GTN banner
Goddard Space Flight
													      Center Sonoma State University
													  Education and Public

Statistical Summary

Distribution to fixed brightness

The observed distribution for bright galaxies is as follows.

spirals 77%
ellipticals 20%
irregulars 3%

This was the observed distribution known as of the middle of the 20th century. This is the distribution appropriate for the NGC catalog and for bright galaxies identified from photographic surveys. This distribution would not be appropriate for results obtained from deep surveys with the Hubble Space Telescope or from large contemporary ground based telescopes or from modern surveys such as the Sloan Digital Sky Survey (SDSS).

Since spiral galaxies are particularly easy to distinguish from stars, there is some expectation that more spirals will be represented in this sample than would be present if we could sample the total number of galaxies in a volume of space.

Distribution to a fixed volume

The distribution observed in a fixed volume of space out to a radius of about 9.1 Mpc is as follows.

spirals 33%
ellipticals 13%
irregulars 54%

The high percentage of irregulars in this sample may be a reflection of the difficulty of resolving detail for distant galaxies. Alternatively, it may be a reflection of the fact that we tend to "see" spirals more easily than other types of galaxies and in reality many galaxies are less well formed or organized than the bright spirals that attract our attention in casual images of the sky.

Modern results obtained from automated classification of deep images using digital media confirm the suggestion that fainter, more distant, younger galaxies tend to be less well organized than the older galaxies we see in our local region of the universe at the present time.

If you have a question about the GTN, please contact one of the "Responsible SSU Personnel" below.

This page was last modified on Saturday 31st January 2009 @ 12:15pm

Science Mission Directorate Universe Division

Responsible SSU Personnel:

Dr. Kevin McLin (mclin at universe dot sonoma dot edu)

Privacy, Security, Notices