List of the most distant astronomical objects

This article documents the most distant astronomical objects discovered and verified so far, and the time periods in which they were so classified.

For comparisons with the light travel distance of the astronomical objects listed below, the age of the universe since the Big Bang is currently estimated as 13.787±0.020 Gyr.^[1]

Distances to remote objects, other than those in nearby galaxies, are nearly always inferred by measuring the cosmological redshift of their light. By their nature, very distant objects tend to be very faint, and these distance determinations are difficult and subject to errors. An important distinction is whether the distance is determined via spectroscopy or using a photometric redshift technique. The former is generally both more precise and also more reliable, in the sense that photometric redshifts are more prone to being wrong due to confusion with lower redshift sources that may have unusual spectra. For that reason, a spectroscopic redshift is conventionally regarded as being necessary for an object's distance to be considered definitely known, whereas photometrically determined redshifts identify "candidate" very distant sources. Here, this distinction is indicated by a "p" subscript for photometric redshifts.

The proper distance provides a measurement of how far a galaxy is at a fixed moment in time. At the present time the proper distance equals the comoving distance since the cosmological scale factor has value one: ${\displaystyle a(t_{0})=1}$. The proper distance represents the distance obtained as if one were able to freeze the flow of time (set ${\displaystyle dt=0}$ in the FLRW metric) and walk all the way to a galaxy while using a meter stick.^[2] For practical reasons, the proper distance is calculated as the distance traveled by light (set ${\displaystyle ds=0}$ in the FLRW metric) from the time of emission by a galaxy to the time an observer (on Earth) receives the light signal. It differs from the “light travel distance” since the proper distance takes into account the expansion of the universe, i.e. the space expands as the light travels through it, resulting in numerical values which locate the most distant galaxies beyond the Hubble sphere and therefore with recession velocities greater than the speed of light c.^[3]