Let me orient you — Page 451, Lesson 437

I want to walk you through a page from the General Navigation manual that looks like a wall of numbers at first glance, but it's actually one of the most practical tables you'll use as a pilot — the sunset table. Let me orient you. This is a tabulated listing of sunset times, arranged by latitude and by date. The latitudes run down the left-hand side — I can see S 30, S 52, S 60, and then N 72, N 70, N 68, N 66, N 64, N 62, N 60, and N 50. The "S" means South latitude, the "N" means North latitude. So this table covers both hemispheres. The columns across the top are dates. I can see the heading "SUNSET" and then "Lat." for latitude, followed by the months — August, September, October — and then a series of day numbers: 15, 18, 21, 24, 27, 30, then 2, 5, 8, 11, 14, 17, 20, 23, 26, 29, then 2 again. So the table gives you sunset times for specific dates through late August, all of September, and into early October. Now, the times themselves are given in hours and minutes — the "h" and "m" at the top of the columns stand for hours and minutes. So when you read a value like 21 43, that's 21 hours and 43 minutes — that's 9:43 PM in civil time, but in aviation we work in the 24-hour clock. Let me walk you through how to read one entry. Take the row for N 72 — that's 72 degrees North latitude, which is well inside the Arctic Circle. The first date column is August 15. The entry reads 21 43. So at 72 degrees North, the sun sets at 21:43 on the 15th of August. Then as you move across the row to later dates — August 18, 21, 24, 27, 30, and into September — the times get progressively earlier. 21 22, 21 03, 20 44, 20 27, 20 10, 19 53, 19 36, 19 20, 19 04, 18 49, 18 33, 18 18, 18 02, 17 47, 17 31, and finally 17 16. You can see the sun setting earlier and earlier as autumn approaches — that's the seasonal trend. Now look at the row for N 60 — 60 degrees North. The first entry is 19 55 on August 15, and it works its way down through 19 46, 19 38, 19 29, 19 20, 19 11, 19 02, 18 53, 18 44, 18 35, 18 26, 18 17, 18 08, 17 58, 17 47, 17 40, and 17 31. Compare that to N 72 — at 60 North the sun sets earlier in mid-August, 19:55 versus 21:43, because you're further from the pole and the days are shorter at that latitude in late summer. Now here's the key thing about how these tables are laid out. The main row gives you the time for the date at the top of the column. But the smaller numbers beneath each main entry — those are the daily increments. Let me show you. In the N 60 row, under the 19 55, there's a small 58. Then under 19 46 there's 46, under 19 38 there's 38, and so on. These small numbers tell you how much the sunset time changes from one day to the next — the daily rate of change in minutes. So the sun is setting earlier each day, and that small figure is the amount of that daily shift. Let me trace one column to make this concrete. Take the column for August 18. In the N 72 row, the main time is 21 22, and the small number beneath is 21. In the N 70 row, the time is 20 55 with a small 40. N 68 gives 20 35 with 22. N 66 gives 20 20 with 08. N 64 gives 20 06 with 56. N 62 gives 20 05 with 46. N 60 gives 19 46 with 46. And N 50 gives 19 14 with 45. So you can see the sunset time varies with latitude on the same date — the further north, the later the sunset in August. Now, why does this matter to you as a professional pilot? Sunset time is a legal and operational boundary. Many flight operations, particularly visual flight rules operations, have restrictions tied to sunset and sunrise. Night flying, the carriage of passengers, the need for certain equipment and lighting — all of these can hinge on whether you're operating before or after sunset. So this table lets you determine, for your latitude and your date, exactly when the sun goes down, so you can plan your flight to stay within the legal operating conditions. Let me also point out the structure of the table itself. The latitudes are grouped — I see S 30, then S 52, then S 60, then the N latitudes from N 72 down to N 50. Each latitude row has its own set of times across the date columns. The table is dense, but the logic is simple: pick your latitude, pick your date, and read the sunset time at the intersection. One more thing to notice — the times are not evenly spaced across latitudes. Look at the difference between N 72 and N 60 on August 15: 21:43 versus 19:55, a difference of nearly two hours. But between N 60 and N 50 on the same date: 19:55 versus 19:19, a difference of only 36 minutes. So the closer you get to the pole, the more dramatically the sunset time changes with latitude. That's the geometry of the Earth's tilt and the sun's path — and it's exactly why the table is broken out by latitude rather than giving you one set of times for everywhere. So when you use this table in practice, you'll interpolate. If you're at a latitude between two listed rows, or on a date between two listed columns, you estimate the sunset time between the surrounding values. The table gives you the anchor points, and you do the mental interpolation. That's the sunset table. It's a tool for determining the time of sunset at your latitude and date, which is a critical input for planning legal and safe flight operations.