Just to explain it further: The 8 is around New York and the 7 is around Texas (up and down tho 'cause it's time zones) and if you live one time zone left from Central Time you'd have the show at 6 and so one
The U.S. covers 9 time zones, 4 across the contiguous states going, from east to west, Eastern, Central, Mountain, Pacific. Hawaii and Alaska each have their own time zone and the remaining 3 cover our territories. As shows are broadcasted simultaneously across the entire of the U.S. it is easier for companies to merely state times based upon the most populous Eastern time zone with the central time added on as a reminder. So when they say 8/7c it means 8 o'clock Eastern Time, 7 o'clock Central time. From there anyone watching can easily determine their own respective start time.
http://www.timetemperature.com/tzus/time_zone.shtml
This source also has a map showing the time zones.
http://www.timetemperature.com/tzus/time_zone.shtml
This source also has a map showing the time zones.