The answer lies in its density, and according to a group of American astronomers the distortion of light by the gravity of nearby galaxy clusters may provide a way to measure it. (newscientist.com)
Most direct estimates of the constant are, in fact, based on observations of relatively nearby galaxies. (newscientist.com)
However, until now, radio telescopes have only been able to detect the emission signature of hydrogen from relatively nearby galaxies. (sciencedaily.com)