Galaxy Is 30 Billion Light Years Away

z8_GND_5296 is a galaxy which, after its discovery in October 2013, was announced as the galaxy with the greatest redshift that has been confirmed through the Lyman-alpha emission line of hydrogen, putting it among the oldest and most distant known galaxies at approximately 30 billion light-years from Earth. It is "seen as it was at a time just 700 million years after the Big Bang [...] when the universe was only about 5 percent of its current age of 13.8 billion years". The galaxy is at a redshift of 7.51, and it is neighbour to what was announced then as second most distant galaxy with a redshift of 7.2. The galaxy in its observable timeframe was producing stars at a phenomenal rate, equivalent in mass to about 300 per year.

The light reaching Earth from z8_GND_5296 left that galaxy over 13 billion years ago, corresponding to a distance of over 13 billion light-years. In accordance with the prevailing theory of an expanding universe, the observed position of the galaxy is now much farther away, about 30 billion light-years (comoving distance) from Earth. [See discussion of comoving distance below]

Discovery
Research published in the October 24, 2013 issue of the journal Nature by a team of astronomers from The University of Texas at Austin led by Steven Finkelstein in collaboration with astronomers at the Texas A&< University, the National Optical Astronomy Observatories and Univerisity of California, Riverside, describes discovery of the most distant galaxy known using deep optical and infared images taken by the Hubble Space Telescope. Their discovery was confirmed by the W. M. Keck Observatory in Hawaii. MOSFIRE (a new instrument on the Keck Telescope that is extremely sensitive to infared light) proved instrumental to this finding.


To measure galaxies at such large distances with definitive evidence, astronomers use spectroscopy and the phenomenon of redshift. Redshift occurs whenever a light source moves away from an observer. Astronomical redshift is seen due to the expansion of the universe, and sufficiently distant light sources (generally more than a few million light years away) show redshift corresponding to the rate of increase in their distance from Earth. The redshift observed in astronomy can be measured because the emission and absorption spectra fof atoms are distinctive and well known, calibratedd from spectroscopic experiments in laboratories on Earth.
  http://en.wikipedia.org/wiki/Z8_GND_5296

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Comoving Distance
In standard cosmology, comoving distance and proper distance are two closely related distance measures used by cosmologists to define distances between objects. Proper distance roughly corresponds to where a distant object would be at a specific moment of cosmological time, measured using a long series of rulers stretched out from our position to the object's position at that time, and which can change over time due to the expansion of the universe. Comoving distance factors out the expansion of the universe, giving a distance that does not change in time due to the expansion of space (though this may change due to other, local factors such as the motion of a galaxy within a cluster). Comoving distance and proper distance are defined to be equal at the present time; therefore, the ratio of proper distance to comoving distance now is 1. At other times, the scale factor differs from 1. The universe's expansion results in the proper distance changing, while the comoving distance is unchanged by this expansion because it is the proper distance divided by that scale factor.

http://en.wikipedia.org/wiki/Comoving_distance