First, let's be precise about what "Evening Civil Twilight" means — Page 457, Lesson 453

I want to walk you through the Evening Civil Twilight table. This is a standard navigation table you'll use to find when civil twilight ends at a given latitude on a given date. First, let's be precise about what "Evening Civil Twilight" means. Civil twilight is the period after sunset when the centre of the sun is between 0° and 6° below the horizon. Evening civil twilight ends at the moment the sun's centre reaches 6° below the horizon — that's when it becomes too dark for normal outdoor activities without artificial light. The table gives you the time of that ending, in hours and minutes. Now, look at the structure. The table is organised by latitude down the left-hand side, in degrees North — you can see N72, N70, N68, N66, N64, N62, and N60. Across the top, the columns are the dates, running from November through December into January. The dates are listed as day numbers — 19, 22, 25, 28, then 1, 4, 7, 10, 13, 16, 19, 22, 25, 28, 31, then 3. So the table spans from 19 November through 3 January. Each cell contains a time in hours and minutes — for example, at N72 on 19 November, the time is 14 hours 38 minutes. That's the local time at which evening civil twilight ends at that latitude on that date. Let me read you a few values so you can see the pattern. At N72, the times run from 14:38 on 19 November, decreasing to 12:59 around late December, then rising again to 13:31 by 3 January. At N60, the bottom row, the times start at 16:13 on 19 November and decrease to 15:50 around mid-December, then rise again. Notice the key behaviour: the times get earlier as you go from November into December — twilight ends sooner — and then they get later again as you move into January. That's the seasonal swing. Also, for the same date, higher latitudes have earlier twilight-ending times than lower latitudes. Compare N72 at 14:38 with N60 at 16:13 on the same date — the higher latitude ends twilight more than an hour and a half earlier. There's a figure in the book that shows the creation of the grid for this kind of table — . That's the layout of how the latitude rows and date columns are built. One thing to note: the table is for Northern latitudes only — the values are all labelled N. For Southern latitudes you'd use the corresponding table for the opposite season. So, in practice: you enter the table with your latitude and the date, and you read out the time of evening civil twilight ending. That time is what you'd use for planning when darkness begins for your flight operations.