1
$\begingroup$

If I was in a coma and woke up at night in the desert, what knowledge would I know instantly and after 30 days of observation?

  • Can I figure out the general directions, i.e. where North, South, East, and West is?
  • Can I conclude my exact or approximate location on the world map?
  • Can I know the current season?

And during day time: If I draw the arc path of the sun from rise to sunset for a longer period of time - what info can I infer from it?

$\endgroup$
5
  • $\begingroup$ You would first notice that there are a lot of stars at night. $\endgroup$
    – Rob Adams
    Jun 29 at 6:37
  • $\begingroup$ Welcome to astronomy SE! I edit your question a bit to make it easier to read and understand - I hope I kept your intension. $\endgroup$
    – B--rian
    Jun 29 at 12:33
  • 3
    $\begingroup$ @B--rian some edits changes my question entirely $\endgroup$
    – huab
    Jun 29 at 12:57
  • $\begingroup$ so I make some edits, but thank you for the rearrangement and for make it more readable $\endgroup$
    – huab
    Jun 29 at 13:03
  • $\begingroup$ Sherlock says to Watson, "Wake up and look at those stars. What do they tell you?" "They tell me," says Watson, "that we are insignificant specks in a nearly infinite Universe. What do they tell you?" "That someone has stolen our tent!" $\endgroup$
    – JohnHunt
    Jul 1 at 2:20
4
$\begingroup$

OK! So it's night time in the desert.

If it is hot or very warm it's summer, even at night.

If it is cold it's most likely winter.

If it is a pleasant temperature or mild, it's anyone's guess.

If you are having difficulty breathing and it is cold, you are on a very high mountain - Andes, Himalayas.

If it is overcast and you don't recognize any on the landmarks, you don't know where you are.

If it is not overcast and you can see most of the sky that's good.

Do you have a very basic knowledge of stars in the night sky where you normally live. If yes good, if not, the stars aren't going to help you.

Look at the sky directly above you. Choose a bright star close to the top of the sky above you. Wait a while. If you have a watch, wait for one hour. Note the direction the star has moved to, the direction it moved to was west.

Do you recognize the pole star. Do you know about the pole star? Is it relevant to your hemisphere? If yes, you normally live in the northern hemisphere. If not you normally live in the southern hemisphere, where the Southern Cross will be of importance.

Having located west by the overhead star, put your left side towards west. Look ahead. You are now facing north. Look for the pole star. If it is high in the sky you are in the northern latitudes. If it is lower in the sky you are likely in the southern latitudes of the northern hemisphere.

If you don't see the pole star you may be in the southern hemisphere. Put west to your right side, as per the overhead star you watched before. You are now facing south.

Do you see the Southern Cross (Crux) and the associated Two Pointers (Alpha Centauri and Beta Centauri). If they are very close to the horizon you might be very close to the equator.

To confirm these initial observations. Do you recognize any major constellations such as Orion or Scorpio? Do you really know what the Moon looks like - the features on the face of the Moon? Do you know what they look like from were you normally live?

Can you see either in the sky now. Do they look the same? If yes you are in the same hemisphere you normally live in. If they look strange - upside down. You are in the hemisphere opposite to where you normally live.

You've just spent the rest of the night looking at the sky and the Sun is up. Observe the path Sun, in the sky, during the course of the day. If it is low, it winter. If it is high, it's summer. The daytime temperature will also confirm this.

$\endgroup$
4
  • $\begingroup$ I didn't choose a right word; I meant weather forecasting (by stars and planets places and movements); and I meant by season the dates (if it is 21/3 , 21/6, 21/9, 21/12 or between them), and ofcourse Thank you $\endgroup$
    – huab
    Jun 29 at 13:37
  • 1
    $\begingroup$ @huab If you can make accurate observations of the stars & the Sun it's not too hard to get a good idea of your latitude, and the date. But it's very difficult to determine your longitude. Newton figured out a method based on the Moon, but to use his method you need an ephemeris of the Moon, and very accurate observations. $\endgroup$
    – PM 2Ring
    Jun 30 at 6:15
  • $\begingroup$ @PM 2Ring Are there satellites moves with longitude paths or in paths from which we can infer our longitude from it? $\endgroup$
    – huab
    Jun 30 at 16:15
  • 1
    $\begingroup$ @huab: If you had a watch which had the time for where you normally live & you knew time difference between where you normally live and UTC (GMT) you can find longitude for the desert location by noting the time on the watch at noon in the desert & doing the mathematics to find where the desert location is in relation to UTC & the prime meridian. $\endgroup$
    – Fred
    Jun 30 at 16:25
1
$\begingroup$

The wind directions are not difficult to find. Just look at the dearest star to anyone of us, the Sun. It sets in the west and rises in the east. You could also look at the direction in which the stars move. This is the east-west (longitudinal) direction.

When you notice the star that stays fixed in the sky you will know that it is Polaris. Just for double check the north. This can only be done though when you are in northern regions.

So that's settled. What about your latitude? Knowing the time of year you should be able to know this by looking at the constellations. If you see the big dipper at an angle wrt to the azimut line you can calculate you latitude. This angle varies with the seasons but because you know the season this will be no problem. You could also look at the angle Polaris makes wrt to the line going straight up from you. When you are in southern regions the night sky is different and you have to make use òf different constellations.

What about your longitudinal direction? This is more difficult. Every longitude shows the same nightsky. So here you have to take other measures. You have 30 days to find out. What could you do? You could look at the weather. Every region has its own pattern. In this way you know both longitudinal and latitudinal directions. But 30 days is too little to know, even if you know what season it is.

So there will remain uncertainty about your longitude, while you can be pretty sure where you are wrt north-south direction.

But how do you know the time of year? Look at Polaris or a star in the south. Its latitude should tell you. The direction in which it changes position should tell you the month.

$\endgroup$
11
  • 3
    $\begingroup$ Determining the latitude is much simpler than determining the longitude. The latitude can be determined by the altitude of Polaris (or sigma Octans if in the southern hemisphere). I cannot think of any method to determine the longitude without having some external reference (such as the time at a known time zone). If you have a watch from your home, and if the Sun rises at midnight, you know that you are at a vastly different longitude. $\endgroup$
    – JohnHoltz
    Jun 29 at 18:10
  • $\begingroup$ @JohnHoltz You confuse latitude with longitude. $\endgroup$ Jun 29 at 18:11
  • 2
    $\begingroup$ In my language, latitude is the angle north or south of the equator. Standing at the north pole puts you at 90 N latitude (and no specific longitude since the lines of longitude converge at the pole). Since Polaris is straight overhead (within 1 degree), you can deduce that you are at 90 N latitude. If at 30 N latitude, the altitude of Polaris is 30 degrees above the horizon. $\endgroup$
    – JohnHoltz
    Jun 29 at 18:17
  • 1
    $\begingroup$ @Deschele Do you have a reference for that? I seriously doubt that latitude & longitude are reversed in Dutch! Both words are of Latin origin, and Latin was the standard language used for European scholarly writing for many centuries. Those two terms date from the 14th century. $\endgroup$
    – PM 2Ring
    Jun 30 at 5:40
  • 1
    $\begingroup$ Your last paragraph is wrong. The altitude of the celestial pole is equal to your latitude. You can determine the date from the Sun's declination (which varies in an approximate sine wave pattern), which can be determined from the Sun's altitude at high noon. So you just need to construct a sufficiently accurate sundial. Of course, if you're alone in the desert, you're probably too busy looking for food & shelter to build a sundial. ;) $\endgroup$
    – PM 2Ring
    Jun 30 at 8:13

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.