance upon utilizing a chart legend rather than simply providing the coordinates for each target. While it is true that errors could be made in the coordinates, I feel it is a much easier task to simply extract that data from a reliable source than to cobble together the general locator legend that may or may not be useable. Even if one wishes to utilize the locator, it is advisable to include the coordinates and basic object data for the use and benefit of the observer. Too much information is far better than too little.

Having said all that, I do believe the idea of the IDSG is a solid one. It should prove very useful for many observers, though perhaps less so for some others. I do not dismiss it out of hand by any means, as I might have when I first learned of its publication. But again the true utility does lie in the eyes and hands of the beholder.

In terms of the target selection process, we could debate that subject until the cows come home. But in my view, to do so would prove useless. In this volume they draw our focus to a very wide sampling of he wonders portrayed within the IDSA. To that end I feel they did an excellent job of trying to provide a bit of something for everyone’s tastes. When one considers that there is a total of 14,835 Deep-Sky Objects plotted in the IDSA and that the authors whittled that down to the 2,362 presented in the IDSG, then the enormity of the project becomes clear.

To conclude this review, I will not tell you to buy it or not to buy it, as that is your own personal decision. Despite the issues that I have noted, I am still quite happy that I own this handsome volume. I believe that when I choose to target something found within its covers, it will prove very useful to my efforts. While it will not see the light of night every time I venture out, it will undoubtedly be there with me from time to time. That I can promise you!

The authors are both supremely experienced and qualified observers whom I respect enormously. The Herculean effort expended by them to bring the IDSG project to fruition as an intrinsically linked follow-on to the popular IDSA, is worthy of our respect and gratitude. While opinions may vary, there is no disputing their love of astronomy and their desire to share their wealth of experience and knowledge with all of us, so that we to may enjoy the wonder of the universe no matter our experience, our equipment or our station in life.

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