Using the 2dF instrument, the 2dF Galaxy Redshift Survey (2dFGRS) team set out to measure the redshifts of, and hence the approximate distances to, more than 200,000 galaxies. Instead of covering the whole sky superficially, they concentrated on mapping in great detail two strips, one in the summer night sky, and the other visible in winter. Each strip is around 80 degrees long and 10 degrees wide. Because the survey looked at all the bright galaxies within some fixed angle on the sky, each strip opens out with increasing distance from us, creating a triangular survey region. The number of galaxies decreases with distance because at large distances only rare extremely luminous galaxies appear bright enough to be included in the survey. In addition, the team surveyed the galaxies in a number of small fields away from the main slices, creating further “pencil beam” maps in these directions.
A two-dimensional representation of the distribution of galaxies in the 2dFGRS, made by projecting the two main “slices” onto a flat plane. The Milky Way is located where the slices meet in the middle (the map of the Milky Way would be far too small to be seen at this scale).
The resulting three-dimensional distribution of galaxies provides the largest map to-date of a representative section of the Universe. Looking at this map, it is apparent that the Universe is permeated by a complex web of filamentary structures and huge almost-empty voids.
The scale of this map is truly mind-boggling. Even travelling at the speed of light (around 300,000 kilometres per second), the light emitted by stars in the most distant galaxies has taken some two billion years to travel all the way to Earth, where it just happened to land on the Anglo-Australian Telescope when the telescope was pointed in the right direction, and thus was preserved for posterity as a spectrum in the 2dF Galaxy Redshift Survey. In order to be reproduced as a sculpture, the scale had to be reduced by a factor of a billion billion billion.