Whilst NTSC does have 525 "lines", it only defines 480 of those for active picture, the rest were left delays during monitor flyback (as the beam goes from the bottom to the top of ur TV), and other uses/future expansion (such as timecode, closed caption, teletext, test signals, etc).
So unless you want to view a lot of lines of blank/data/test signals you're only really interested in the 480 active picture lines.
...Actually, since it's an analogue signal, the "effective" horizontal resolution of television signals is limited only by the bandwidth of the luminance and chroma circuits of your receiver/TV...
Well, to some extent, but not really, since video signals are bandwidth limited to 5MHz at source, well before they even get anywhere near your reciever/TV. Plugging the appropriate numbers into an equation to work out the maximum possible horizontal frequency in a 525-line (ie NTSC) system, gives you 317 cycles per line, which gives a max of 634 "pixels"/line.
You can throw numbers at a PAL system and get similar answers.
FWIW the horizontal resolution of 720 pixels probably has a lot more to do with the length of an active line in ITU/CCIR 601 digital video (SDI) than anything else.
Although it will probably be re-dubbed with an American accent and dumbed down for the US market. The joint BBC & Discovery documentaries are edited differently, and "dumbed down", for the US market. It seems that the American networks find it hard to get people to watch an educated documentary.
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Whilst NTSC does have 525 "lines", it only defines 480 of those for active picture, the rest were left delays during monitor flyback (as the beam goes from the bottom to the top of ur TV), and other uses/future expansion (such as timecode, closed caption, teletext, test signals, etc).
So unless you want to view a lot of lines of blank/data/test signals you're only really interested in the 480 active picture lines.
...Actually, since it's an analogue signal, the "effective" horizontal resolution of television signals is limited only by the bandwidth of the luminance and chroma circuits of your receiver/TV...
Well, to some extent, but not really, since video signals are bandwidth limited to 5MHz at source, well before they even get anywhere near your reciever/TV. Plugging the appropriate numbers into an equation to work out the maximum possible horizontal frequency in a 525-line (ie NTSC) system, gives you 317 cycles per line, which gives a max of 634 "pixels"/line.
You can throw numbers at a PAL system and get similar answers.
FWIW the horizontal resolution of 720 pixels probably has a lot more to do with the length of an active line in ITU/CCIR 601 digital video (SDI) than anything else.
Although it will probably be re-dubbed with an American accent and dumbed down for the US market. The joint BBC & Discovery documentaries are edited differently, and "dumbed down", for the US market. It seems that the American networks find it hard to get people to watch an educated documentary.