The angular correlation function is a function which measures the projected clustering of galaxies, due to discrepancies between their actual and expected distributions. The function may be computed as follows: w ( θ ) = 1 N d P d Ω − 1 {\displaystyle w(\theta )={\frac {1}{N}}{\frac {dP}{d\Omega }}-1} , where P {\displaystyle P} represents the conditional probability of finding a galaxy, Ω {\displaystyle \Omega } denotes the solid angle, and N {\displaystyle N} is the mean number density. In a homogeneous universe, the angular correlation scales with a characteristic depth.
References
The Galaxy Angular Correlation Functions and Power Spectrum from the Two Micron All Sky Survey https://ui.adsabs.harvard.edu/abs/2005ApJ...619..147M/abstract ↩
"B. The correlation function: galaxies". Retrieved 2021-06-09. https://ned.ipac.caltech.edu/level5/March04/Jones/Jones5_2.html ↩