Satellite radio is a relatively new entrant into the radio market. Traditional radio stations broadcast their programs via large antennas to provide reception in the surrounding area. The most powerful broadcasts are accessible over 100 miles from the source, although most broadcasts reach about 35 miles.
As the name suggests, satellite radio uses satellites to deliver audio content to huge swaths of land. XM, Sirius are two such services that provide satellite radio broadcasts and their signals are available all over the United States. Worldspace provides digital broadcasts for most other places in the world. Satellite radio signals are broadcast in digital form which drastically improves the quality of reception. In fact, the quality of these digital broadcasts approaches that of CD audio!
Both XM and Sirius offer around 100 stations and Worldspace's programming guide seems to be growing and growing. Many of the programs are either commercial free or close to it. Programming varies from news to talk to all sorts of music stations.
Receiving satellite broadcasts requires special satellite receivers, and the service also requires a payment, usually around $10 per month. The first satellite radios were installed in cars, but now more and more are becoming available for the home and in portable devices.