What time can be called "dusk"? Studies have shown that outdoor light decreases rapidly during the 30 minutes following sunset. It is this fast change from daylight to darkness that makes it harder to drive or walk, not just the dimness. This 30-minute span is called "dusk", while sunset is defined as the time when the sun disappears below the horizon.
As Figure 2 shows, the time of sunset differs depending on the region (latitude and longitude) and season.
The seasonal difference is approximately two hours (June and July vs. November and December), far greater than the regional difference, which is 30 to 40 minutes (e.g. between Ibaraki Prefecture and Fukuoka Prefecture). The regional gap is therefore disregarded in the following analysis.
|
