Last updated 20 August 2009

  • Brief overview
  • Extra datasets on the CD
  • What programs can make use of these disks?
  • Can I make copies of these disks?
  • Why you probably don't really want GSC-ACT
  • Price list
  • Order form
  • Brief overview: I am now set up to provide copies of the GSC-ACT catalog on two CD-Rs, at the cost of reproduction and shipping.

    For about nine years, the Astronomical Society of the Pacific has distributed the older GSC-1.0 and GSC-1.1 catalogs, also on two CD-ROMs. These older catalogs were under copyright, and cost about $50. However, it appears ASP has discontinued sale of these CD-ROMs.

    A few years ago, I posted an inquiry on the Minor Planet Mailing List, asking if anyone would be interested in getting GSC-ACT on two disks. The data is in exactly the same format as the older datasets on the ASP disks; only the positions have been changed slightly, to remove systematic errors that affected GSC-1.1. This means that any software that used GSC-1.1 disks from ASP can now use these disks instead.

    I got requests for about 20 sets, and have set up my PC to start grinding them out. The prices in the order form basically reflect the costs of the disks and of postage.

    Extra datasets on the CD: After storing GSC-ACT, there is still about 60 MBytes of room left on each disk. Since there's no real benefit to leaving a disk partly empty, I've tried to fill out this space with some datasets of interest that haven't already been put on CDs by the Astronomical Data Center. So far, this has included:

    Disk 1:
          Files for the most recent versions of the General Catalogue of
          Variable Stars (GCVS), New  Suspected Variables (NSV),  and the New
          Suspected Variables Supplement (NSVS).
          Wolfgang Steinicke's files from the NGC-IC Project (
          Veron and Veron-Cetty's catalogues of quasars,  active galactic
          nuclei (AGN),  and BL Lacertae objects,  version 10.
          A dataset of stars with decent photometric accuracy,  compiled by
          Brian Skiff of Lowell Observatory for the LONEOS asteroid search
    Disk 2:
          Washington Double Star catalogue:  WDS-2001.
          Fifth Catalog of Orbits of Visual Binary Stars,  by William I.
          Hartkopf, Brian D. Mason, & Charles E. Worley,  of the USNO.
          Catalogue of Components of Double & Multiple Stars.  This has
          been processed to add explicit RA/dec data for stars that previously
          only had a separation and position angle from another star.  Also,
          data from the "Visual Double Stars in Hipparcos" catalog have been
          merged in.

    Be aware that some of these items were added more recently than others. If you have an older disk, you may find that only some of the above files are in place. Current disks will have all of them.

    Also: on the original disks, disk 1 contains GSC data from dec -7.5 degrees to the north celestial pole, and disk 2 contains data from dec -7.5 degrees down to the south celestial pole. There was no overlap. However, there was room on disk 2 to put data from dec 0 (celestial equator) down to the south celestial pole, allowing for 7.5 degrees of overlap. Some programs may find this helpful, since it will mean they can grab data without needing to swap CDs. (Unfortunately, most will assume use of "original" GSC 1.1 disks, and will still insist you swap disks.)

    What programs can make use of these disks? I know for a fact that the astrometric reduction programs Astrometrica and CCD Astrometry will be able to make use of these disks. Users of PinPoint and Charon need not worry about any of this; both programs can automatically convert GSC-1.1 positions to GSC-ACT, with no new disks needed. Users of Canopus also won't find these disks useful, because that program has its own pre-stored version of the GSC-1.1, in its own format.

    Also, Han Kleijn's freeware program Hallo Northern Sky and Patrick Chevalley's Cartes du Ciel can read these disks. More generally, I would expect that any program that says it can use the GSC-1.1 as supplied on CD-ROM by the Astronomical Society of the Pacific should be able to use these GSC-ACT disks instead.

    Can I make copies of these disks?: Yes.

    There was some question about this at first, because GSC-1.1 was copyrighted by AURA, the Association of Universities for Research in Astronomy. I asked several people at AURA and at the Space Telescope Science Institute why GSC-1.1 was under a copyright, and I never really got a straight answer. But I got the distinct impression that they just wanted some control over its use, so they could quash products such as, "Your love life as foretold by the Hubble Space Telescope's star catalog... Saturn is in conjunction with GSC 1234 5678; better just not get up today", or "Here's a star chart showing the star you registered with your name; GSC 1234 5678 will henceforth be officially known as Eddie". The Space Telescope folks had just had the mirror aberration embarrassment, and probably felt that they needed no new fiascoes.

    However, it appears that GSC-ACT does not fall under the same copyright. As far as I'm concerned, it is in the public domain, meaning that it can be used for all purposes, both commercial and non-commercial.

    Why you probably don't really want GSC-ACT: When GSC-1.0 and GSC-1.1 came out around 1990, they represented an incredible leap forward in star catalogues. GSC-ACT was (in my admittedly prejudiced opinion) a very nice improvement to a great dataset. But GSC has a fair number of false "stars", the positions are only good to an arcsecond or so (even after the GSC-ACT recalibration), the magnitudes are only rough estimates, and there is no proper motion data. In the last few years, at least three star catalogues have been released that offer more stars, more accurate positions and magnitudes, and fewer errors. If you can use any of them instead of GSC-ACT, I'd recommend doing so. The only reason I can think of to use GSC-ACT these days would be that your software doesn't support one of the following catalogs.

  • UCAC-3 contains about 100 million stars, roughly five times as many as GSC. It gives highly accurate positions, decent magnitudes, and even pretty good proper motion data. It essentially makes GSC-ACT completely and totally obsolete. If at all possible, I'd recommend getting UCAC-3 and using your GSC-ACT disks as Frisbees or drink coasters.
  • UCAC-3 can be received from USNO at no cost on a double-sided DVD. Click on the above link for details, both about the catalog and about how to get the DVD.

    The one possible roadblock to UCAC-3 use is that it's new (just came out in August 2009), and most software doesn't actually use it yet.

  • USNO-A2.0 is a true "mega-catalogue", covering about half a billion stars, about thirty times as many as GSC. The positions and magnitudes are about as good as those from GSC. The data comes from scanning in two photographic plates for each part of the sky. This helps avoid the sort of spurious stars found in GSC, because it's rare that the same mistake is going to occur on both plates. It also means that both a red and a blue magnitude got measured for each star. Unlike UCAC-2, the data covers the entire sky.
  • You can get A2.0 via my A2.0 pass-it-along scheme, on eleven CD-Rs or two DVD-Rs. At one time, USNO was distributing the eleven CD form at no charge, but they ran out of disks long ago.

  • USNO-B1.0 is the successor to A2.0. This time, USNO scanned in not just two, but five plates per area. That allowed them to get about twice as many stars, and to provide up to five magnitudes per star (two red magnitudes, two blue, and an infrared magnitude.) It also allowed proper motions to be added to the dataset, though I gather these are not of especially great quality.
  • Ideally, we'd all use B1.0 in place of A2.0. The problem is that B1.0 consumes about 80 GBytes (as opposed to 6.3 GBytes for A2.0). I've heard rumors that there's a gent in Europe who is distributing B1.0 on 80-GByte USB hard drives, but have no details on this.

  • Honorable mentions: There's now a GSC-2.2 catalogue, which rivals the size and detail of B1.0. But it's even harder to get than B1.0. There's also a new dataset, CMC-14, with 95 million stars and excellent positions and photometry. (None of the other datasets really took photometry seriously, and errors of up to a full magnitude are all too common.) But it only covers declinations -30 to +50, and was gathered using drift-scan methods. That means it would be hard to extend it to full-sky coverage. Also, it's so new that I don't think much software exists that makes use of it. Still, if you're doing asteroid photometry, most of your work will be in that -30 to +50 zone, and this catalogue deserves a look.
  • Price list: I'm basically charging the cost of burning CD-Rs and of postage. This works out, roughly, to about $1 per CD-R (and GSC-ACT consumes two disks, so I'm charging $2/set.) Shipping this in the US and Canada costs about $3; outside these countries, about $5. Thus, the "usual order" of a single copy of GSC-ACT will cost a total of $5 for a US or Canadian customer, $7 for anyone else.