RealEarth is a server-based data visualization system developed at SSEC/CIMSS, University of Wisconsin-Madison that provides satellite imagery and related data products to desktop and mobile clients. It is built on open source software including, MapServer, GDAL, Proj4, PHP, and Python. The purpose of RealEarth is to provide a simple interface for data visualization and comparison across the atmospheric, oceanic, and Earth science domains.