Parsec
Volume units

To determine the number of stars in the Milky Way, volumes in cubic kiloparsecs (kpc) are selected in various directions. All the stars in these volumes are counted and the total number of stars statistically determined. The number of globular clusters, dust clouds, and interstellar gas is determined in a similar fashion. To determine the number of galaxies in superclusters, volumes in cubic megaparsecs (Mpc) are selected. All the galaxies in these volumes are classified and tallied. The total number of galaxies can then be determined statistically. The huge Boötes void is measured in cubic megaparsecs.

In physical cosmology, volumes of cubic gigaparsecs (Gpc) are selected to determine the distribution of matter in the visible universe and to determine the number of galaxies and quasars. The Sun is currently the only star in its cubic parsec, (pc) but in globular clusters the stellar density could be from 100–1000 pc.

The observational volume of gravitational wave interferometers (e.g., LIGO, Virgo) is stated in terms of cubic megaparsecs (Mpc) and is essentially the value of the effective distance cubed.
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