Glossary
Help
 Archive Intro
 Table Descriptions
 Schema Browser
 Glossary
 Algorithms
 Introduction to SQL
 Form Query User Guide
 Query Limits
 How To
 FAQ
 API
 sdssQA
 Download
 SkyServer Sites
 Web Browsers
 Contact Help Desk

nametext
magnitude, PetrosianStored as petroMag. For galaxy photometry, measuring flux is more difficult than for stars, because galaxies do not all have the same radial surface brightness profile, and have no sharp edges. In order to avoid biases, we wish to measure a constant fraction of the total light, independent of the position and distance of the object. To satisfy these requirements, the SDSS has adopted a modified form of the Petrosian (1976) system, measuring galaxy fluxes within a circular aperture whose radius is defined by the shape of the azimuthally averaged light profile.