I love learning about the data infrastructure that shapes the world we live in. Like all good infrastructure it’s usually invisible, because it just works. But there’s always something interesting to learn if you dig into the detail.
For example, a few years ago when I was researching how geospatial data is accessed, used and shared, I learned how quasars help us not just to find our way from A to B, but also help us get paid.
Everyone is familiar with GPS. There’s a network of satellites that span the globe constantly beaming their location and a timestamp down to earth. This allows GPS receivers, like the one in your phone, to figure out where they are on the planet.
But how do the GPS satellites know where they are? After all there are no fixed points in space.
It turns out that satellites, and other spacecraft, can use a different system called the International Celestial Reference Frame (ICRF) to identify where they are.
The ICRF defines a fixed frame of reference in space that is created by finding objects that are so far away in space that their position is essentially fixed.
There have been multiple versions of the ICRF but the most recent version came into effect in January 2019. It’s based on 40 years of observations of 4588 extragalactic radio sources, most of which are quasars. 303 of them define the basic axes of the frame and the rest fill in the detail.
Here’s a diagram that shows most of the sources:
The observations were taken by groups of between 2-20 radio telescopes. Working together they can operate as if they were a single very large telescope. This data is then shared and used to create the ICRF.
While the ICRF is primarily used for a range of astronomical research it’s a crucial part of ensuring the quality of the GPS system.
So those 4588 quasars are helping you get from A to B.
But what about helping you to get paid?
It turns out there are all kinds of other ways in which GPS signals can be used, for example as a remote sensing tool. This diversity of uses contributes to the economic impact of the GPS system which has been estimated at more than $1.4 trillion since the 1983.
That report makes for interesting reading and it includes an explanation of how the financial system makes use of GPS. Not as a means to navigate, but as a source of highly accurate timestamps.
High Frequency Trading requires the use of extremely accurate timestamps to ensure that trades are properly sequenced. Those timestamps broadcast by GPS satellites provide the level of accuracy that’s needed. So the modern stock market is now basically dependent on the GPS system. No stock market, no money.
Those timestamps are used not just in the stock market but in weather and energy systems. Which unfortunately can also makes them vulnerable to attack.
And that’s how 4588 extragalactic quasars help us not just to navigate and get paid, but contribute to understanding the world around us, at a distance of a billion light years. They help us run detect earthquakes, run our electricity systems and measure the impacts of climate change.
Like so much of our global data infrastructure the ICRF is built and maintained as a collaborative, open process. One which provides the foundations upon which most of our other data infrastructure is built.
As a final note, take a look back at that image above. Can you see that there are fewer dots in the bottom half of the image?
That’s because there are more radio telescopes in the Northern hemisphere. It’s not entirely inaccurate to say that the detail we can see in space reflect the economic conditions down on Earth. All datasets have flaws.
Lost Boy 