First, let's orient you — Page 444, Lesson 416

I want to walk you through the sunset table in your General Navigation manual — this is the kind of data you'll be reading straight off the page in the exam and in the aircraft. First, let's orient you. This is a table of sunset times for latitudes in the Northern Hemisphere, arranged by month and by day of the month. The column on the far left is Latitude, in degrees North — you'll see N 72, N 70, N 68, N 66, N 64, N 62, N 60, N 58, N 56, N 54, N 52, and N 50. So the table covers from 72° North down to 50° North. Across the top, the months are April and May, and under each month the days are numbered — 2, 5, 8, 11, 14, 17, 20, 23, 26, 29 for April, and then 2, 5, 8, 11, 14, 17 for May in the part you can see. The times are given in hours and minutes — the little "h" and "m" at the top of the columns tell you that. Now, here's the key thing about how to read this table. The times are in Local Mean Time — that's the time based on the sun's position at your meridian, not your zone time. And the values are rounded to the nearest minute. So when you look up a sunset time, you're getting the minute the upper limb of the sun — the top edge of the sun's disc — crosses the horizon. Let me show you how to actually read a value. Take latitude N 60 and April 2. You read across the row for N 60 and down the column for April 2, and you get 18 hours 45 minutes — written as 18 45. So sunset at 60° North on April 2 is at 18:45 Local Mean Time. Now look at the pattern as you go up in latitude. At N 72 on April 2, sunset is at 19 hours 17 minutes — 19:17. At N 70 it's 19:09, at N 68 it's 19:03, at N 66 it's 18:57, at N 64 it's 18:53, at N 62 it's 18:49, and at N 60 it's 18:45. So the higher the latitude, the later the sunset in early April — the days are longer further north in spring. You'll also notice some entries are marked with a G — you see G against N 72, N 70, and N 68. That G is a flag in the table, and it's telling you something important about those particular values. When you see that G in the actual manual, it refers you to a note — and the note tells you that the time given is affected by refraction and the semi-diameter of the sun. In other words, the tabulated time is when the sun's upper limb appears to cross the horizon, not when the centre of the sun crosses it. That's a correction you need to be aware of when you're using these times for navigation. Let me also point out the S entries you'll see in the table — S 30, S 52, S 60. Those S markers indicate a change in the interval between successive tabulated values. When the table's compilers changed the step between rows or columns, they flagged it with an S so you know the spacing isn't uniform at that point. Now, one more thing about reading the times. Look at the values as they progress through the month. At N 60, April 2 is 18:45, and as you go to April 5, 8, 11, and so on, the times get later — 18:52, 19:00, 19:07, 19:14, 19:22, 19:29, 19:37, 19:44, 19:52, 19:59, 20:07, 20:14, 20:21, 20:28, 20:35. So through April, sunset at 60° North gets later by roughly 7 minutes every 3 days. That's the seasonal trend — the days are lengthening. And here's a practical point for you as a navigator. This table gives you sunset at Local Mean Time. To use it in flight, you have to convert that LMT to your zone time — the time you'd actually have on your clock — and you do that using your longitude. The relationship is that Local Mean Time differs from zone time by 4 minutes for every degree of longitude you are away from the zone meridian. So if you're east of the zone meridian, LMT is ahead of zone time; if you're west, it's behind. So the workflow is: look up your latitude and the date, read the sunset time in LMT, then apply the longitude correction to get the zone time of sunset for your position. That's how this table becomes a real navigation tool rather than just a page of numbers. Let me just make sure you've got the structure firmly. Latitude on the left, in degrees North. Month and day across the top. Times in hours and minutes of Local Mean Time, rounded to the nearest minute. The G flag means the value includes refraction and semi-diameter corrections. The S flag marks a change in the tabulation interval. And the higher the latitude, the later the sunset in April and May in the Northern Hemisphere. That's the sunset table. When you're ready, we can move on to the next part of the chapter.