Let me set the scene — Page 440, Lesson 406

I want to walk you through what this page actually is, because at first glance it looks like a wall of numbers. This is a table of evening civil twilight times — and it's one of those pages in General Navigation that pilots use to plan when daylight operations are possible. Let me set the scene. The table is laid out by latitude down the left-hand side — you can see N72, N70, N68, N66, N64, N62, N60 — and by date across the top, running from December through January and February. So for any given latitude and any given date in that winter window, the table gives you the time of evening civil twilight. Now, what do I mean by civil twilight? This is the precise definition you need. Civil twilight is the period when the centre of the sun is between 0° and 6° below the horizon. In plain terms, it's the time after sunset when there's still enough natural light to carry out ordinary outdoor activities without artificial lighting. For aviation, this matters enormously — it defines the legal and practical limit of daylight flying. When civil twilight ends, you're into the period where you need to treat operations as night flying. So the times in this table — let me read one for you so you can see how the format works. Take latitude N72 on, say, the first date column. The entry reads 13 17 — that's 13 hours and 17 minutes. So evening civil twilight occurs at 13:17. Look down the row and you'll see the times progress: 13 27, 13 40, 13 53, 14 07, 14 21, 14 36, 14 50, 15 05, 15 19, 15 34, 15 48, 16 02, 16 16, 16 30, 16 44, 16 58. Notice the pattern — as the days move from December into January and February, the evening civil twilight time gets later and later. That's the sun setting later as winter gives way to spring. Now look at what happens as you move down the latitudes. At N70, the first entry is 14 13 — later than N72's 13 17. At N68 it's 14 47. At N66, 15 11. At N64, 15 30. At N62, 15 46. At N60, 15 59. Do you see the relationship? The lower the latitude, the later the evening civil twilight time for the same date. That makes sense — closer to the equator, the sun sets later in the winter, and the twilight lasts longer into the evening. Let me also point out the column structure, because you'll need to read this table quickly in an exam or in flight planning. The header row shows the months — December, January, February — and beneath each month there are columns labelled h and m, for hours and minutes. So each date column gives you a time in hours and minutes. The numbers are grouped in a way that lets you read across: for example, at N70 you'll see 14 13, 14 19, 14 27, 14 36, 14 46, 14 57, 15 08, 15 19, 15 31, 15 43, 15 55, 16 07, 16 19, 16 31, 16 43, 16 55, 17 07. Each pair is a time — hours then minutes. There's one more thing I want you to notice, and it's a subtle but important detail. Look at the very top of the page — you'll see a row that reads 5 46, 5 47, 5 48, 5 48, 5 49, 5 49, 5 49. That's not part of the twilight table itself. That looks like a page reference or a section marker — it's telling you which pages of the source material this table belongs to. Don't get confused by it; it's just navigation metadata for the book, not data you need to fly with. So let me summarise what you should take away from this page. You have a table of evening civil twilight times, organised by latitude (N60 to N72) and by date (December through February). Each entry is a time in hours and minutes. The key relationships are: for a fixed latitude, twilight gets later as the season progresses; for a fixed date, twilight gets later as latitude decreases. And the definition you must carry with you — civil twilight is when the sun's centre is between 0° and 6° below the horizon. That's the whole page. It's a reference table, so the skill is really in reading it accurately and understanding what the times mean for your flight planning.