Mapping the Universe - Mapping Scientific Frontiers: The Quest for Knowledge Visualization - page 70

cosmic magnification caused by the gravitational effect of dark matter throughout
the universe with observations of 13 million galaxies and 200,000 quasars from the
SDSS.
SDSS generates a vast volume of astronomical data of large-scale structures,
galaxies, quasars, and stars. It has made a series of data releases to the public. The
website for publicly-released data ( skyserver.sdss.org ) receives millions of hits per
month. In parallel, astronomers have used SDSS data in their research and produced
a rapidly growing body of scientific literature.
Mapping the universe is a dream of many generations. The first map of
the universe is the Logarithmic Map of the Universe 3 , created by a group of
astronomers, including Richard Gott, Mario Juric, and David Schlegel, and Michael
Vogeley. The logarithmic map depicts the entire visible Universe in a rectangular
shape with the Earth as the bottom line of the map and the Big Bang as the top
of the map. The rectangular map includes SDSS galaxies and quasars as well as
astronomical objects that one can see from the Earth, such as the Sun, the moon, and
stars in famous constellations. A computer printout of the map stretches from the
floor all the way to the height of an office door. Figure 2.23 shows part of the map.
This portion of the map shows astronomical objects beyond 100 megaparsecs (mpc)
from the Earth. The scale in mpc is shown on the left-hand side of the map. At about
100 mpc, there is the CfA2 Great Wall. Coma Cluster is about the same distance
from the Earth. The Sloan Great Wall is located about 120 mpc. Because the map
is on a logarithmically transformed scale, the upper part of map is compressed at a
higher rate than the lower part of the map. SDSS galaxies start from about 100 mpc.
SDSS quasars started from about 2,000 mpc. Several high redshift SDSS quasars
are marked on the right-hand half of the map with ' C ' signs. Near the top left strip
just passed the 1,000 mpc, a dashed line is marked the birth of the first stars after the
Big Bang. Above the dashed line is a line for cosmic microwave background. Right
above of it, a solid line marks the time of the 'Big Bang.'
A point on the celestial sphere can be identified by its right ascension and
declination degrees. The rectangular map contains the positions of SDSS galaxies
and quasars in terms of right ascension and their distances measured from the Earth.
With the rectangular map, viewers can easily tell how far away an astronomic
object or structure is from us. Figure 2.24 shows a circular map of the universe
we generated in 2007 based on the SDSS data. The map was selected by the 3rd
iteration of the Places & Spaces in 2007. In 2008, a modified version of the map
was entered to the NSF and Science & Engineering Visualization Challenge and
received a semifinalist award.
The circular map of the universe depicts astronomical objects and scientific
activities associated with some of the astronomical objects. The radius of the
circular map represents the look-back time, or the approximate time elapsed from
the beginning of the universe. The further away from the Earth an object on the map,
the closer it was to the beginning of the universe. Figure 2.25 shows the sketch of
3 http://www.astro.princeton.edu/universe/