the time of the line

what time is it in new york? what time is it in paris? what time is it in vienna? a line links the three cities, perhaps not a straight line, but sure enough a straighter line than new york, paris, rome. but even if the line is straight, there is difference in time. new york is not the same time as paris, but paris is the same time as vienna. noon in new york; six o'clock in paris and vienna. but the more or less straight line that new york-paris- viena makes does not make the same difference in time. and even though paris and vienna are the same time, it still takes another two hours (by plane) to get there. yet again, one might say that new york, paris and vienna, in the 1980's are of the same time. but what time?