Let me first explain what you're looking at — Page 451, Lesson 436

I want to walk you through this table, because it's one of the most practical tools you'll use in general navigation — the sunrise table. This is the kind of data you'd find in the Air Almanac or a nautical almanac, and it lets you work out, for any given latitude and date, what time the sun comes up. Let me first explain what you're looking at. The table is laid out with latitude values down the left-hand side, and dates across the top. The dates run from August through to October, and you'll see they're broken into specific days — the 15th, 18th, 21st, 24th, 27th, and 30th of August, then the 2nd, 5th, 8th, 11th, 14th, 17th, 20th, 23rd, 26th, and 29th of September, and then the 2nd of October. So the columns are every third day, roughly. Now, the latitudes. They run from N 72 degrees at the top, all the way down through N 70, N 68, N 66, N 64, N 62, N 60, then N 58, N 56, N 54, N 52, N 50, then N 45, N 40, N 35, N 30, N 20, N 10, then the equator — that's the row marked just "0" — and then into the southern hemisphere: S 10, S 20, S 30, and S 35 at the bottom. Here's the key thing to understand about the numbers in the cells. Each entry is a time, given in hours and minutes — you'll see the format like "02 21" or "04 13". The first two digits are the hour, the next two are the minutes. So for N 72 degrees on the 15th of August, the sunrise is at 02:21. That's the local mean time of sunrise at that latitude on that date. Now, let's look at the pattern, because this is where the real navigation understanding comes in. Look at the top of the table, at the high northern latitudes. At N 72 degrees in mid-August, sunrise is at 02:21. As the dates progress through August and into September, you'll see the times getting later — 02:41, 02:59, 03:17, 03:33, 03:49, 04:04, 04:18, 04:33, 04:47, 05:00, 05:14, 05:27, 05:41, 05:54, 06:08, and finally 06:21 by the 2nd of October. So at high northern latitudes, sunrise is getting later and later as autumn approaches — the days are shortening. Now compare that with what happens near the equator. Look at the row for N 10 degrees. The times there barely change at all — 05:51, 05:51, 05:51, 05:51, 05:51, 05:51, 05:51, 05:51, 05:50, 05:50, 05:50, 05:50, 05:49, 05:49, 05:49, 05:49, 05:49. The variation is only a couple of minutes across the whole period. That's because near the equator, day length is almost constant throughout the year. And then look at the southern hemisphere rows. At S 30 degrees, the sunrise times are getting earlier as the dates progress — 06:34 on the 15th of August, coming down to 05:38 by the 2nd of October. That's because in the southern hemisphere, spring is approaching, so the days are lengthening and the sun is coming up earlier. So the whole table is really showing you the seasonal progression of sunrise times as a function of latitude. The further you are from the equator, the more pronounced the change is. At N 72, the change across this period is about four hours. At the equator, it's almost nothing. And the sign of the change flips when you cross into the southern hemisphere. Now, one thing I want to point out about the structure of the table, because it's easy to misread. The latitude values are given in the left-hand column, but you'll notice some rows have the latitude label only at the start, and then the row continues with just the time values. For example, the row for N 60 has its label at the left, and then the times run across. But some rows are split — you'll see the latitude label appears again partway down, like "N 50" appears, and then later "N 45", "N 40", "N 35", "N 30", "N 20", "N 10". So each horizontal band of times corresponds to the latitude shown at its left edge. There's also a subtlety in how the minutes are sometimes written. You'll see entries like "04 04" followed by "17" — that's shorthand. The "17" means 04:17, continuing the same hour. So when you see a two-digit number alone in a cell, it's the minutes, and the hour carries over from the previous entry. For example, in the N 70 row: 02:54, 03:09, 03:23, then "38" which means 03:38, then "51" meaning 03:51, then 04:04, then "17" meaning 04:17, and so on. You have to keep track of the hour as you read across. Let me give you a concrete example of how you'd actually use this. Say you're planning a flight and you need to know when the sun rises at N 50 degrees latitude on the 20th of September. You find the N 50 row, you find the column for September 20th, and you read the time. In this table, that entry is 05:33. So sunrise at N 50 on the 20th of September is at 05:33 local mean time. Now, a word of caution about what this table does not tell you. This is sunrise time only — it's not giving you sunset, and it's not giving you the duration of daylight. To get day length, you'd need the corresponding sunset table and you'd work out the difference. Also, these times are local mean time, not standard zone time — so if you're working in a time zone, you'd need to apply the longitude correction to convert from local mean time to zone time. That's a separate step in the navigation process. One more thing to notice: the table only covers August through October. That's because this is an excerpt — the full almanac would have tables for the entire year, month by month. The principle is exactly the same for every month; only the numbers change. So to summarise what you should take away from this: the sunrise table gives you local mean time of sunrise for a given latitude and date. High latitudes show large seasonal variation, the equator shows almost none, and the southern hemisphere shows the opposite trend to the north. When you read the table, watch the hour carry-over in the minute-only entries, and remember these are local mean times, not zone times. That's the core of how this tool works.