27th Year Reunion of Hayden Planetarium

It was kindof a reunion of some of the Digital Galaxy Protect from 1998.  Although many people were not there, Carter Emmart, Dennis Davidson and myself were there and I had a completely fabulous time. Loretta Skeddle may have been in the audience somewhere and Benjy Bernhardt was in Italy.

You can not imagine how sad I am that I am not able to be involved more with the Hayden.  

Notes on Adding Assets to the OpenSpace Project (OSP)

There is an open source project to provide a visualization framework to present astronomical data to the public called, logically enough, the OpenSpace Project (OSP).  It is in the grand tradition of the infrastructure of planetariums that stretches back in time to long before computer graphics and even computers.  The current state of the art uses graphics and projection hardware that would have been far too expensive for this purpose even a few years ago.

This particular framework seems to be a robust, somewhat comprehensive collection of the things one might need to put on a science show at a planetarium.  Time marches on, and so must the software.  It must permit new science to be incorporated into the core framework.

Furthermore,   the classic planetarium show has always been interactive and real time even when it has been rigorously scripted. Real time enables improvisation but it does not require it.   Every community has its traditions and the traditions of planetarium shows insist on this capability.

One of the principals of this project, Carter Emmart, a veteran of the ancient Digital Galaxy Project at the Hayden in NYC, asked me to add a very simple item to the repertoire of OpenSpace.  It should have been straightforward, but I have been pulling my hair out trying to get traction because, as we all know, writing documentation for a complicated piece of software like OpenSpace is non-trivial and not particularly pleasant.  OpenSpace does have documentation but not all documentation fits all use cases.

Systems of this type have very different classes of users and they all need different learning materials.  Some of these users will script new shows with the capabilities at hand.  Others will want to add to the functionality of the software.  Still others will be doing a masters or PhD thesis that incorporates visualization of science data or models into the software, but for their own use and not as a general capability.  Some of these people will be astrophysicists, some will be visualizers and some will be children.  So learning the software is likely to be painful depending on what your use case is.

This blog post will attempt to fill in some of these gaps for those who come after me.  The post will evolve as my understanding evolves.

The task at hand is to be able to create a type of lunar surface that exhibits the "retro reflection effect" for want of a better term.  Imagine you are in a lunar rover on the surface of the moon.  One of the observed phenomena is for light to be directed back at its source just as you might see from a reflected sign on a highway at night.  This phenomenon has been observed both on the moon and from earth.  It shouldnt be too hard to have OpenSpace simulate some version of this.

Notes for Adding New Geometry & Shader to OpenSpace

1. In general, types of data to be visualized with the OpenSpace Project (OSP) are defined as assets.  All assets are defined in text files with the suffix ".asset".

2. Assets can be added statically at the startup of OSP or interactively through the Lua console.  

3. The particular type of asset we want to add is called a RenderableModel.  See the documentation for this kind of asset at 

https://docs.openspaceproject.com/en/latest/generated/asset-components/RenderableModel.html

4. There are three fields in particular that interest us: the GeometryFile, the VertexShader and the Fragment Shader.

5. The GeometryFile will be the filename of a GLTF or GLB file.  This filetype is designed to encapsulate 3D geometry and many other things.  It is documented and maintained by Khronos and can be read about here:

https://registry.khronos.org/glTF/specs/2.0/glTF-2.0.html

6. The Vertex and Fragment shaders are individual text files which are compiled and downloaded to the relevant GPUs.  They contain the code necessary to actually render the surface in real time.  

7. Probably we will define this type of asset interactively using Lua, and therefore will need the scripting API documentation, which is documented here:

https://docs.openspaceproject.com/en/latest/generated/scripting-api/index.html

8. So, to my current understanding, I will be creating a new type of asset which points to some geometry, a vertex shader, and a fragment shader, and add this asset interactively via Lua.

No doubt this post will be updated as I learn more.

A New Star Catalog is Always a Cause for Celebration

A new star catalog is always a cause for celebration. Anyone who does more than dabble at astronomy visualization realizes that it is getting ahold of the data that is the sine qua non of serious work.

And yet getting the data is just the first of your many challenges. Very soon after downloading the data you will realize that one needs to have done some advanced study in astrophysics and/or have the services and advice of an astrophysicist or two in order to get anywhere. Without one or the other or both, the would-be visualizer will soon feel that he or she is lost in the forest on a moonless night.

But getting the data is the first necessary step, so it was with great pleasure that I read about the newly announced star survey with the catchy title of The second data release of the INT Photometric Hα Survey of the Northern Galactic Plane (IPHAS DR2)

And what is in this fabulous new survey?

The INT/WFC Photometric Hα Survey of the Northern Galactic Plane (IPHAS) is a 1800 deg2 imaging survey covering Galactic latitudes |b| < 5° and longitudes ℓ = 30°–215° in the r, i, and Hα filters using the Wide Field Camera (WFC) on the 2.5-m Isaac Newton Telescope (INT) in La Palma. We present the first quality-controlled and globally calibrated source catalogue derived from the survey, providing single-epoch photometry for 219 million unique sources across 92 per cent of the footprint. The observations were carried out between 2003 and 2012 at a median seeing of 1.1 arcsec (sampled at 0.33 arcsec pixel−1) and to a mean 5σ depth of 21.2 (r), 20.0 (i), and 20.3 (Hα) in the Vega magnitude system.

And so forth.

There are 219,000,000 unique sources in this survey. That is quite a bit more than the 10K star Yale Bright Star Catalog that we all grew up on. (1)

And yet there are certain similarities when you look a bit closer.   Certain subtle indications that suggest that the compilers of this fabulous expanse of data are adepts of the esoteric knowledge of astrophysics and that this data is intended for other members of this elite group.

In order to brace you for the tasks to come, should you decide to take on the challenge of visualizing this august data set, this post will present some first principles that are important for someone from the world of 3D as they step into the galaxy of creative decisions to be made and the arcane knowledge to master before the images latent in this esoteric compendium will be revealed.

I myself was first introduced to this knowledge during my brief but rewarding tenure on the Digital Galaxy Project portion of the rebuild of the Hayden Planetarium at the American Museum of Natural History in New York City.   Everyone on that project was a dedicated idealist with stars in their eyes.(2)

Because, you see, this dataset, like most astronomy datasets, is not intended to be for computer animation people. It is first and foremost to help scientists in the field, both those associated with the survey itself and those in the larger field of astrophysics, do their research. If people want to use it to “visualize the data” or make interesting pictures, that is all well and good, but that purpose is much further down the list of intended uses.

If we want to visualize the night sky what information would we ideally want? Well, we might want the 3D position of the stars, the brightness of the star, the color and presumably the type of star, as well as information about other objects in the sky that are not stars. This is a short list, there are actually many other things one might want to know for visualization purposes, but lets stop here. Ironically, a normal star survey or catalog does not generally have any of this information. At least not directly.

That is because what scientists are looking for in a star survey are the facts as they were observed. They may also be interested in your interpretations of the facts, but first and foremost they are interested in the data and how it was collected.

That means that instead of the 3D position of the “star” which we do not observe directly, except in a few exceptional cases, what the star catalog has is the position of the star as observed from earth on an imaginary 2D spherical coordinate system, a virtual sphere around the earth. In other words, the catalog does not say where the star is, but rather what direction it was observed to be from earth. The survey does not contain how bright the star was, or even if it was a star, but rather the spectra and intensity of the energy source as observed with the specific instrument. From that spectra, and from other information about the source of energy, one can deduce the type of star it probably is, but that is an interpretation of the data, not the data itself.

The star catalog or survey will not report the “color” as one normally thinks of such things, whether in RGB values, or CIE or other systems, but rather what was observed by the specific instrument or instruments used to collect the information. From the information in the catalog and the operating characteristics of the sensor one can derive spectra and from that a handy “color” in the visible bands if one so desires.

Nor is there any particular guarantee that the catalog is comprehensive, in some normal sense of the word. The authors of the catalog are not guaranteeing you that this survey contains all possible “stars” in the sky, or part of the sky. Instead what they are reporting here is the information about what they observed, and often some measure or estimate of how complete it is. The famous Messier catalog is not a complete list of anything, except the list of objects that Messier did not want to be bothered with anymore in his search for comets.

In a similar fashion, the data does not tell you how bright the star actually is, if it is a star, but tells you the intensity of the source as observed from earth. Again, an astrophysicist has various techniques to convert the apparent magnitude of the source to the absolute magnitude, if that is what you need.

The new star catalog has 219 million unique sources which may or may not be stars, and a variety of information about each, including some derived information (e.g. a probability that the specific source is indeed a star).

But it won't tell you anything about ISM (interstellar media), H2 regions and so forth.

When downloading the data, you can choose to download prepared datasets of the survey, or you can choose which data fields you want to review.  There are 99 different fields, and a dozen or so different formats you can get them in.  Just getting the data will probably take several days.

This post is the tip of the iceberg of what you need to know to do visualization from astronomy datasets but we will reserve these other topics for later posts.

The announcement can be found here

http://mnras.oxfordjournals.org/content/444/4/3230

The database can be found here

http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=IPHAS

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Notes

1. The Yale Bright Star Catalog is a famous dataset of the 10,000 or so brightest stars visible from earth. These are the stars that one could typically see from earth on a clear night with the naked eye from somewhere on the planet. It is a famous catalog in part because it was widely distributed even in days before the Internet or the Arpanet.

2. There were many, many people on this project which was part of a much larger project to rebuild the Hayden Planetarium and the entire north side of the American Museum of Natural History. Many people thought we were from Mars.  The cast of characters included such luminaries as Dennis Davison, Neil deGrasse Tyson, Carter Emmart, Frank Summers, Aram Friedman, Loretta Skeddle, Julio Morano, Benjy Benjamin, Ron Drimmel and many others.  And of course, your humble author, was also briefly a consultant on this project. 

The Amazing Planetarium Museum

In our post-sputnik world, the 1950s and the early 1960s, the US Government funded the creation of planetariums throughout the country to inspire our youth to dedicate their lives to science and so overthrow and defeat Godless communism.

I loved Planetariums, I love them still, but most of all I love the fabulous contraptions built to simulate the Universe on a dome above our heads.

One day, at the old Griffith Park Observatory, I hung out after a show and checked out the Planetarium control panel. It had big knobs like you found in 50s science fiction movies: and they had labels like "Comets", and "Beginning of Time", "The Planets", "Meteors. I realized suddenly that the true Planetarium was an interactive display, under the guidance and control of the master of ceremonies. There was probably a way to automate the shows, I am sure, but fundamentally, at heart, it was designed to be live and interactive.

There were only a few manufacturers of Planetariums, in fact, I was only aware of the big three: Zeiss, Minolta and Spitz until I came across this dedicated and comprehensive Planetarium museum. Now I know of a whole swarm of planetarium devices I had never heard of before.

Please review this site if you care about Planetarium history. I think he is trying to sell his collection, I wish I had not gone into Computer Animation so that I could afford to buy it.

See the museum here:

http://planetariummuseum.org/

Video clip of various planetariums spinning around

http://planetariummuseum.org/gonewld.wmv

Velikovsky and The Catastrophists

[I think the title of this piece would make a fabulous name of a band of some sort].

When I worked at the Hayden Planetarium, there were a few words you did not use in the presence of an astrophysicist.  Two of those words were "Immanuel Velikovsky", and if you were ever stupid enough to use those words in front of an astrophysicist, you made damn sure that they were not holding a cup of hot coffee or a knife, because out of instinct they would probably throw them at you.

Velikovsky was a "catastrophist", one of my favorite types of people.   Scientists went apeshit when they were faced with Velikovsky's ideas.

A "catastrophist" is someone who believes that the history of this planet has at various times been subject to dramatic events, or catastrophes, that cause a complete collapse of civilization and a restart, usually with no memory of what happened before, or very little memory.   Someone who believed in the biblical flood, for example, as a real historical event would be a catastrophist.   They might theorize that the story of Noah's Flood and of the exile from the Garden of Eden were dim memories of an earlier time and civilization,  handed down through the ages, however imperfectly.   Those who believe that Atlantis existed, but was destroyed by some disaster, would presumably also be catastrophists.   There may be a flavor of catastrophist to some of Lovecraft's work, e.g. the notion of the Elder Races.   Catastrophists can be said to write entertaining stories, in my humble opinion.  As science, that is another matter.

But when Velikovsky discussed his ideas, more formal and respectable scientists lost their minds and went nuts attacking him (so I hear).  Very undignified.   This book tries to explain what happened.

Read this review of a book on the topic.  Trust me.
http://cdn.lrb.co.uk/v34/n21/steven-shapin/catastrophism