[Abdelrahman Hussein (OP)]

If you were in the desert at 12 Am. You know that there is a town 12 hours east and have water for only 6 hours; However, you can bear another 6 without water. You don't know the directions but have to survive. What shall you do?

[Bored chemist]

Can you clear something up?
12 am is ambiguous.
Do you mean noon, or midnight?

[Abdelrahman Hussein (OP)]

Can you clear something up?
12 am is ambiguous.
Do you mean noon, or midnight?

midnight

[Bored chemist]

Is it cloudy, or can I see the stars?

[Abdelrahman Hussein (OP)]

Is it cloudy, or can I see the stars?

you can see the stars 

[Bored chemist]

Then I can use something like this to find out where I am.
https://in-the-sky.org/skymap.php

[jeffreyH]

You say you don't have directions but if you can find north do you have enough information to work it out from there?

[alancalverd]

Not a problem in the northern hemisphere: you can see Polaris, so your destination is on your right.

You need a bit more subtlety south of the equator but you know the stars rise in the east, so you can make a start as soon as you have confirmed the motion of a constellation (at 15 degrees/hour that won't take long) and refine your track as you identify those constellations that are covering the least apparent distance - the center of their arc is south.

In either case the sun will rise at some point on your journey. If you know the local time and season, you can estimate an east correction from its first appearance, then use a stick and watch as a sun compass as you march.

I was disappointed by a recent TV program in which a group of engineers and survival experts spent several days sweating in the desert and arguing about how to convert a wrecked plane into a car, to drive 10 km to a main road. Knowing were the road was, they could have walked out on the first night.

[Bored chemist]

It's perhaps appropriate - at this festive  time of year.
Watch the horizon until a new star rises in the East, then walk towards it.

My version was a bit more sophisticated and has the disadvantage of needing a computer, but it lets you start slightly earlier, because you don't need a star to appear.With the way the puzzle is framed, you have zero time to spare.

I was disappointed by a recent TV program in which a group of engineers and survival experts spent several days sweating in the desert and arguing about how to convert a wrecked plane into a car, to drive 10 km to a main road. Knowing were the road was, they could have walked out on the first night.

They probably had to film it half a dozen times until they found a group dumb enough to do that. (or maybe they just paid them to act dumb)

In either case the sun will rise at some point on your journey. If you know the local time and season, you can estimate an east correction from its first appearance, then use a stick and watch as a sun compass as you march.

You have no time for errors or corrections.

[alancalverd]

The shortest track is a great circle, so if you are not on the equator, you will need to make en-route course corrections anyway!

As for the TV show, it was clearly intended to demonstrate what any group of survivors could achieve. If you pick six people at random, they are almost certain to include a special forces officer, a professional explorer, an aerobatic champion, a blacksmith, a civil engineer, and a hysteric who can be coaxed into remembering the automotive engineering degree syllabus just before the water runs out. And a camera crew, of course.

[jeffreyH]

When you have the security of rescue if it all goes wrong you are less likely to panic. Clear headed action is easy to advise from the comfort of an armchair. In the OP the exit is known to be east so it has to be assumed that was the intended destination. If so it has to be an incompetent bunch that didn't plan properly in advance for a desert journey.

[alancalverd]

But panicking was exactly what they did in the TV show!

[evan_au]

You need a bit more subtlety south of the equator

Those of us who live in the Southern hemisphere, far enough south to see the Alpha Centauri and the Southern Cross constellation, are taught to use the method described here:
https://maas.museum/observations/2013/01/23/finding-south-using-the-southern-cross/

use a stick and watch as a sun compass as you march.

That used to work when people had watches with moving hands. You have to use more imagination when everyone has digital watches. Maybe your smartphone has a retro "analog" display mode?

The other trick is that watches with moving hands were developed in the Northern hemisphere to mimic the motion of a sundial shadow.

The sundial shadow goes in the opposite direction in the Southern hemisphere, so you have to do a mental mirror-image of the hour-hand position (ideally taking into account any daylight savings, of course).

[Bored chemist]

The sundial shadow goes in the opposite direction in the Southern hemisphere, so you have to do a mental mirror-image of the hour-hand position (ideally taking into account any daylight savings, of course).

That may well be easier with a smart phone

[alancalverd]

Quote

    use a stick and watch as a sun compass as you march.

That used to work when people had watches with moving hands. You have to use more imagination when everyone has digital watches. Maybe your smartphone has a retro "analog" display mode?

I think you will find that the sun moves at 15°/hr whether your watch has hands, feet or numbers.

[glot]

Go to the pub. 12 hours is nothing to go with out water at night. If however, it is in the heat of the day, go 24 hours with out drinking what little fluid you have. This causes your kidneys to shut down. Then drink your water in decent amounts, not just little sips. This way more gets in to your blood. If a body has been trained, it is possible to survive on a cupful of water in a hot desert per day.

[Bored chemist]

it is possible to survive on a cupful of water in a hot desert per day.

How?
You need more than that to keep the temperature within acceptable limits by latent heat of vaporisation.