An artist can get music on the Billboard charts by receiving a relatively higher amount of sales and/or airplay compared to other artists data tabulated for said chart in a given reporting week.
There are various Billboard Charts (i.e. Singe Sales Chart, Hot 100 - see full list at Billboard.com/charts) and the data for each chart is typically compiled from sales and/or radio play data reported to Neilsen Soundscan (also known as "Soundscan").
Radio play data used in tabulating certain Billboard chart standings is reported to Soundscan by Radio stations. The Sales data is reported by outlets in the following three categories:
Retail sales are reported by music retailers like Wal-Mart, Best Buy and independent stores, both via brick-and-mortar outlets and via physical sales via their online websites. Some of the same sites report Online / Digital sales, along with popular digital retailers like iTunes and Rhapsody.
Venue sales are typically reported by Record labels or National Distributors who handle independent artists and indie labels.
Unsigned or independent artists, who are often by definition artists without a Record Label or Distribution deal, are able to report Retail Sales via consignment deals and Online / Digital Sales via various music agregators (CDBaby, etc). These same artists are typically only able to report venue sales to Soundscan through services like IndieHitMaker.com. You could also try www.dittomusic.com who register unsigned artists with the Billboard charts.
There were no billboard charts in 1951. Billboard charts did not begin until 1958
Charts music is music that qualifies for inclusion in any of the Billboard music charts.
On the U.S. Billboard Charts: Sean Kingston - Beautiful Girls On the U.K. Billboard Charts: Kanye West - Stronger
The rock charts began in January, 1955
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Billboard
The song "Our Day Will Come" by Ruby & the Romantics topped the Billboard charts on March 17, 1963.
The Billboard magazine has 123 ongoing music charts in different categories (Jazz, Rock, R&B, Country, Album, etc.). There are even charts for ringtones.
On the U.S. Billboard Charts: Debby Boone - You Light Up My Life On the U.K. Billboard Charts: David Soul - Silver Lady
creep by TLC
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Billboard