Geller and Huchra Spectrograph

Lent by the Smithsonian
Astrophysical Observatory

This spectrograph (a device for recording the spectra of galaxies) was used to collect the data for a 3-D map of one section of the observable Universe. The map was created by astronomers Margaret Geller and John Huchra of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.

To create the 3-D image, Geller and Huchra mapped the location in the sky of each of thousands of galaxies. To plot the galaxy's location in the third dimension, they had to figure out its velocity. This instrument spread the light from each galaxy into a spectrum and recorded it electronically. Analyzing the spectrum revealed how fast the galaxy was moving toward or away from us. A computer plotted the resulting data in three dimensions.

Spectrograph Observations

Courtesy of Margaret Geller,
Smithsonian Astrophysical Observatory

This is a three-dimensional map of one section of the observable Universe. Each dot represents a galaxy. The galaxies are not spread evenly, but form a vast lacework of filaments, sheets, and bubbles. Our Milky Way galaxy is located at the point where the "slices" converge. The farther a galaxy is from the center, the faster it is moving away from us. After more of the Universe is charted in detail, the map will form a sphere.

The map created by Margaret Geller and John Huchra was the first to clearly show large-scale, three-dimensional structure in the Universe. Their work and that of others sparked the development of new ways to automatically sample very large and deep volumes of space. More than a dozen different projects worldwide are now probing deeply into the Universe to examine its large-scale structure.