Reply
 
Thread Tools Display Modes
  #51  
Old 06-10-2019, 09:40 PM
silenus's Avatar
silenus is offline
Isaiah 1:15/Screw the NRA
Charter Member
 
Join Date: May 2003
Location: SoCal
Posts: 51,356
Quote:
Originally Posted by Chessic Sense View Post
I was just hit with some inspiration. How about manufacturing an astrolabe out of the water bottle?

Guy Fleegman: I know! You construct a weapon. Look around you. Can you form some sort of rudimentary lathe?
  #52  
Old 06-10-2019, 11:03 PM
brossa is online now
Guest
 
Join Date: Feb 2005
Posts: 1,141
It would probably be of value to do a seconds count to see how long it takes the Sun to rise completely, from first sighting to fully above the horizon. Say this is 200 seconds. So now you know that when the sun is setting, from the time it grazes the horizon until it vanishes completely will also be about 200 seconds. This lets you time your phone call so that it will overlap that vanishing point; once you think the Sun is touching the horizon, wait 170 seconds and place your call. It's easier to say when the Sun has disappeared than to say with certainty when it is 100% risen. The Sun takes from 2 to 5 minutes to rise and set depending on latitude and time of year, and it would be a waste to place your phone call too soon or late to capture the moment of disappearance.
  #53  
Old 06-10-2019, 11:21 PM
brossa is online now
Guest
 
Join Date: Feb 2005
Posts: 1,141
Also, the folded paper bag will give you a 90 degree corner to help determine the point on your E-W shadow line that is closest to your shadow tower. That's the noon point, and the ratio of tower height over shadow length at that point will help the rescuers find your latitude.
  #54  
Old 06-11-2019, 02:45 AM
TokyoBayer's Avatar
TokyoBayer is online now
Guest
 
Join Date: Oct 2003
Location: Taiwan
Posts: 10,498
After you drink the first bottle of water, fill with sea water and turn it upside down.

If the draining water rotates clockwise, you are in the northern hemisphere. If it rotates counterclockwise, you are in the Southern Hemisphere.

If it can’t drain because the water can’t decide which way to rotate, you are either exactly in the equator to within feet, or you are starring in the Truman Show.
  #55  
Old 06-11-2019, 05:38 AM
Isosleepy's Avatar
Isosleepy is online now
Charter Member
 
Join Date: Jul 1999
Location: Pittsburgh
Posts: 1,636
We are all assuming the goal is to be rescued without paying the ransom. But per the riddle, we are “super rich”. Maybe the solution is to wait for dawn, call our people and tell them to pay the fucking ransom.
  #56  
Old 06-11-2019, 05:42 AM
N9IWP is offline
Charter Member
 
Join Date: Aug 2001
Location: Southeast MN
Posts: 6,273
I hope that was a joke, as the Coriolis force is VERY weak on something on that scale

Brian
  #57  
Old 06-11-2019, 07:45 AM
brossa is online now
Guest
 
Join Date: Feb 2005
Posts: 1,141
Actually, that folded paper bag might work as a astrolabe too. Hold one corner toward your eye, with the adjacent 90 degree corner away from you. Holding your head still, manipulate the bag until you are sighting along the bottom edge at the horizon just below the Sun. Now mark the height of the Sun along the far vertical edge of the bag. Do this multiple times, and eventually the Sun won't be climbing any more; the highest mark indicates the greatest height of the Sun, and you can draw the angle on the bag.
  #58  
Old 06-11-2019, 08:31 AM
Quercus is offline
Guest
 
Join Date: Dec 2000
Location: temperate forest
Posts: 7,121
Quote:
Originally Posted by brossa View Post
It would probably be of value to do a seconds count to see how long it takes the Sun to rise completely, from first sighting to fully above the horizon. Say this is 200 seconds. So now you know that when the sun is setting, from the time it grazes the horizon until it vanishes completely will also be about 200 seconds. This lets you time your phone call so that it will overlap that vanishing point; once you think the Sun is touching the horizon, wait 170 seconds and place your call. It's easier to say when the Sun has disappeared than to say with certainty when it is 100% risen. The Sun takes from 2 to 5 minutes to rise and set depending on latitude and time of year, and it would be a waste to place your phone call too soon or late to capture the moment of disappearance.
I don't think we need that much accuracy. If we're off by one minute for the sunrise time, that's a maximum error of 16 miles or so (less away from the equator). Since the island is the only possible correct location within multiple miles, it wouldn't take long to correct that kind of error.
  #59  
Old 06-11-2019, 09:15 AM
Chronos's Avatar
Chronos is offline
Charter Member
Moderator
 
Join Date: Jan 2000
Location: The Land of Cleves
Posts: 84,384
Quote:
Quoth Chessic Sense:

You don't need to estimate the length of a shadow to find noon. You plant an object with an obvious tip in the sand, standing vertically. A water bottle will do. At some point in the day, at any time, you mark the shadow's tip with any object. Another water bottle will work, especially if laid on its side, but I'd prefer a seashell or pebble.

Then you wait at least 15 minutes, but preferably several hours. You then mark the tip again. Connect the two marks with a line. Wait a few hours more and verify with a third point.

This line is a direct east/west line. It's not an arc.
The reason nobody suggested that is because it only works at the equinox. At any other time of year, that line will indeed curve. If I were to do it today, for instance, at noon the shadow would be north of the gnomon, and at sunrise and sunset, the shadow would be south of the gnomon. It's tough to make a straight line do that.
  #60  
Old 06-11-2019, 09:20 AM
Saffer is offline
Guest
 
Join Date: Feb 2009
Posts: 385
Quote:
Originally Posted by TokyoBayer View Post
After you drink the first bottle of water, fill with sea water and turn it upside down.

If the draining water rotates clockwise, you are in the northern hemisphere. If it rotates counterclockwise, you are in the Southern Hemisphere.

If it can’t drain because the water can’t decide which way to rotate, you are either exactly in the equator to within feet, or you are starring in the Truman Show.


I feel the need to point out how absurd this post is; the Truman show isn’t a real thing.


Sent from my iPhone using Tapatalk
  #61  
Old 06-11-2019, 10:57 AM
Quercus is offline
Guest
 
Join Date: Dec 2000
Location: temperate forest
Posts: 7,121
Quote:
Originally Posted by Chronos View Post
The reason nobody suggested that is because it only works at the equinox. At any other time of year, that line will indeed curve. If I were to do it today, for instance, at noon the shadow would be north of the gnomon, and at sunrise and sunset, the shadow would be south of the gnomon. It's tough to make a straight line do that.
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.
  #62  
Old 06-11-2019, 04:03 PM
brossa is online now
Guest
 
Join Date: Feb 2005
Posts: 1,141
Quote:
Originally Posted by Chronos View Post
The reason nobody suggested that is because it only works at the equinox. At any other time of year, that line will indeed curve. If I were to do it today, for instance, at noon the shadow would be north of the gnomon, and at sunrise and sunset, the shadow would be south of the gnomon. It's tough to make a straight line do that.
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.
  #63  
Old 06-11-2019, 08:03 PM
Chessic Sense is offline
Guest
 
Join Date: Apr 2007
Posts: 6,739
Quote:
Originally Posted by Chronos View Post
The reason nobody suggested that is because it only works at the equinox. At any other time of year, that line will indeed curve. If I were to do it today, for instance, at noon the shadow would be north of the gnomon, and at sunrise and sunset, the shadow would be south of the gnomon. It's tough to make a straight line do that.
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?

Last edited by Chessic Sense; 06-11-2019 at 08:05 PM.
  #64  
Old 06-11-2019, 08:25 PM
Chronos's Avatar
Chronos is offline
Charter Member
Moderator
 
Join Date: Jan 2000
Location: The Land of Cleves
Posts: 84,384
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.
  #65  
Old 06-11-2019, 08:51 PM
dtilque is online now
Charter Member
 
Join Date: Jan 2000
Location: My own private Nogero
Posts: 6,968
Quote:
Originally Posted by Saffer View Post
I feel the need to point out how absurd this post is; the Truman show isn’t a real thing.
It is if you're in the Matrix.
  #66  
Old 06-11-2019, 09:15 PM
Chessic Sense is offline
Guest
 
Join Date: Apr 2007
Posts: 6,739
Quote:
Originally Posted by Chronos View Post
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?
  #67  
Old 06-11-2019, 09:23 PM
K2500 is offline
Guest
 
Join Date: Sep 2016
Posts: 529
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?

Last edited by K2500; 06-11-2019 at 09:27 PM.
  #68  
Old 06-11-2019, 10:38 PM
TokyoBayer's Avatar
TokyoBayer is online now
Guest
 
Join Date: Oct 2003
Location: Taiwan
Posts: 10,498
Quote:
Originally Posted by K2500 View Post
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?
The last probably not, as the kidnappers could be deliberately in the opposite direction just to throw you off.

It is significant that the nights are cool and not hot, as that should place you not on the equator.
  #69  
Old 06-11-2019, 11:01 PM
enipla is offline
Member
 
Join Date: Jul 2001
Location: Colorado Rockies.
Posts: 14,415
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.
__________________
I don't live in the middle of nowhere, but I can see it from here.
  #70  
Old 06-11-2019, 11:09 PM
brossa is online now
Guest
 
Join Date: Feb 2005
Posts: 1,141
Quote:
Originally Posted by Chessic Sense View Post
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?
Take a look at The Photographer's Ephemeris and play around with the slider on the blue bar at the bottom of the screen. There's a tutorial video here that 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.
  #71  
Old 06-11-2019, 11:24 PM
K2500 is offline
Guest
 
Join Date: Sep 2016
Posts: 529
Quote:
Originally Posted by TokyoBayer View Post
The last probably not, as the kidnappers could be deliberately in the opposite direction just to throw you off.

It is significant that the nights are cool and not hot, as that should place you not on the equator.
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?
  #72  
Old 06-12-2019, 07:03 AM
carlb is offline
Member
 
Join Date: Dec 2004
Location: Palmetto Bay, FL
Posts: 1,213
Quote:
Originally Posted by K2500 View Post
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 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.
  #73  
Old 06-12-2019, 07:50 AM
Chronos's Avatar
Chronos is offline
Charter Member
Moderator
 
Join Date: Jan 2000
Location: The Land of Cleves
Posts: 84,384
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.
  #74  
Old 06-12-2019, 08:05 AM
Sigene is offline
Charter Member
 
Join Date: Aug 2000
Posts: 2,361
Quote:
Originally Posted by Chronos View Post
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.
  #75  
Old 06-12-2019, 08:31 AM
Chronos's Avatar
Chronos is offline
Charter Member
Moderator
 
Join Date: Jan 2000
Location: The Land of Cleves
Posts: 84,384
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.
  #76  
Old 06-12-2019, 09:23 AM
MrDibble's Avatar
MrDibble is offline
Guest
 
Join Date: Mar 2001
Location: Cape Town, South Africa &
Posts: 25,858
We don't know how salty the water is, we only know it's salt.

And the Salton Sea does have some lovely bioluminescence...

On the other hand, there's no large islands in it...
  #77  
Old 06-12-2019, 10:13 AM
Sigene is offline
Charter Member
 
Join Date: Aug 2000
Posts: 2,361
Quote:
Originally Posted by Chronos View Post
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.
  #78  
Old 06-12-2019, 11:52 AM
MrDibble's Avatar
MrDibble is offline
Guest
 
Join Date: Mar 2001
Location: Cape Town, South Africa &
Posts: 25,858
Quote:
Originally Posted by Sigene View Post
it isn't strictly 'open ocean' with shallow enough water to support a sand island.
Eh? Do you think ocean islands can't have sand? Plenty that do. Here's one.
  #79  
Old 06-12-2019, 12:50 PM
Shoeless's Avatar
Shoeless is offline
Charter Member
 
Join Date: Jan 2003
Location: The Sunflower State
Posts: 6,717
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.

Other than that, I got nothin'.
  #80  
Old 06-12-2019, 01:05 PM
TriPolar is offline
Guest
 
Join Date: Oct 2007
Location: rhode island
Posts: 40,372
Quote:
Originally Posted by MrDibble View Post
Eh? Do you think ocean islands can't have sand? Plenty that do. Here's one.
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.
  #81  
Old 06-12-2019, 01:08 PM
BillGates is offline
Guest
 
Join Date: Jan 2018
Posts: 3
Strangely, there's no mention of the kidnappers leaving behind a way to contact them, so even if a ransom was arranged, how would they know (when) to come back and rescue you? Theoretically they could somehow reach out to every person you know that you might make your call(s) to, but that doesn't seem reasonable or likely.

Last edited by BillGates; 06-12-2019 at 01:10 PM.
  #82  
Old 06-12-2019, 01:16 PM
TriPolar is offline
Guest
 
Join Date: Oct 2007
Location: rhode island
Posts: 40,372
Quote:
Originally Posted by BillGates View Post
Strangely, there's no mention of the kidnappers leaving behind a way to contact them, so even if a ransom was arranged, how would they know (when) to come back and rescue you? Theoretically they could somehow reach out to every person you know that you might make your call(s) to, but that doesn't seem reasonable or likely.
I assume if the ransom is paid they'll reveal your location, maybe.
  #83  
Old 06-12-2019, 01:18 PM
Chronos's Avatar
Chronos is offline
Charter Member
Moderator
 
Join Date: Jan 2000
Location: The Land of Cleves
Posts: 84,384
Presumably the kidnappers know who your next of kin is, and have contacted them separately. And if you call any of "your people" to tell them you want them to ransom you, they'll spread the word. You're not the one paying the ransom, so you don't need to know how to contact the kidnappers.
  #84  
Old 06-12-2019, 03:37 PM
Sigene is offline
Charter Member
 
Join Date: Aug 2000
Posts: 2,361
Quote:
Originally Posted by MrDibble View Post
Eh? Do you think ocean islands can't have sand? Plenty that do. Here's one.
My apologies, I wasn't clear. The riddler indicates that the island is "all flat sand", no rock, no coral, no caves etc. like assumption island. So, Yes, I'm confident ocean islands can have sandy beaches, but that isn't what is described in the text.

My point is that an "all flat sand" island would not likely be in deep ocean but rather in fairly shallow water. Therefore, if it is in shallow water, I assumed, if in the ocean, it would have significant tides.

Again my knowledge of tides in shallow areas of the ocean where sand islands could exist is not strong, but I assume they would have noticeable tides.
  #85  
Old 06-12-2019, 03:52 PM
Quercus is offline
Guest
 
Join Date: Dec 2000
Location: temperate forest
Posts: 7,121
If you need to call in the morning (as the puzzle sort-of implies), then what's wrong with finding rough North by the movement of the stars, along with a rough latitude from the elevation of the center of movement; and calling at Sunrise to get a pretty good longitude, along with another rough latitude from the direction of sunrise?

In general, I'd consider calling at sundown instead, mostly so I could look around and see if there are any other islands visible, but also to get a more accurate latitude (mostly by getting a good east-west line from shadows, which will allow a more accurate bearing on sunset).

But even with the morning call, my rough estimate is that the longitude will be within 10 miles or so, and the latitude probably a couple hundred. Which, given that the search is for a clearly visible island, should be good enough, right?
  #86  
Old 06-12-2019, 05:53 PM
excavating (for a mind) is offline
Guest
 
Join Date: Nov 2010
Location: In a canyon, in a cavern
Posts: 1,528
A few things I find curious about the initial conditions.

Your "host" supplies you with four sandwiches and 4 pints of water, which is "enough for a few days." Now, most references I find on-line say a person will die in a few days without water, and that a person should expect to need at least two quarts per day, more in hot conditions. Now, you are on a desert island with no shade. The night sky is clear, which would suggest that you will have a cloudless day. I would expect a person exposed to the sun all day to need every bit of those 4 pints the first day. He might be able to survive on two pints per day, but he wouldn't be in very good condition after two days. To me, "a few days" suggests at least three, perhaps four, days. Lack of any vegetation on the island strongly suggests that there is no fresh water available.

As has been mentioned, the restriction on not calling "before daylight" is strange. My guess is this restriction is a hint, but perhaps it is merely obfuscation.

The sandwiches are interesting. Liverwurst and peanut butter on Rye. Another hint, or just obfuscation? Sure, liverwurst and peanut butter will have high protein and calorie, but if it's just a few days, it really wouldn't make that much difference if it was watercress and tomato. As mentioned, water is the big problem. A few days without food will make you very hungry, but it won't kill you (like a day without water in the sun can).

Waving at the surf and saying "that's salt" is also odd. One would expect salt water if the island was on an ocean, and it is easy to determine (which the marooned man does, in fact, do), so why does the kidnapper mention it?

I would imagine that "Your knowledge of astronomy is too weak to try to estimate your location by the stars" means that even locating Polaris is not in your skill set. That is, the intended solution does not involve looking at the stars.

The exactly one minute restriction on the battery is a bit strange. I understand it is a common device to limit phone use, but in real life, I don't think you could get that kind of accuracy in the amount of time on the phone.

Finally, without knowing east from west, north from south, before daybreak you have figured out what to do. The only suggestion made in this thread that seems to work for me is to call right at sunrise and tell them that you are on a desert island, the size of the island, that the sun is rising right now, and you will call again when the sun sets. Yes, this wouldn't work well close to an equinox, but the starting conditions seem to rule that out to begin with..
  #87  
Old 06-12-2019, 09:08 PM
Sigene is offline
Charter Member
 
Join Date: Aug 2000
Posts: 2,361
I also note that there is no "requirement" that the call is made on the first daybreak. This is just an assumption that 'at daybreak' means the first one. I wonder if there is advantage to wait an entire day, to get more information like the altitude of the sun at noon, and make the call on the next daybreak.

Last edited by Sigene; 06-12-2019 at 09:09 PM.
  #88  
Old 06-12-2019, 09:29 PM
dtilque is online now
Charter Member
 
Join Date: Jan 2000
Location: My own private Nogero
Posts: 6,968
Quote:
Originally Posted by Sigene View Post
My point is that an "all flat sand" island would not likely be in deep ocean but rather in fairly shallow water.
You're right. An island as described in the puzzle will be somewhere near a large land mass. Out in the open ocean, wind and waves (especially storms) will wash such an island away. Near continents and large islands, waves wash the sand down the coast in one direction. That means they will bring about as much sand to the island as they take away, so such islands are stable. (This is ignoring man-made structures such as jetties, which interfere with the natural movement of sand.)
  #89  
Old 06-13-2019, 03:44 AM
MrDibble's Avatar
MrDibble is offline
Guest
 
Join Date: Mar 2001
Location: Cape Town, South Africa &
Posts: 25,858
I read that as "all flat sand" as a covering as opposed to plants, but I see what you're saying.
  #90  
Old 06-14-2019, 07:35 AM
N9IWP is offline
Charter Member
 
Join Date: Aug 2001
Location: Southeast MN
Posts: 6,273
So my solution was correct:
https://fivethirtyeight.com/features...walk-to-class/

Specifically mentioned that is WASN"T equinox season
Brian
  #91  
Old 06-14-2019, 12:44 PM
brossa is online now
Guest
 
Join Date: Feb 2005
Posts: 1,141
I will argue that you can't determine hemisphere by whether the shadow is to the north or south of the bottle; instead you can determine whether you are north or south of whichever latitude line has the noon sun directly overhead for that date. There may be a more elegant way of putting that. This line of latitude varies from the Tropic of Capricorn to the Tropic of Cancer depending on the date. So, on June 21st (summer solstice) if the shadow at noon is pointing south, the most that you can say is that your latitude is somewhere between ~23.5 deg North, and 66.5 deg South (any further South on that date and the Sun wouldn't ever rise). But on December 22nd, if the noon shadow was pointing South, you would say that you were between ~23.5 deg South and 66.5 deg S (again, any farther South and the Sun wouldn't have ever set).

Those of us who live in the mid- or- high-latitudes get used to the Sun always moving across the same half of the sky, year-round. But in the Tropics, sometimes it's in the North and sometimes it's in the South.

Further quibble: there's nothing in the original question to prove that it isn't near the equinoxes; there are plenty of places in the world where it could be snowy around the vernal or autumnal equinoxes. Youtube example.

Last edited by brossa; 06-14-2019 at 12:45 PM.
  #92  
Old 06-15-2019, 12:16 AM
TokyoBayer's Avatar
TokyoBayer is online now
Guest
 
Join Date: Oct 2003
Location: Taiwan
Posts: 10,498
Quote:
Originally Posted by brossa View Post
I will argue that you can't determine hemisphere by whether the shadow is to the north or south of the bottle; instead you can determine whether you are north or south of whichever latitude line has the noon sun directly overhead for that date. There may be a more elegant way of putting that. This line of latitude varies from the Tropic of Capricorn to the Tropic of Cancer depending on the date. So, on June 21st (summer solstice) if the shadow at noon is pointing south, the most that you can say is that your latitude is somewhere between ~23.5 deg North, and 66.5 deg South (any further South on that date and the Sun wouldn't ever rise). But on December 22nd, if the noon shadow was pointing South, you would say that you were between ~23.5 deg South and 66.5 deg S (again, any farther South and the Sun wouldn't have ever set).
Actually, they are correct. They are only discussing using the direction of the shadow on the special case of an equinox.
Quote:
Had you been kidnapped at equinox season, when daylight has the same duration the world over, finding your latitude would be more involved, requiring, for example, finding the ratio between a shadow’s length and the height of a water bottle at noon, and identifying the hemisphere by which side of the bottle the shadow extends from (north or south).
This also addresses your second point about determining latitude, which can be done can be found by the length of the bottle’s shadow at noon. No shadow means that there are six more weeks of winter that you are on the equator. The increasing length of the shadow as a ratio of the height of the bottle will tell you your latitude.
  #93  
Old 06-15-2019, 02:40 PM
brossa is online now
Guest
 
Join Date: Feb 2005
Posts: 1,141
Rereading that, I will grant that it can be read as applying only to equinox dates, which would be correct. I was reading the clause 'finding your latitude would be more involved...' as being true in general, which is not correct.

And their statement about a snowy night doesn't demonstrate that it isn't near an equinox, so the 'call at dawn and dusk only' can't be guaranteed to give your latitude anyway.
  #94  
Old 06-16-2019, 03:22 AM
kaylasdad99 is offline
Charter Member
 
Join Date: Sep 1999
Location: Anaheim, CA
Posts: 31,827
Why would the kidnappers tell their victim to wait until sunrise to place the call? They're terrorists/extortionists; they have no plausible motivation to give their victim a "sporting chance"...

Unless the satellite phone only works during daylight hours (which strikes me as kinda ridiculous, even though I have virtually ZERO knowledge of satellite phones and their workings).
  #95  
Old 06-16-2019, 04:28 AM
TokyoBayer's Avatar
TokyoBayer is online now
Guest
 
Join Date: Oct 2003
Location: Taiwan
Posts: 10,498
Quote:
Originally Posted by brossa View Post
And their statement about a snowy night doesn't demonstrate that it isn't near an equinox, so the 'call at dawn and dusk only' can't be guaranteed to give your latitude anyway.
I didn't read that the comment about the snowy night as proving it wasn't near an equinox. ISTM that it was just more extraneous information.

The person being kidnapped would know if it's near the equinox. They provided a method of solving for both the case of not near an equinox and hinted at the more complicated solution for the other.
  #96  
Old 06-16-2019, 10:13 AM
Hampshire is online now
Member
 
Join Date: Jan 2003
Location: Minneapolis
Posts: 11,037
Not sure if I figured right but I calculated each second on the clock as covering about 3.5 longitudinal miles? So depending on how accurately the observer got his sunrise time correct, how accurately the listener noted it, and the phone delay, the margin of error could be rather large. Being 5 seconds off the exact time gives you 17 miles to search.
  #97  
Old 06-16-2019, 11:08 AM
dtilque is online now
Charter Member
 
Join Date: Jan 2000
Location: My own private Nogero
Posts: 6,968
Quote:
Originally Posted by Hampshire View Post
Not sure if I figured right but I calculated each second on the clock as covering about 3.5 longitudinal miles? .
That sounds wrong. Consider the Earth's circumference is about 25000 mi and there are 86400 sec/day. A second should be around .3 miles. You may have slipped a decimal point in your calculations.

Last edited by dtilque; 06-16-2019 at 11:11 AM.
  #98  
Old 06-16-2019, 11:29 AM
pulykamell is online now
Charter Member
 
Join Date: May 2000
Location: SW Side, Chicago
Posts: 47,661
Quote:
Originally Posted by kaylasdad99 View Post
Why would the kidnappers tell their victim to wait until sunrise to place the call? They're terrorists/extortionists; they have no plausible motivation to give their victim a "sporting chance"...
Because this is a brain teaser and not a real-life situation? I mean, why do Bond villains have such complicated methods of attempting to kill 007 that allow him a way out? It's all fiction. Don't fight the hypothetical.
  #99  
Old 06-16-2019, 03:18 PM
Dag Otto is offline
Guest
 
Join Date: Sep 2003
Location: Las Cruces
Posts: 5,438
The title of the riddle asks "can you escape at dawn?" Calling once at sunrise and then later at sunset makes the answer to this as no, at least not by dawn on the first morning.
  #100  
Old 06-16-2019, 07:44 PM
Kedikat is offline
Guest
 
Join Date: Aug 2014
Posts: 488
You could tear a long strip of paper bag, if you do it somewhat spiral. Plant a water bottle before sunrise. Mark off the end of the shadow when it equals the length of your paper tape.
Mark the opposite point at sunset.
Using the paper tape and the water bottle as the center. Do some very basic geometry in the sand of intersecting arcs. This will give you a 90 degree line from the east West line. Noon at your location.
If you are not at the Equator. The North South offset of your arc intersections may also help in Latitude estimate. The North intersection being X percent longer than the South one or opposite.
Wait till local noon and tell them that when you make the call.

You suck at navigation. But for some reason you paid attention in geometry. As the sat phone makers also seemed to pick and choose abilities of their system.
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 11:03 PM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2019, vBulletin Solutions, Inc.

Send questions for Cecil Adams to: cecil@straightdope.com

Send comments about this website to: webmaster@straightdope.com

Terms of Use / Privacy Policy

Advertise on the Straight Dope!
(Your direct line to thousands of the smartest, hippest people on the planet, plus a few total dipsticks.)

Copyright © 2018 STM Reader, LLC.

 
Copyright © 2017