4 ms·
The current coordinate system is based on extremely distant radio sources. Ground based scopes found some bright galactic sources which GAIA aligned to, and is
by gmiller123456 2y ago
The current coordinate system is based on extremely distant radio sources. Ground based scopes found some bright galactic sources which GAIA aligned to, and is measuring everything relative to those. And now GAIA is the defining source of the ICRS for optical observations.