It's relative to Sagittarius A* , the black hole at the center of our galaxy, which this star is orbiting. Or you could say relative to our galaxy, since Sagitt

It's relative to Sagittarius A* , the black hole at the center of our galaxy, which this star is orbiting. Or you could say relative to our galaxy, since Sagittarius A* appears to be stationary within it. However, 8% of the speed of light (24000 km/s) is so fast that the orbital speed of the sun in the galaxy (200km/s) and the orbital speed of the Earth around the sun (30km/s) are negligible in comparison. So you might as well say that it is relative to Earth.