Quote:
Originally Posted by Nathaniel B.
Let's take a look at the case you cited as a "check":
Many times, it is useful to look at an extreme example of a situation to understand the mechanics behind it. So, let's assume we are almost at the North Pole...our latitude is 89°59'59"N. Only one arc second away from the pole itself. Our longitude is 0°00'00"E. We are on the Greenwich meridian and therefore our local time is exactly equal to UTC. The date is September 6th, 2017 and the time is 07:30 UTC. The Moon is full (as full as it will get at this time at 99.9% illumination). Now, what is the Moon's altitude? If you click on Fig. 1, you will see that it is at 8°54'21" below the horizon (represented by the green circle).
Next, we wait six hours until 13:03 UTC. Now what is the Moon's altitude? Fig. 2 shows that it is still 7°53'18" below the horizon. Another six hours later at 19:03 UTC and Fig. 3 shows that the Moon is still 6°50'38" below the horizon. So what time will it rise? Well, the bottom left corner of Fig. 3 gives away the fact that the Moon will not rise at all on this date, at this location. In fact it won't rise until two days later, on September 8th, at which point it won't set again until September 20th...another twelve days away.
Suppose our latitude was 45°00'00"N (still on the Greenwich meridian, back on September 6th). Now what time will the moon rise? Fig. 4 shows that it already rose at 18:22 UTC the previous day. And if we were almost at the South Pole...what then? Fig. 5 shows that the Moon never rose on this day. At this latitude and time it is "circumpolar", meaning it stays above the horizon all day.
So, "what time MUST the full moon rise?" The answer is: it depends. But, on what? ... If you answered "the observer's latitude", congratulations! You are correct...partially. Unlike the Sun, the Moon is revolving around the Earth as the Earth itself rotates. The speed of the Moon's revolution is great enough that, the farther away from Greenwich you are, the more the time of Moon rise/set changes from what is listed in the Nautical Almanac.
That is why there is a " Table for Interpolating Sunrise, Moonrise, Etc." included in the N.A. This table allows for the adjusting of sunrise/set times for latitude and Moon rise/set times for both latitude and longitude.Because these are two of the primary factors which govern what time the phenomena occur for a given observer.
As I said: I have spent years intensely studying celestial navigation. I'm not just speaking from some cursory understanding of the subject. I own several sextants and have taken hundreds of sights, including " lunars". I have even generated my own "Time Sight Logarithm Tables" which can be used to navigate the way sailors did back in the 19th century. You may have noticed that my forum nickname is actually the name of the author [or editor, more precisely] of one of the most famous American books on navigation at sea: Nathaniel Bowditch...author of The American Practical Navigator, otherwise known simply as Bowditch.
Anyway, I hope all of that was clear enough. And I hope to be able to help DaveR with his problem...although from my initial calculations, it seems that SH might actually have some inaccuracies. I'll need to investigate further and get the answers to my questions to really know. We'll see. |
The answer is that the full moon MUST be 180 degrees opposite the sun. Therefore, if the sun sets at 6:30 pm, the full moon MUST rise at that time. Now we can muddy our thinking by placing ourselves in a place where the sun doesn't set (therefore the full moon would never rise), but just like Einstein's Theories of Relativity and Newtonian Physics, that doesn't invalidate the general rule, it merely clarifies it for extreme situations.
That brings up a really cool situation north of the arctic circle, where in winter, the sun never rises. The full moon, opposite the sun, therefore never sets. You can wake up in the "morning" and see the full moon just run a full circle in the sky for the day. If you're at the pole, the moon's altitude won't change. If you're between the pole and the arctic circle, the moon will incline to the horizon in its circle through the sky at an angle of 90 minus your latitude to the horizontal, but never set. It just appears to orbit you with a period of 24 hours!
Our situation in the game is in the tropics, VERY typical. But even on the north pole, the full moon is found 180 degrees from the Sun. It's interesting that any farmer from 1850 knew more about lunar phases than we do. They would rightly laugh at the proposition that the full moon can rise at any time.
Show me any time in history between plus and minus 45 degrees latitude where the full moon rose at midnight. It can't happen. Two hours before or after sunset. It can't happen. It's a simple mechanical relationship. And don't change the definition of full. Full is 100% illumination, not 99.7%, not 99.9%. The moon moves away from the Sun at about 11 degrees a day. 11 degrees is about 50 minutes time. So a NEARLY full moon naturally changes its rise and set time. The moon, 24 hours after 100% full, rises 50 minutes earlier than it did the previous day! (15º = 1 hour) Changing the terms and claiming that you have somehow invalidated another situation altogether is called a paper tiger argument. We have to use the same terms or there's no effect.
Quote:
|
Although Full Moon occurs each month at a specific date and time, the Moon's disk may appear to be full for several nights in a row if it is clear. This is because the percentage of the Moon's disk that appears illuminated changes very slowly around the time of Full Moon (also around New Moon, but the Moon is not visible at all then). The Moon may appear 100% illuminated only on the night closest to the time of exact Full Moon, but on the night before and night after will appear 97-99% illuminated; most people would not notice the difference. Even two days from Full Moon the Moon's disk is 93-97% illuminated.
|
US Naval Observatory
Unfortunately, Silent Hunter 4 renders the earth as a cylinder with diameter who knows and a height of the linear distance from pole to pole. Therefore there is no difference in sunrise and sunset with latitude anyway. That alone completely invalidates celestial navigation, which incorporates 3 dimensional trigonometry to fix the ground point of stars and planets. You can't do that on a cylinder. Unfortunately, the ground "point" of any celestial object is a vertical line extending from pole to pole, approximately 12,430 statute miles long! The whole shebang falls flat on its face.
Reality ALWAYS trumps math. Unfortunately, due to a recent act of Congress, reality exists in the computer and we occupy virtual reality!
Oh, my photos link to Google Photos. I'll post a link to the photo in question and lets see if you can get there indirectly:
https://photos.app.goo.gl/27C6mQ3TeNue8BO73
Usually I run it through Google IRL shortener,
goo.gl, and post THAT link, but let's try the raw link from hell here and see if you can see it.
Nathaniel, you're a perfect example to show that people can disagree without being disagreeable. It's a pleasure to swap ideas with you.