ephemeris, sampling

I fielded email today from various undergrads to whom I pitched (on Wednesday) a big project to build a precise probabilistic ephemeris for the Solar System. I am hoping to execute a huge project with a team of undergrads handling all the important parts.

At group meeting (before lunch), Iain Murray (Toronto, Edinburgh), who is one of our Bayesian consultants, gave a talk on sampling for inference, reviewing a few simple methods and then some hard pitfalls. A bit of an argument broke out about how you deal with well-separated maxima, with Roweis and me more on the side of "you never know if you have found the true maximum so you have to figure out how to do science without knowing that" and Scoccimarro and Blanton more on the side of "you have to keep working until you are sure".

history of cosmology

Jim Peebles (Princeton) visited today. Roweis and I spent an hour or so advertising to him our data analysis projects. Late in the day he gave a talk on the history of cosmology, which made a number of remarkable points, like that Hoyle was (almost) the first person to identify the cosmic microwave background (despite the fact that he thought it was impossible). An argument broke out about the importance of Friedman; Peebles takes the (tough) view that to be really important in cosmology you must have not just done theory but connected it directly to experiment, or not just done experiment but had the theorists realize that it was relevant. That's a high bar.

eccentricities

Zolotov and I worked on estimating eccentricities for stars in N-body simulations. This is not trivial—not even well defined—because there is no overall, unique potential (let alone a spherical one!).

sampling and Gaia

I spoke with Bovy about the possibility of doing an ambitious analysis of what is possible with Gaia. I spoke with Iain Murray (Edinburgh), who is visiting, about sampling, where he is one of the world's experts. I asked him to tell me what we can do if likelihood calls are outrageously expensive (so converged samplings of the posterior PDF are impossible).

out sick

I was on vacation on Friday and out sick today. That's not research.

grant proposal and infrared emission

Today was devoted to an NSF proposal, which, according to the rules, is not research. The only research activity of the day was a talk by Nadia Zakamska (IAS) about infrared emission lines and what they have to say about the physics of galaxies. She has some beautiful results, especially that the PAH emission and the H₂ emission in the interstellar medium are differently affected by dust extinction. This is odd, because they are both strongly correlated with star formation and one another. So they are strongly correlated but not co-spatial. Odd.

Comet Holmes

Lang and I worked on (that is, pair coded) making figures for our somewhat strange Comet Holmes project. We started by re-running everything from scratch (find images on web, download, source extract, calibrate) and made this, one of several images of the individual-image footprints on the sky. In this image, the brighter footprints are the more constraining footprints; axis units are degrees on the sky from some reference point.

fractals

My only research time today was spent fielding email about fractal universes, emails that were inspired by my arXiv submission yesterday. It turns out—contrary to what I wrote in that note—that there have been some serious attempts to compute observables in inhomogeneous models. I think my conclusions are still safe, but my language might have been a bit strong.

Roger Blandford

I spent all day today at the meeting in honor of Roger Blandford, which I played an embarrassingly microscopic effort in organizing. The meeting was incredibly well attended, with many old friends in attendance from all over the world. There were talks across the whole electromagnetic spectrum and covering a large range of astrophysical processes, all of which I enjoyed. In particular, Maxim Lyutikov (Purdue) gave just about the perfect description of Blandford the advisor (Lyutikov and I are coeval). Chris Kochanek (OSU) described a brute-force generative modeling of microlensing light curves that made my Bayesian heart sing. I spoke about model selection in cosmology, in a general way; I put my remarks on the arXiv here.

modeling galaxies with galaxies

I spent a long time on the phone with Lang, who is building quantitative models of galaxy images using other galaxy images. We spoke about the free parameters, and the robustness of the fitting (given that there are some random superimposed stars and the like), and so on. He has some nice results already, and this has only been underway for a few days now. At the end of the day I gave a big public talk here in Buffalo.

Buffalo

I worked on two talks for Buffalo and one for Stanford today; I also gave one of the Buffalo talks.

averaging data

I spoke with Schiminovich about what we can achieve by taking first moments (means) of low signal-to-noise data. There is quite a bit you can do (I think), though we haven't worked out all the details. This all relates to our hope of constraining properties of quasars and the Universe with low signal-to-noise GALEX observations.

The WWW is a sky survey

One of the things I have been saying for a few years is that the astronomical images available on the Web, taken together, form some kind of very heterogeneous and odd sky survey. Could this be used to do science? Lang and I have an argument that it can: He Web-searched "comet holmes", took all images found that way, calibrated them with Astrometry.net (many didn't calibrate because, for example, they were images of cats or grandmothers), and fit a gravitational trajectory in the Solar System to the image locations. We started to write this up today.

done and done

Astrometry.net paper up on arXiv today; noise-information paper going up tomorrow. My research today was just finishing tweaks on the latter.

arXiv issues

I spent most of the day chatting, notably with Stumm, who is in NYC for a few days. Late in the day, Lang (attempted to) put the Astrometry.net paper up on the arXiv. This was a failure, and not for the usual reasons: None of the figures got flagged as too big!

The paper compiles without complaint by "pdflatex astrometry-dot-net" on any unix (mac or Linux) platform we have been able to try. And yet on arXiv, the figures can't be understood! (It can't determine size or bounding box or format or even see the file in some cases.)

The arXiv system has a number of issues, not the least of which is that it doesn't just run vanilla pdflatex, ever. It runs in some strange box in which various pdflatex options have been changed from their default values. This would be fine if the arXiv system exposed its pdflatex or latex configuration. But it doesn't. Even better, since all the processing is done by robots, a "sandbox" robot could be established for people to test uploads before submission, greatly reducing the time wasted on this, not to mention the stress; documents and tarballs could be tested as they are being written and not "by fire" right at posting time.

Indeed, the inscrutable arXiv robot will reject a submission on any number of grounds, many of which are mentioned in the arXiv help pages, but few of which are described in enough detail for a user to reliably avoid them. For example, the figure size constraints (which were not our problem today) are never stated explicitly in the help pages; the help pages (like this one) only say that figures "should" be made "small" because that is more "efficient"!

As my loyal reader knows, I love the arXiv; it has transformed astrophysics and all of the sciences. Now lets just make it easier to use! Note that anything that makes it easier to use also makes it easier to maintain and run. (Think of all the emails and blog posts that could be saved!)