GAVO at AG-Tagung 2017, Göttingen

[Image: Booth 2017]

For the 11th time, GAVO has a booth at a meeting of the venerable Astronomische Gesellschaft (AG). This year, we are in Göttingen, again offering advice to users and data providers at our booth (if you’re looking for us: We’re close to the entrance of Hörsaal 5).

And again we have a Puzzler, a little problem easily solved if you know your VO tech – and if you don’t we’ll gladly help you at our booth. We are also giving hints there, one being released at each coffee break on Tuesday and Wednesday (there are little posters with them, too, if you miss one). Of course, if you’re not in Göttingen, you’re still welcome to try your hand. You won’t get to win our great first prize then, the big Crab Nebula towel (it should be easy to spot on the image above).

If, on the other hand, you are in Göttingen, be sure to drop by our splinter meeting. Yours truly, for instance, will speak about EPN-TAP (remember And the Solar System, too right here? That’s what this is about).

Update 2017-09-20, 17:00 We’ve just given out the last hint for the puzzler, and so we can publish them all over on the puzzler archive: Hints for the 2017 puzzler. If you’re in Göttingen, you still have until tomorrow 16:00 to hand in a solution and perhaps win our nice and fuzzy Crab Nebula towel.

Update 2017-09-21, 17:00 And the winner is… again not from Marburg, which is beginning to become a running gag, and they’ve been unlucky for the last three years in a row. Anyway, here’s our proposed solution.

The Earth is Our Telescope

Antares 2007-2012 neutrino coverage
The coverage of the 2007-2012 Antares neutrinos, with positional uncertainties scaled by three.

At our Heidelberg data center, we have have already published some neutrino data, for instance the Amanda-II neutrino candiates, the IceCube-40 neutrino candidates, and the 2007-2010 Antares results.

That latter project has now given us updated data, for the first time including timestamps, available as the Antares service.

Now, if you look at the coverage (above), you’ll notice at least two things: For one, there’s no data around the north pole. That’s because the instrument sits beyond the waters of the Mediterranean sea, not far from where some of you may now enjoy your vacation. And it is using the Earth as its filter – it’s measuring particles as they come ”up” and discards anything that goes “down”. Yes, neutrinos are strange beasts.

The second somewhat unusual thing is that the positional uncertainties are huge compared to what we’re used to from optical catalogs: a degree is not uncommon (we’ve scaled the error circles by a factor of 3 in the image above, though). And that requires some extra care when working with the data.

In our table, we have a column origin_est that actually contains circles. Hence, to find images of the “strongest” neutrinos in our obscore table, you could write:

SELECT * FROM
ivoa.obscore AS o
JOIN (
  SELECT top 10 * FROM antares.data
  ORDER BY n_hits desc
) AS n
ON 1=INTERSECTS(
  s_region,
  origin_est)

in a query to our TAP service.

But of course, this only gets really exciting when you can hope that perhaps that neutrino was emitted by some violent event that may have been observed serendipitously by someone else. That query then is (and we’re using all the neutrinos now):

SELECT * FROM
ivoa.obscore AS o
JOIN antares.data as n
ON  
   epoch_mjd between t_min-0.01 and t_max+0.01
  AND
    dataproduct_type='image'
  AND
    1=INTERSECTS(origin_est, s_region)

On our data center, this doesn’t yield anything at the moment (it does, though, if you do away with the spatial constraint, which frankly suprised me a bit). But then if you went and ran this query against obscore services of active observatories? And perhaps had your computer try and figure out whether anything unusual is seen on whatever you find?

We think that would be really nifty, and right after we’ve published a first version of our little pyVO course (which is a bit on the back burner, but watch this space), we’ll probably work that out as a proper pyVO use case.

And meanwhile: In case you’ll be standing on the shores of the Mediterranean this summer, enjoy the view and think of the monster deep down in there waiting for neutrinos to detect – and eventually drop into our data center.

DaCHS 1.0 released

Today, I have released DaCHS 1.0 – after long years in the 0.9 range, it was finally time to do so. The jump in the major version number was an opportunity to remove some cruft that had accumulated over the years; this, on the other hand, means that if you’re running DaCHS, you should watch the upgrade and see if anything broke later (this might be the perfect time to add regression tests to your RDs).

The changelog is below, but before that a bold-faced warning:

Install python-astropy before upgrading

This is because DaCHS now depends on astropy rather than pyfits and pywcs. The latter is no longer part of Debian stretch, and so we made the jump to astropy (that would have been due during Debian stretch’s lifetime anyway) even before 1.0.

Now, Debian holds back packages with new dependencies, and due to the way DaCHS’ modules are distributed, DaCHS will break when some of its packages are held back. The symptom is error messages like “pkg_resources.DistributionNotFound: gavodachs==0.9.8”. If you already see those, a apt-get dist-upgrade should get you in business again.

With this out of the way, here is an annotated log of the major changes:

  • DaCHS’ main entry point is now actually called dachs (i.e., call dachs imp q and such in the future). gavo will work as an alias for quite a while to come, though, and it’s still used a lot in the documentation (you’re welcome to fix this: the docs are maintained on github).
  • Hopefully more useful manpage (of course, also available with man dachs) – have a peek!
  • UWS support is now at version 1.1 (i.e., there’s creationDate in jobs, filters in the joblist, and slow polling).
  • Added “declarative” licenses. Please read the Licensing chapter in the tutorial and slap licenses on your data.
  • Now using astropy.wcs instead of pywcs, and astropy.io.fits instead of pyfits. The respective APIs have, unfortunately, changed quite a bit. If you’re using them (e.g., in processors), you’ll have to change your code; it’s unlikely services are impacted at runtime. (see also How do I update my code?).
  • Removed the //epntap#table-2_0mixin. Use
    //epntap2#table-2_0 instead (sorry).
  • Removed sdmCore (use Datalink/SODA instead); the SODA procs in //datalink are also gone, use the ones from //soda instead (sorry, SODA development has been difficult on the IVOA level).
  • Removed imp -u flag and the corresponding updateMode parse option. If you used that or the uploadCore, just mark the DDs involved with updating="True" instead.
  • Massive sanitation of input parameter processing. If you’ve been using inputTable, inputDD, or have been doing creative things with inputKeys, please check the respective services carefully after upgrading. See also DaCHS’ Service Interface in the reference documentation. The most user-visible change in this department is if you’ve been using repeated parameters to fill array-valued inputs. That’s no longer allowed; if you actually must have this kind of thing, you’ll need a custom core and must fill the arrays by hand.
  • In DaCHS’ SQL interface, tuples now are matched to records and lists to arrays (it was the other way round before). If while importing you manually created tuples to fill to array-like columns, you’ll have to make lists from these now.
  • rsc.makeData or rsc.TableForDef no longer automatically make connections when used on database tables. You must give them explicit connection arguments now (with base.getTableConn() as conn:).
  • logo_tiny.png and logo_big.png are now ignored by DaCHS, all logos spit out by it are now based on logo_medium.png, including, if not overridden, the favicon (that you will now get if you have not set it before).
  • Removed (probably largely unused) features editCore, SDM2 support, pkg_resource overrides, simpleView, computedCore.
  • Removed the argparse module shipped with DaCHS. This breaks compatibility with python 2.6 (although you can still run DaCHS with a manually installed argparse.py in 2.6).

Even though that’s quite a mouthful, I expect few people will actually experience breaking services. If you do, by all means let us know on the DaCHS-support mailing list.

As usual, the general upgrading instructions are available in the operator’s guide; if you plan on upgrading to stretch soon, also have a look at hints on postgres upgrades. Stretch comes with postgres 9.6 (jessie: 9.4), and you should migrate sooner or later anyway.

Users not using Debian’s package management can, as usual, grab tarballs from http://soft.g-vo.org/dachs.

ADQL tricks at MPIA

Aerial image of Heidelberg and Königstuhl
The 2017-06-29 ADQL talk (red circle) from 30000 ft

Today I was up on Heidelberg’s signature mountain, Königstuhl, at the Max-Planck-Institute for Astronomy for a little talk on what I’d provisionally call “intermediate ADQL” – discussing some aspects of ADQL and some TAP techniques that may not be immediately obvious but still generally and straightforwardly applicable to everyday problems. Since I suspect the lecture notes for that talk may be of interest to some readers of this blog, I thought I should share them here.

What this also contains is a very quick piece of pyVO-based python (which needs both this helper and a recent pyVO) for a use case that comes up fairly often: “Give me all proper motions (radio fluxes, distances, radial velocities, whatever) for object in this region.”

This uses a discovery case I’ve been after for quite a while now: Find services by the UCDs of tables within them. And while that’s been possible for quite a while on GAVO’s Registry UI WIRR, there’s still too many services that don’t declare their tables to the Registry, and when talking about TAP, the situation is still a bit worse (as has been mentioned in my account of the last interop). So – enjoy the code, but very frankly, you’ll still see wires sticking out for a several months yet.

And if you run a TAP service yourself, please have a look at how to enable table discovery over on the IVOA wiki so we can finally get those pesky wires out of our users’ eyes.

GAVO at the Northern Spring Interop

[IVOA 2002-2017]
15 Years of IVOA: The birthday cake our Shanghai hosts prepared for us.

Every half year, VO enthusiasts from all over the world gather for an “Interoperability conference”, or Interop for short. The latest such event, the Shanghai Interop 2017, ended Friday a week ago. It has been a “long” one again after the short southern spring Interop in Trieste last year (featured in this blog).

As usual, it was a week of many discussions and much consensus-building. In this post, I’d like to mention a few of the GAVO-related contributions; links typcially go to slides or lecture notes PDFs.

On the Registry side of things, we’re currently (among many other things) briding the gap between DOIs and the Registry in VOResource 1.1, and we invited registry providers to take up the new features, as well as proposing how to update RegTAP (which is used to actually query the Registry) to cope with the new metadata.

Also in Registry, our efforts of almost a decade to properly support registering tables and similar data collections bore fruit (Britain’s Mark Taylor reported on his experiences taking up our current proposal), and the fairly spectacular new Aladin V10 (presented by the CDS’ Pierre Fernique, who showed off what I’m tempted to call a “visual registry interface”) urgently needs what we’ve developed over the years.

We furthermore reported on new steps to finally let people search the registry using Space-Time constraints (spoiler: the tech is almost there, registry records need lots of work).

Spatial searches in the registries are one thing enabled by storing and searching for MOCs in relational databases, as was reported by Markus Nullmeier over in an Applications session. The setting may already tell you that these MOCs (Multi Order Coverages, a healpix-based way of representing fairly arbitrary areas on the sky) have applications far beyond Registry.

Also in Apps, Ole reported on progress in packaging VO applications for easy and reliable installation, in this case for Debian and derivatives. Finally for Apps, Margarida reported on getting lines and line lists into the spectral analysis package SPLAT: Implementation of SLAP and VAMDC interfaces in SPLAT-VO.

In the wider area of data access protocols and underlying data models, we contributed to Marco’s talk on the long-overdue facelifting for the VO’s bedrock, Simple Cone Search (Keeping SCS up-to-date within DAL landscape) – the fact that there’s an installed base of 15000 of such services may let you guess that we need to tread lightly here. On the bleeding-edge side of things, we presented our current ideas on how, eventually, several data models, data modelling as such and the annotation of data according to these data models might play together in publishing time domain data with DACHS (previously featured on this blog in a slightly less technical way).

We also talked about education and outreach. Hendrik reported on our ADQL course and how it helps future astronomers learn dealing efficiently with even very large datasets. Hendrik’s long-lasting dedication to these topics did not go unpunished at this interop: since the Exec meeting on the Interop Wednesday he is vice-chairing the education interest group of the IVOA. Back in the session I also mused a bit about what metadata changes are needed to make the VO tutorial collection VOTT more useful.

It is a particular pleasure for me to mention that the IVOA has a new interest group: “Solar System”. Regular readers of the blog will have noticed that I have a particularly soft spot in my heart for that crowd, and so I gave a short overview over how DaCHS is used among them, too.

And that’s just the official programme. Much more fixing, designing, and discussion went on between sessions or in the evenings. The latter, of course, included some decidedly less technical aspects. Including, as pictured above, a nice birthday cake for the IVOA, as it is now 15 year since the first Interop meeting in January 2002.

Time Series

The IOVA’s committee on science priorities (CSP) has declared the “time domain” as one of its focus topics quite a while ago, an action boiling down to a call to the IVOA member projects to think about support for time series and their analysis in services, standards, and clients.

While for several years, response has been lackluster, work on time series has gathered quite a bit of steam recently. For instance, the spectral client SPLAT (co-maintained by GAVO) has grown some preliminary support to properly display time series (very rudimentary in what’s currently released), and lively discussions on proper metadata for time series have been going on on the Data Models mailing list of the IVOA – if you’re interested in the time domain, this would be a good time to subscribe for a while and comment as appropriate.

Meanwhile, in our Heidelberg data center, we’ve joined the fray by publishing our first time series service (science background: searching for exoplanets in the Milky Way bulge using gravitational lensing), which is available through SSA (look for k2c9vst) and through ObsCore (at http://dc.g-vo.org/tap, collection name k2c9vst), too. For details see also the service info.

Since right now future standards are being worked out, this is a perfect time to publish your time series; this way you get to influence what people will be able to tell machines about their time series in the next couple of years. Ask our staff (contact below) if you want us to publish for you. But you can also self-publish using the DaCHS publication package. Refer to the resource descriptor of the k2c9vst service to get started.

At its heart is the table definition of the time series, which is basically


<table id="instance">
  <column name="hjd" type="double precision"
      unit="d" ucd="time.epoch"
      tablehead="Time"
      description="Time this photometry corresponds to."
      verbLevel="1"/>
  <column name="df" type="double precision"
      unit="adu" ucd="phot.flux"
      tablehead="Diff. Flux"
      description="Difference as defined by 2008MNRAS.386L..77B"
      verbLevel="1"/>
  <column name="e_df"
      unit="adu" ucd="stat.error;phot.flux"
      tablehead="Err. DF"
      description="Error in difference flux."
      verbLevel="15"/>
</table>

– in the actual service, there are a few more columns, but time, value, and error actually make up a full time series.

Except that a machine can’t really tell what this is yet (well, perhaps it could using UCDs, but that’s a different matter). What it needs to work out is what’s the independent axis, what the frames are, etc. And to do that, the machine needs annotation, i.e., machine-readable, structured declarations alongside the data and the “classic” metadata like units and descriptions.

In actual VOTables, this will be happening through VO-DML annotation, which is also still seriously being discussed; whatever we currently spit out you can inspect in the XML source of this example document.

DaCHS, however, isolates you from the concrete details of writing VOTables. Instead, you write annotations in a JSON-inspired little language we’ve christened SIL (“Simple Instance Language”; reference). The complicated part is to know what types and attributes you have to declare, which is exactly what the data models is a bout. As said initially, the details are still in flux here, but this is what things look like right now:


<dm>
  (ivoa:Measurement) {
    value: @df
    statError: @e_df
  }
</dm>

<dm>
  (stc2:Coords) {
    time: (stc2:Coord) {
      frame:
        (stc2:TimeFrame) {
          timescale: UTC
          refPosition: BARYCENTER 
          kind: JD }
      loc: @hjd
    }
    space: 
      (stc2:Coord) {
        frame:
          (stc2:SpaceFrame) {
            orientation: ICRS
            epoch: "J2000.0"
          }
        loc: [@raj2000 @dej2000]
    }
  }
</dm>

<dm>
  (ndcube:Cube) {
    independent_axes: [@hjd]
    dependent_axes: [@df @mag]
  }
</dm>

If you consider this for a moment, you’ll see that each dm element corresponds to something like an object template of a certain “type”. The first, for instance, defines a measurement with a value and a statistical error. Both happen to be given as references to columns in the table defined above (as indicated by the @ signs).

The last annotation defines a data cube; a time series in this definition is simply a data cube with just a single non-degenerate independently varying axis (the independent_axis attribute; in the value the square brackets indicate a sequence) that happens to be time-like. And that hjd is time-like, VO-DML enabled clients will work out when interpreting the STC (“Space-Time-Coordinates”) annotation. In there, you will see that hjd is referenced from the time attribute and with a time-like frame that also defines that this particular flavor of HJD is what a hypothetical clock at the solar system’s barycenter would measure if it stood in the gravitational potential in Greenwhich, and had leap seconds thrown in now and then. And that long story is communicated through “literals”, constant strings like “BARYCENTER” or ”TT”, which are also legal within DaCHS data model annotations.

This may seem a bit complicated at first. I argue, though, that given what time series clients will have to do anyway, going through the cube and STC annotations is actually about the most straightforward thing you can do.

But perhaps I’m wrong, so again: None of this is cast in stone right now. Comments are even more welcome than usual, either below or at gavo@ari.uni-heidelberg.de.

Asterics Tech Forum

The 3. Asterics DADI Tech Forum took place last week in Strasbourg – and many GAVO members made contributions as well.
This time, there were 3 slots for hackathon sessions, which were also used for discussions. We’ll mention two highlights of our contributions here.

We took the opportunity to push our Provenance Data Model efforts and used the hackathon slots for provenance discussions.
One topic was the links between the simulation data model and ProvenanceDM, and how to map from SimDM to ProvenanceDM classes. This mapping works quite well and will be included in the working draft for the data model. We also had an interesting talk by José Enrique Ruiz on his view on Provenance, workflows, and – very important – the “deployer” and “system” provenance for storing all the environment variables that may be needed to rerun the processing of some observational data. Michèle Sanguillon also presented for the first time her extension to the prov Python library (W3C) with extensions from our IVOA Provenance Data Model. We also had interested people from outside the usual provenance-interested people joining in, e.g. from the Astron project. More about our Provenance modelling efforts can be found at IVOA Provenance wiki page.

A world premiere (of sorts) was the first discussion of RegTAP 1.1. RegTAP is a search interface to the VO Registry; it is what TOPCAT or other VO clients uses when you type in keywords to locate services. A fairly direct web-basd interface is our WIRR registry interface. RegTAP will need a bit of a makeover since VOResource, the underlying metadata scheme is currently receiving one, allowing, in particular, for including DOIs and ORCIDs (John Does of this world, rejoice: People can finally uniquely find your data and not that of all the other J. Does) in Registry records and figuring out licenses on data. Licensing may not matter when you use data in a paper but it does matter if you want to redistribute data, e.g. for planetarium programs with catalog data or pretty pictures, or when re-mixing data.

But of course the GAVOistas happily joined the fray on the many other topics discussed, from a standard format for a time series to interoperable authentication, from datalink applications to figuring out if data coming into a program should be treated as a collection of spectra or rather an object catalog – the latter in the context of the upcoming version 10 of the VO’s premier image tool Aladin, which we saw (probably another premiere) demoed. We can already promise you an exciting update!

And the Solar System, too

Virtual Observatory technologies are increasingly being adopted outside of “core” astronomy in the vicinity of the optical band (to which they have had, I’ll have to admit, a certain slant) . An excellent example for that trend is the Europlanet community. Their goal is to make solar system data accessible without fiddling, and they are employing a wide range of VO standards for that. At the heart of their efforts are TAP and the VO Registry.

While the usual VO client software will of course work fine with their services, they are offering a nice web-based discovery tool executing queries against an increasing number of services. Such uniform quering over many services is possible is because all of them implement TAP and host EPNcore tables. The resulting interface, also known as EPN-TAP, allows for very flexible discovery and retrieval of solar system data products, much like ObsTAP does for astronomical observations outside of the solar system.

Since quite a few EPN-TAP services are built using GAVO’s DaCHS publication suite, I was invited to this week’s VESPA implementation workshop 2017 in Graz to help the data providers set up their services.

I can’t deny that I’m somewhat excited when I see how our software is used to publish spectra of the ice blocks in Saturn’s ring taken by the lonely Cassini spacecraft still orbiting the gas giant, or data transmitted by Rosetta, now (and for who knows how long) sitting on comet 67P/Churyumov-Gerasimenko. There’s even an upcoming archive of solar system alerts that may, according to its builders, include events like meteor showers on Mars. I can almost hear my code whisper “I’ve archived signals of C-beams glitter in the dark near the Tannhäuser Gate”.

Even documentation can become otherworldly in this business: Already in February, DaCHS has learnt to procude GeoJSON, a format common in the GIS community and also adopted by Europlanet – planetology has lots of common ground with geoinformatics. And in the reference documentation on annotating tables to enable that, when I wrote “standards-compliant GeoJSON clients will interpret your coordinates as WGS84 on Earth if you leave [frame annotation] out”, I was severely tempted to add “which is probably not what you want” and feel like Spaceman Spiff.

Romantic space adventures aside, after this intense week, not only are there several additional or improved EPN-TAP services from places ranging from Pasadena to Villafranca to Warsaw in the pipeline, the close interaction with the data providers has also led to very significant improvements to DaCHS’ EPN-TAP support. The tutorial chapter on EPN-TAP and the reference documentation linked from there already reflect the results of this workshop. You’ll need a current DaCHS beta package for that to work, though; we expect this stuff to go into our release packages around July.

If any of the workshop participants read this: Thanks a lot for your patience with DaCHS’ sometimes somewhat cryptic diagnostics. If, on the other hand, you missed the Graz workshop and have solar system data: Please talk to us or the kind and friendly Europlanet folks – either us will be delighted to support your publication project. And perhaps we’ll meet you at the next such workshop, planned for 2018 in the Czech Republic.

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
FROM TAP_UPLOAD.t1
LEFT OUTER JOIN ident
ON (id=normId(col1))
LEFT OUTER JOIN basic
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://edu.gavo.org/hd/gavo_addpms). 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.

See Who’s Kinking the Sky

A new arrival in the GAVO Data Center is UCAC5, another example of a slew of new catalogs combining pre-existing astrometry with Gaia DR1, just like the HSOY catalog we’ve featured here a couple of weeks back.

That’s a nice opportunity to show how to use ADQL’s JOIN operator for something else than the well-known CONTAINS-type crossmatch. Since both UCAC5 and HSOY reference Gaia DR1, both have, for each object, a notion which element of the Gaia source catalog they correspond to. For HSOY, that’s the gaia_id column, in UCAC5, it’s just source_id. Hence, to compare results from both efforts, all you have to do is to join on source_id=gaia_id (you can save yourself the explicit table references here because the column names are unique to each table.

So, if you want to compare proper motions, all you need to do is to point your favourite TAP client’s interface to http://dc.g-vo.org/tap and run

SELECT 
    in_unit(avg(uc.pmra-hsoy.pmra), 'mas/yr') AS pmradiff, 
    in_unit(avg(uc.pmde-hsoy.pmde), 'mas/yr') AS pmdediff, 
    count(*) as n, 
    ivo_healpix_index (6, raj2000, dej2000) AS hpx 
    FROM hsoy.main AS hsoy 
    JOIN ucac5.main as uc 
    ON (uc.source_id=hsoy.gaia_id) 
    WHERE comp IS NULL    -- hsoy junk filter
    AND clone IS NULL     -- again, hsoy junk filter
    GROUP BY hpx

(see Taylor et al’s All of the Sky if you’re unsure what do make of the healpix/GROUP BY magic).

Of course, the fact that both tables are in the same service helps, but with a bit of upload magic you could do about the same analysis across TAP services.

Just so there’s a colourful image in this post, too, here’s what this query shows for the differences in proper motion in RA:

(equatorial coordinates, and the aux axis is a bit cropped here; try for yourself to see how things look for PM in declination or when plotted in galactic coordinates).

What does this image mean? Well, it means that probably both UCAC5 and HSOY would still putt kinks into the sky if you wait long enough.

In the brightest and darkest points, if you waited 250 years, the coordinate system induced by each catalog on the sky would be off by 1 arcsec with respect to the other (on a sphere, that means there’s kinks somewhere). It may seem amazing that there’s agreement to at least this level between the two catalogs – mind you, 1 arcsec is still more than 100 times smaller than you could see by eye; you’d have to go back to the Mesolithic age to have the slightest chance of spotting the disagreement without serious optical aids. But when Gaia DR2 will come around (hopefully around April 2018), our sky will be more stable even than that.

Of course, both UCAC5 and HSOY are, indirectly, standing on the shoulders of the same giant, namely Hipparcos and Tycho, so the agreement may be less surprising, and we strongly suspect that a similar image will look a whole lot less pleasant when Gaia has straightened out the sky, in particular towards weaker stars.

But still: do you want to bet if UCAC5 or HSOY will turn out to be closer to a non-kinking sky? Let us know. Qualifications („For bright stars…”) are allowed.