Historically-aware NGC/IC Positions and Notes


Here are current versions of my NGC/IC position and notes files. I have finished my main sweep through the catalogues, checking identifications and finding accurate positions from modern sources. Most recently, I have added Gaia EDR3 positions for over 17,100 of the included objects in these files. As always, I update these files at irregular intervals. Check back occasionally for updates. Latest updates:

What's new.

My addition of the Gaia positions is essentially complete with Gaia EDR3. While the Gaia team has started work on DR4 as I write this, I will be updating only those positions NOT appearing in Gaia DR1/2/3, if any. The EDR3 positions are Good Enough for my work. DR3, by the way, will not be introducing any new positions, proper motions, or parallaxes -- the values in EDR3 are definitive -- at least until DR4 arrives!

As I have noted elsewhere on these pages, Brian Skiff and I have "selected" 16816 Gaia EDR3 positions, 80.1% of the 20997 objects represented in the position files. EDR3 positions are also given for another 290 objects, though positions from other sources better represent their location on the sky. This is usually due to the DR3 position being "pulled off" the nucleus by nearby superposed stars, HII regions, or other knots. It is possible, of course, that my assessment of the object's position is simply wrong. This particular problem, however, will not affect an object's identification unless a serious blunder is also present. I hope you'll send me any of these bugs that you find!

As I wrote previously, I am now turning to other data: detailed types, diameters, magnitudes and colors, radial velocities, and other relevant data. This led to my work on bringing the data for the RC3 galaxies up to date; see the RC3 directory for the latest on that. I've prepared a new version of RC3 with accurate positions for all the included galaxies, as well as other revised data.

I will of course be on the lookout for bugs still lurking in the NGC/IC files. One that lately came to light is that IC 809 is identical to IC 3672. This suggests that I need to compare IC1 to IC2 to search for additional identities.

Some of this introduction from a few months ago is still relevant, so here it is, updated as needed.

What's here:

If you want the main portion of all this -- including my extensive comments about nearby objects, original positions, cross-identifications, some magnitudes and diameters, and so forth -- just download the *.all and *intro.html files. You'll also want at least one set of the mean position files, too, probably the J2000.0 set (ic2000.pos, ngc2000.pos, and notngc2000.pos), though the B1950.0 set may still be of some historical interest for comparing with the mid-twentieth century catalogues I started working with in the early 1960s. See the NGC/IC positions introductory file for more information.

As I mentioned above, if you need positions and identifications for just the NGC and IC objects themselves, you may download ngconly.dat and iconly.dat, both in this directory.

If you are as interested in the history of the discovery of these objects as I am, or if you are curious why I chose the object I did to carry the NGC or IC number, then you will want to consult the Notes files: Notes on the NGC objects and Notes on the IC objects.

The current file layout still carries a hint of historical baggage. I started the project over three decades ago on computers with small and slow RAM and hard drives, so working with short files and 80-character lines was not just more efficient, it was even necessary. I also worked in the equinox B1950.0 as that was the reference equinox for virtually all of my sources. In March of 2014, I finally switched to J2000.0, and now work in that equinox with all 7840 NGC objects in a single file, and all 5386 IC objects in another. The 80-character line limit has been broken, too, at least in the position files. Aside from that, the format remains the same as it has been for the past third of a century.

All the files are 7-bit ASCII, by the way, with UNIX line-endings. I work now on a Macintosh running OS X, version 10.11.6, "El Capitan". This gives me access to almost all of my long-time UNIX tools as well as the GCC Fortran compiler (I'm currently using version 6.1.0) for building the tools and programs I use to manipulate the data.

Creative Commons License
NGC/IC Positions and Notes by Harold G. Corwin, Jr. is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.

This means that you are welcomed to use the Positions and Notes in any way you like (and you may correct any mistakes!), but please do acknowledge their origin. And if you find mistakes, please do let me know so that I can fix them, too.


Data and Images

Scattered throughout the J2000.0 base files and the notes files are data (primarily types, magnitudes, and diameters) and cross-identifications for the NGC/IC objects. The most recent data addition (aside from the Gaia DR2 positions) has been for the clusters and nebulae in the two Magellanic Clouds. Unlike the data given in the various catalogues I've authored and co-authored over the years, these data are neither complete nor homogeneous. I shall get to this eventually.

In the meantime, if you need data beyond identifications and accurate positions for the NGC and IC objects, you will want to consult

Note that a few of Wolfgang's identifications are different from mine. Compare the positions for an object to be sure that it really is the same one in each list. If they are different, please read my notes for my interpretation of the problem.

Finally, I am pleased to call your attention to Courtney Seligman's Celestial Atlas pages featuring images and notes for many celestial objects, including NGC and IC objects. In particular, many of the images -- some processed by Courtney himself -- are not only beautifully spectacular, but demonstrate the essential characteristics of the objects very well. Courtney is also tracing the history of every object; this is a welcomed and independent check on the work that those of us involved in the NGC and ICs have done over the past decades.

Latest update, this file: 17 August 2021.