NASA and an international boffinry alliance are chuffed to announce that they have successfully updated the map grid of the entire universe. Just as old-time sailors used the stars to navigate the Earth's oceans, spacecraft plying the infinite void of space - and astronomers probing it - will use quasars a billion lightyears away as reference points.
The reasons for using quasars in space mapping are the same as those behind the use of stars in nautical navigation, according to NASA's Dr Chopo Ma. In either case you need to use reference points so far away that their motion can't be detected, giving you a fixed frame against which to plot your own location or that of an object - an island or a rock or a ship back then, a star or a planet or a spacecraft now.
One application of the quasar-fixed International Celestial Reference Frame (ICRF) is the precise location of GPS satellites, for instance.
"For GPS to work, the orbital position, or ephemeris, of the satellites has to be known very precisely," says Ma. "In order to know where the satellites are, you have to know the orientation of the Earth very precisely."
You could use stars for that - people used to.
"However, for the extremely precise measurements needed for things like GPS, stars won't work, because they are moving too," explains Dr Ma. "Everything is always moving," he adds, rather bitterly.
The solution is to use quasars. They're probably moving too, but they're so incredibly unfeasibly far away that you can't tell, so it doesn't matter. The initial ICRF, based on 600-odd of the mysterious faraway radiation-emitting objects, was completed in 1995. (Nobody's totally sure what a quasar actually is, hence the name. A popular theory is that they result from massive amounts of stuff - perhaps entire galaxies - falling into incredibly enormous black holes and emitting vast amounts of energy as they are wracked and mangled out of existence.)
It seems that the original ICRF was getting out of date, though, so an international boffinry league was set up by Australia, Austria, China, France, Germany, Italy, Russia, Ukraine, and the US to rectify this. The new and better ICRF2, based on 3,000 quasars as compared to the measly 600 of the first grid, was completed this year and rated as pukka by the International Astronomical Union (IAU).
According to Ma, who bossed the ICRF2 plotting for NASA, the new space grid will be used for plenty of other things besides GPS and satellites. Astrogators aboard the possible interplanetary craft of tomorrow will plot their courses on ICRF quasar-fixed star charts; and, much more often probably, astronomers will lay down the positions of things they find in similar wise.
Meanwhile for Ma the grind goes on - it's already time to start thinking about the next ICRF update. ICRF2 was done using Very Long Baseline Interferometers (VLBIs, basically groups of radio telescopes hooked up to form mighty intergalactic spyeyes of unimaginable keenness), but that's getting to be old hat now.
The Gaia satellite planned for 2012 will be able to clock no less than half a million quasars, producing an ICRF3 that will make today's look like a smudgy map of the UK printed on a cheap tea-towel.
There's more from NASA here. ®