Where Are We in Space? Astronomers Update Their Celestial Frame of Reference

By Ryan F. Mandelbaum on at

How do you know where anything is in space? Sure, you can say, “Oh, that star, it’s the one in the middle of the Big Dipper,” but that’s not very useful in an era of incredible telescopes peeping at galaxies billions of light-years away. On January 1, 2019, scientists will adopt the newest, internationally standardised frame of reference to help locate things in space.

The third edition of the International Celestial Reference Frame, or ICRF-3, is the most up-to-date version of the International Astronomy Union’s standardised reference frame. Imagine the universe as a graph from geometry—scientists need a place to put the origin and axes.

“Nitty-gritty stuff like this is super important when you’re sitting on an Earth moving 70,000 mph around a star that is moving 450,000 mph around a galaxy centre,” Grant Tremblay, astrophysicist at the Harvard-Smithsonian Center for Astrophysics, told Gizmodo.

Every physics problem starts with an innate step you might not realise: determining where the problem is taking place and the coordinates you’ll use to watch the physics happen. Astronomers need to do this, too, like drawing a graph in space.

The ICRF-3 is the latest update to our reference frame, following ICRF-1 from 1998 and ICRF-2 from 2009. It places the centre of the reference frame at the Solar System’s centre of mass, and is oriented based on the position of distant bright radio sources called quasars. Those measurements were made using Very Long Baseline Interferometry (VLBI), essentially a method of using the entire Earth as a telescope, collecting data from multiple radio telescopes and combining them to get the highest-resolution image possible.

This most recent frame derives from measurements of 4,536 quasars, all between 100 million and 10 billion light-years away. At these distances, they’re basically stationary. The most recent edition also takes the motion of our own Milky Way galaxy into account for the first time, according to a press release from the Helmholtz Centre Potsdam.

So, now we can determine where we are, more precisely than before, in the incomprehensibly vast cosmos. I hope this offers some comfort.

Featured image: Illustris Collaboration