The digitization of astronomy

The first paper in the 1 December 1962 issue of Physical Review Letters bore the title “Evidence for x rays from sources outside the solar system.” Forty years later, the paper’s lead author Riccardo Giacconi shared the Nobel Prize in Physics for what the paper portended: the opening of the x-ray cosmos to astronomical exploration.

When I decided to become an x-ray astronomer in 1984, the field was 22 years old, just like me. The newness was part of its appeal. Being centuries older, optical astronomy has accreted a plethora of offputingly obscure terms. To see what I mean, check out the Wikipedia entry on the spectral classification of stars. It contains such gems as “The reason for the odd arrangement of letters is historical” and “O, B, and A stars are sometimes misleadingly called early type.”

Another of x-ray astronomy’s attractions for me is that the data are inherently digital, by which I mean discrete. The first x-ray detectors were simple Geiger counters, whose active medium is a noble gas subjected to an electric field. Whenever an x-ray photon passes through the medium, the resulting ionization produces a single pulse of charge.

More advanced detectors work on the same principle. A photon’s energy spawns a countable number N of electrons, electron–hole pairs, phonons, Cooper pairs, or other particles. At least from the point of view of statistics, reducing and analyzing x-ray data is usually straightforward.

Other digitizations

Like other graduate students, I was rather focused on my thesis research. Even so, I was aware that optical and IR detectors were becoming digital. One of my contemporaries at the Institute of Astronomy in Cambridge, Chris Haniff, was working with Craig McKay on applying CCD technology to astronomical imaging.

Now, pretty much all detectors from IR to gammas are digital in the sense that they count individual photons. But in popular as well as technical parlance, digital can also refer to the use of computers to store, transmit, and analyze data.

A building on the grounds of the Institute of Astronomy housed the Automatic Plate Measuring machine, a device the size of a skip that automatically digitized photographic plates taken by the UK Schmidt Telescope at Siding Spring Observatory in Australia.

Schmidt telescopes have wide fields of view and are used for surveys. By digitizing plates and processing the data they contained, the APM made it possible to systematically classify and study stars, galaxies, and other celestial bodies.

Another of my grad school contemporaries, Stephen Warren, figured out a way to make quasar candidates more conspicuous in APM data. I was in the office we shared when he received a congratulatory phone call from a colleague at the Anglo-Australian Telescope. One of his APM-selected candidates turned out to be first redshift-4 quasar discovered.

Observers aren’t the only digital astronomers. I remember chatting with the institute’s system administrator after she’d warned the observatory’s staff and students to be more frugal in their use of data storage. “Who are the biggest data hogs?,” I asked. “Theorists!” she replied. Then as now, theorists can create what amount to a series of simulated observations whose resolution and data footprints far exceed those of real observations.

Later in my career, when I was a researcher at NASA’s Goddard Space Flight Center, I witnessed other significant developments in the digitization of astronomy. Astronomers began to archive data in standard, easy-to-use formats, the World Wide Web—notably the arXiv e-print server—promoted communication among astronomers, and conducting observations away from the telescope became routine.

The next advance in the digitization of astronomy might be in the visualization of data. Computational astronomers already rotate and look inside their simulations in much the same way that biologists view crystallographically derived molecular structures. But as far as I know, visualization hasn’t yet reached the point that it could help lead astronomers to new discoveries.

Thanks to Patrick McCray for inspiring this post and providing its title.