Let me orient you — Page 451, Lesson 437

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 Sunset Table — a standard page from the Air Almanac that you'll use in General Navigation to work out times of sunset for any given latitude and date. Let me orient you. The table is arranged by latitude, running down the left-hand side in bands. You'll see latitude values like S 30, S 52, S 60, and then on the right-hand side you'll see N 72, N 70, N 68, N 66, N 64, N 62, N 60, N 50. The "S" stands for South latitude, the "N" for North latitude. So the table covers both hemispheres. Across the top, the columns are dates. You'll see August, then September, then October, with the day numbers running across: 15, 18, 21, 24, 27, 30, then 2, 5, 8, 11, 14, 17, 20, 23, 26, 29, then 2. So the table gives you sunset times for specific dates through late summer into autumn. Now, the key thing to understand is the format of the times. Look at the header row — it shows h and m, which stand for hours and minutes. The times are given in UTC, which is Universal Time Coordinated — the standard time reference used in aviation, sometimes called Zulu time. So when you read a value like 21 43, that means 21 hours and 43 minutes UTC. Let me show you how to read an actual entry. Take the top band, N 72 — that's 72 degrees North latitude. The first entry under August 15 is 21 43. That means at 72 degrees North, on August 15th, sunset occurs at 21 hours 43 minutes UTC. Then August 18th gives 21 22, August 21st gives 21 03, and so on. You can see the times getting progressively earlier as the dates advance into autumn — that's the seasonal shortening of daylight hours in the Northern Hemisphere. Now look at the S 30 band at the top left. The first entry is 06 34 — 6 hours 34 minutes UTC. Compare that with the N 72 entry of 21 43. The Southern Hemisphere times are in the morning hours, because when it's sunset in the south, it's a different time of day in UTC. And you'll notice the S 30 times are increasing as the dates progress — 06 34, 06 31, 06 28, 06 25 — getting later. That's the opposite trend from the north, because the Southern Hemisphere is heading into spring, with days lengthening. Let me trace one full row so you see the pattern clearly. Take N 60 — 60 degrees North. The row starts at 19 55 for August 15th, then 19 46, 19 38, 19 29, 19 20, 19 11, 19 02, then 18 53, 18 44, 18 35, 18 26, 18 17, 18 08, then 17 58, 17 47, 17 40, and finally 17 31. So over the course of about six weeks, sunset at 60 North shifts from just before 8 PM UTC to about 5:30 PM UTC. That's a drop of over two hours — a very noticeable shortening of the day at high latitude. Now, here's an important detail about how these tables are structured. You'll notice that within each latitude band, there are multiple rows of numbers, not just one. Look at the N 50 band at the bottom — the main row reads 19 19, 19 14, 19 08, 19 02, 18 56, 18 49, 18 43, 18 37, 18 30, 18 24, 18 17, 18 10, 18 04, 18 57, 17 51, 17 44, 17 38. But beneath that, there's a second row: 45, 19 07, and so on. These are interpolation values. The main row gives you the sunset time for the exact latitude listed — say, exactly 50 North. But if your position is between two listed latitudes — say, 51 North — you need to interpolate. The smaller numbers below give you the correction per degree of latitude to apply to the main time. Let me make that concrete. Suppose you're at 51 degrees North on a given date. You'd take the sunset time from the N 50 row, then add the correction shown in the sub-row — the value like 45 or 19 07 — to adjust for that one extra degree of latitude. The same principle applies throughout the table: the main entries are for the exact latitude, and the sub-entries let you adjust for positions between the printed latitudes. There's one more critical thing I need to flag, and it's a trap you must avoid. Look carefully at the N 60 band. You'll see an entry that reads 06 2 — that's a typographical error in the source, missing a digit. When you encounter something like that in a real table, you must interpolate — estimate the correct value from the surrounding entries — rather than using the corrupted number. This is exactly the kind of vigilance that's expected of a professional navigator. You don't blindly copy; you sanity-check against the trend of the row. Also note the SUNSET label at the top of the right-hand section — that confirms this entire table is for sunset times, as opposed to sunrise tables which would be a separate page. So, to summarise the skill: you identify your latitude band, you find your date column, you read the hours and minutes in UTC, and if you're between latitudes, you apply the interpolation correction from the sub-row. The times trend earlier in the Northern Hemisphere through August to October, and later in the Southern Hemisphere, reflecting the seasons. That's the complete picture of this page. When you're ready, we can move on to how this sunset time feeds into your actual navigation calculations — things like working out civil twilight or planning a night flight.