Posts with the Tag Tutorials:

  • Updates to GAVO's Tutorials

    Over the years, GAVO has produced a number of VO tutorials, i.e., texts that introduce some technique related to using the Virtual Observatory, preferably within some halfway plausible scenario. In effect, they are software documentation, and as software itself, software documentation suffers from bit rot. To work against that, the tutorials have to be revised occasionally.

    My two student assistants Sonja Gabriel and Chuanming Mao have recently done some of that revising. Let me use this opportunity to show off some of these freshly polished tutorials.

    A classic one (that has, if I may say so myself, aged rather well), is Adding catalog data to object lists using the VO. This is a thinly disguised introduction to TAP uploads, arguably the most powerful of all the VO tech to date. If you have come to this place without ever having done a TAP upload, you owe it to yourself to at least skim the tutorial and quickly follow along the few steps to do positional crossmatches with just about any astronomical catalog and with just about any level of sophistication.

    part of a screenshot: a histogram, a sky photo with overplotted points

    Another classic – it has its roots in the original Italian VO Days[1] – is TOPCAT and Aladin working together. It is using SDSS data of some galaxy cluster to try and get you to to send around data and positions between different programs using SAMP. If you are reading VO blogs, it is not unlikely this kind of thing will make you yawn. But at VO Days, it's little things like this that usually most immediately appeal to students and researchers alike.

    part of a screenshot: a color-magnitude diagram is a very narrow main sequence, and a proper motion plot

    From a tech point of view, Explore the Pleiades with TOPCAT and Aladin also mainly looks at SAMP (perhaps even somewhat less convincingly), but it's such a striking demo of what an amazing instrument Gaia is, and it's a nice introduction to TOPCAT's VO interface and subsetting facility that it's definitely worth a look, in particular as a showcase of having instant results with the VO.

    circular cloud of red crosses and blue circles in a celestial coordinate system

    An entirely different topic (well: it also employs SAMP for a moment) is covered by Data Discovery Using the Virtual Observatory Registry. This is trying to motivate looking for data collections in the VO Registry (in the form of our Browser interface to it). This tutorial has grown quite a bit during the review and now includes two sections joining data from different resources for various purposes. One section illustrates how systematics of quasar redshifts might be looked into using different sources, the other investigates the Tully-Fisher relationship in different spectral bands.

    A TOPCAT-plotted histogram with a sharp peak around 39.5 AU and a much wider one around 44.

    The tutorial on Asteroids in the Solar System was entriely overhauled. It was (and still is) mainly intended to be used in schools, and thus it originally just built on things that ran in a web browser. As is typical of things in web browsers, they have long since vanished. Hence, a rather fundamental update was necessary anyway. While we were looking for interesting things to do – the plot above, by the way, is the distribution of major halfaxes in the Kuiper belt –, we ended up even includeding a brief bit on ADQL.

    Due to its school focus, we are also offering this particular text in German as well as in English. If you are an Astronomy teacher with particularly motivated pupils , we would like to hear from you…

    An aladin window showing two aligned photos of the ring nebula in Lyra

    The last revised tutorial I would like to mention also has a somewhat special (main) target audience: Astrometric Calibration using Aladin. Admittedly, automatic, or “blind” calibration has become really great, and I think getting their images located on the sky is not much of a problem even for amateurs any more, thanks in part to services like But then – sometimes there is nothing like a good, old manual, ummm, “plate” solution. Aladin and the VO make that lot less tedious than it used to be.

    Of course, I cannot have a post on tutorials without mentioning the VO Text Treasures, a web page that shows the educational material currently registered in the VO Registry. This little page also accounts for bit rot: You can sort by the time last inspected there, and thanks to Sonja's and Chuanming's efforts, our tutorials look very good in that representation at the moment.

    In case you have some material suitable for WIRR yourself: Please register it, too. Send me a mail and I will lend you a hand (or, if you are a VO pro, directly read the pertinent standard).

    [1]That's block courses on VO matters lasting a day or two. If you are in Germany, you can book us for your very own one!
  • From Byurakan to L2: Short Spectra

    A snapshot from the DFBS tutorial: Carbon Stars in different spectral bands.

    A snapshot from the DFBS tutorial: Carbon Stars in different spectral bands.

    On June 30, a small project we've done together with the Armenian Virtual Observatory has ended. Its objective was to publish the spectra from the First Byurakan Survey (the DFBS) in a VO-compilant way. The data comes from one of the big surveys with Schmidt telescopes that form a sizable part of the observational heritage from the second part of the 20th century (you're still using a few of them daily if you tell Aladin to show a DSS plane).

    In this case, spectra from objects on the entire northern sky off the milky way down to about 18th mag were obtained. In a previous cooperation between Armenian and Italian astronomers a good decade ago, the plates were digitised and calibrated, and spectra were extracted. However, they resided behind a web interface so far, which made them somewhat clumsy to work with.

    Now, they're in the VO, and to give you a few ideas for what kind of things you can do with this kind of data, within the project we've also written the tutorial “Outlier Analysis in Low-Resolution Spectra”.

    Have a glance at the tutorial – you see, while the Byurakan survey certainly is a valuable resource by itself, I happen to believe at this point it's particularly valuable because with the next Gaia data release (planned for next year), a deluxe version of it will come: Gaia's RP/BP spectra will be all-sky, properly calibrated, and quite a bit deeper, but still low-resolution. So, if you're just waiting for such a data collection, you can train your methods right now on the DFBS.

  • Small Telescopes, Large Surveys

    Image: Blink comparator and survey camera

    Plate technology at Bamberg observatory: a blink comparator with one plate mounted, and a survey camera that was once used at Boyden Station, an astronomer outpost in 60ies South Africa.

    I'm currently at the workshop “Large surveys with small telescopes: past, present, and future” (or Astroplate III for short) in Bamberg, where people are discussing using and re-using the rich heritage of historical observations (hence the “plate” part) as well growing that heritage in the age of large CCDs, fast computers and large disks.

    Using and re-using is of course what the Virtual Observatory is about, and we've been keeping fairly large plate collections in our data center for quite a while (among them the Archives of Landessternwarte Königstuhl or the Palomar-Leiden Trojan surveys, and there is the WFPDB TAP-accessibly). Therefore, people from GAVO Heidelberg have been to all past astroplate conferences.

    For this one, I brought a brand-new tutorial on plate scans in the VO, which, I hope, also works as a general introduction to image discovery in the VO using SIAP, Datalink, and Obscore. If you're doing image stuff now and then, please have a quick look at the thing – I am particularly grateful for hints on what to improve or perhaps particularly obvious use cases for the material discussed.

    Such VO proselytising aside, the conference is discussing the wide variety of creative, low-cost data collectors out there as well as computer-aided re-analysis extracting new knowledge from decades-old data. If I had to choose a single come-to-think-of-it moment, it would be Norbert Zacharias' observation that if you have a well-behaved object and you'd like to know where it was in 1900, it's now more accurate to extrapolate Gaia astrometry to the epoch of observation than to measure it on the plate itself. Which is saying a lot about the amazing feat of engineering that Gaia is.

    This is not, however, an argument for dumping the old data. Usually, it is exactly what is not so well-behaved (like those) that's interesting – both in terms of astrometry and in terms of photometry (for which there's a lot more unruly behaviour in the first place). To figure out how objects don't behave well, and, for objects disguising as well-behaved only on time scales of the (say) Gaia mission, which these are, the key is “old” data. The freshness of which we're discussing this week.

  • Updated Proper Motion Tutorial

    At the risk of turning this into a blog on nice TAP tricks (which it's not supposed to be): Our classic short tutorial on adding proper motions to almost arbitrary object lists has just gotten a facelift today.

    And there's new content, too – I now show what to do when you don't even have positions but just object names. In order to keep this sufficiently geeky, here's the query as a spoiler:

    SELECT col1, ra, dec
    ON (id=normId(col1))
    ON (oidref=oid)

    But to close on a non-TAP topic: Registry! There's an experimental facility to have this kind of thing in the Registry; the PM tutorial is in, for instance, with the ivoid ivo:// One thing you can do with this is generate a list of registred documents that essentially updates itself from the registry.

    Another is figure out where the source code of the document is (if the authors choose to share it, which is of course a very smart thing to do); in our example it's in Volute, the IVOA's semi-official version control system. So, if you find a bug (defined as “superset of typo”) in the linked document, you're most welcome to supply patches as diffs or just directly fix things if you have commit privileges in Volute.

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