Yes, the tip of a shadow does NOT in general form an east-west line. (I guess it’s a good lesson in how 95% of 'how-to’s on the internet are just copies of the same, possibly mistaken, thing).
You CAN find E-W from shadows, by connecting the tips of two shadows, but the shadows have to be from exactly the same amount of time before noon and after noon. Conveniently, the shadows will also be the exact same length at those two times.
So, in the morning mark the tip of a shadow from a vertical stick, draw a circle around the stick with the same length as the shadow at that point (so the tip of the shadow is on the circle). Now wait as the shadow shortens (before noon) then lengthens (after noon). When the tip of the shadow hits the circle again (on the east side this time), mark that point. A line through the two points will be exactly east-west. This is much easier and more accurate if you have a length of string (for drawing the circle and for plumbing the stick to be vertical).
I imagine this would be more accurate than finding north by star rotation, but it would require waiting until sunset instead of sunrise to make the call (and of course won’t work if it gets cloudy during the day). Not sure if the extra accuracy is really worth waiting 12 hours.
You know, when I read that, it seemed wrong to me, so I did a quick Google search for shadow compasses and found a number of videos of people showing the shadows tracing out a straight line. This still seemed so wrong to me that I actually have a stick out in the yard right now, and it confirmed my belief that the shadow tip will trace an arc. So now the question is whether these videos were purposefully filmed on the equinox without mentioning it, OR whether they were filmed over a short period of time near sunup or sundown, when the arc is flattest and the curvature isn’t easily detected. One guy did have a video where he compared his ‘n-s’ line to a magnetic compass and it was off by probably 20+ degrees, which he attributed to magnetic declination. Which made me wonder where in the world there could be such a severe mismatch (far southern New Zealand or far northern Russia, as it turns out, but he wasn’t in either of those places). He probably wasn’t trying to fool anybody by shooting on the equinox.
Noon is still the point at which the shadow is shortest - where the shadow arc is closest to the shadow-caster - and the angular height of the Sun at noon will let someone with the proper tables look up your latitude.
In the interest of full disclosure, I had a full post typed out about how you could tell if you were in the N or S hemisphere by whether the sun went around in the northern or southern half of the sky, forgetting about the whole band between the tropics. A few minutes on The Photographer’s Ephemeris helped me out there.
Well yeah, I realize that, but do you think it would be enough curvature to matter? If you’re not at extreme latitude and you’re not near the solstices, it shouldn’t be enough of an arc to make a difference in the overall escape plan, I wouldn’t think. If you take measurements, say, 3 times at 2 hours apart, the arc is essentially removed, right?
Perhaps I’m wrong and the arc is more pronounced than I give it credit for. Still, we’re only using it to orient ourselves, not to calculate any precise coordinates, so that I can convey the island’s shape via the chess board description. What am I missing?
You would literally get a better estimate of north just by defining the direction of sunrise as “east”, than by measuring the shadow-line near sunrise. You could do well with your method if it’s near noon, but that depends on determining noon.
But wouldn’t that also suffer the same error if used at extreme latitude? IIRC, the sun rises much further south of east if you’re far north than if you’re in the tropics, yes?
Any significance to the fact it was a snowy night when you were abducted but it’s only cool, but not cold on your deserted island? And that you know the direction the kidnappers left in?
I think it may be significant that it’s a treeless island. Can’t use wood/sticks to help determine your latitude with a rudimentary sextant. That would also make it hard to determine noon with out being able to get a reasonably tall shadow.
Why it’s included that it’s a treeless island may be significant. Where would one find a treeless island in a moderate climate?
Odd that salt water is brought up too. Seems sort of like a ‘DUH’. But something may be there.
Take a look at The Photographer’s Ephemerisand play around with the slider on the blue bar at the bottom of the screen. There’s a tutorial video herethat explains what you are seeing as you slide the time around. It shows a representation of how a shadow moves and changes length over the course of a day as a thick dark brown line: yes, the arc can be quite pronounced.
At my current location, for today’s date, if I plotted the shadow near dawn and one hour later, the resulting line would run almost 45 degrees off the true E-W line. The shadow for today swept around 245 degrees, starting in the SW, swinging to the north, and then to the SE at sunset.
Ah, but the night is cool and the sky is clear, where you were taken from I would suspect cold and overcast with the snowiness.
The horizon the maybe mothership lights twinkled off from would have been maybe three miles off. That’s quite the detour.
I’m on a nice temperate sandbar/island, a ways from home, in cold weather clothing(less footware) where biolument life resides in the tide. Why can’t I call till dawn?
I think both of these are to establish that the time of year (and island location) allow for using sunrise and sunset to get approximate locations. It being a snowy night when abducted implies winter (so you’re not around the equinoxes where it might make things more difficult), while the island being cool implies that you’re away from the equator (maybe even outside the tropics), again allowing for the timing of sunrise and sunset in order to establish approximate location.
Yeah, calling the direction of sunrise “east” isn’t very accurate, either, but it’s still better than the arc of the shadow. If you’re not near the poles (and you’re not; this island is comfortable in bare feet even while your hometown is snowy) it’s probably good enough for a rough description of the shape of the island, but for any navigation-related purposes, you’ll want to do better.
I have to wonder if we can get anything useful from the extent of the tides, but for a nearly-flat sand island out of sight of any other land, it’s probably redundant with the other information we have.
I mentioned tides early on, but this is an assumption that we are in the ocean. It could be a large salt lake. Some of the clues are ambiguous like that…the light in the distance isn’t necessarily an ocean ship; the light surf is more lake like than ocean. The small flat sand island indicates shallow water rather than deep ocean.
Simply the lack of tides would indicate a lake and be useful information.
Except that tides are fairly small, in the open ocean, and there are other phenomena in lakes that could be mistaken for tides. And there are precious few salt lakes big enough that you could put an island in them out of sight of any other land, and most salt lakes are easily distinguished from the ocean by virtue of being much saltier.
I do appreciate your comments about the lack of salt lakes being that big, but there might be some.
Also the thought that tides are small in the ‘open ocean’ is not totally accurate in this case, since it isn’t strictly ‘open ocean’ with shallow enough water to support a sand island. I don’t know enough about tides to know if small sandy islands will have large enough discernible tides or not. I just assumed they did.
One assumption that everyone seems to be making, which I don’t think is a safe one, is that whoever you call is (a) available and (b) going to answer quickly. If you call someone and it rings six times and then goes to voicemail, you’re going to be out of battery before you have a chance to say anything.
There is the concern that a flat sandy island like that is not permanent and not found on maps. My limited knowledge tells me that’s an island like that is more common in the ocean than a lake, but I have no idea what the Caspian Sea or other salt lakes are like.