Twilight (time) zones

You may have heard the song with the words "it's twilight time"; it may even be called that. But who knew that there are actually three twilight each day (counting only those that happen when the sun is setting) - Civil (the period between day and night when it is possible to conduct outdoor activities without artificial light); Nautical (the horizon is still visible allowing navigational readings to be done accurately) and Astronomical (stars and other point sources visible but not nebulae and galaxies).. The differentiation is based on how many degrees the sun is below the horizon - Civil - less that 6; Nautical 12-6; Astronomical 18-12. (With thanks to Wikipedia - which also notes the differentiation is important because the penalty for some crimes (presumably in the US) eg burglary is greater if they are conducted outside of daylight hours.)