# How to determine the latitude

Imagine that you were shipwrecked and found yourself on an uninhabited island. In short, you have become Robinson. If so, then even the most mediocre Robinson should have the knowledge and skills that are completely optional for people of other professions. First of all, he should know **how to determine the geographical the latitude** of the area, that is, to find the geographical location of his involuntary abode.

This, unfortunately, is too briefly stated in most stories of old and new Robinsons. This annoying brevity may lead to despair, but it is not worth it that it abandons the enviable career of the only inhabitant of the deserted island. Therefore, let's look at the simplest ways to determine the geographical latitude. This skill may be of practical importance not only for inhabitants of unknown islands. There are still a lot of populated places that are not marked on the maps (and is it always a detailed map?) Therefore, the task of determining the geographical latitude may be confronted by many.

This is basically a relatively simple matter. Observing on a clear starry night behind the sky, you will notice that the stars slowly describe inclined circles on the firmament, as if the entire dome of the sky smoothly rotates on an obliquely fixed invisible axis. In fact, of course, you yourself, rotating with the Earth, describe the circles around its axis in the opposite direction. The only point of the stellar dome in the northern hemisphere, which retains immobility, is the one where the mental continuation of the earth's axis rests. This north "pole of the world" is not far from the bright star at the end of the tail of the Little Bear - the Polar Star. Having found it on our northern sky, we will find the position of the north pole of the world. But finding it is not difficult if you first find the position of the well-known constellation Ursa Major.

This is one of those points on the celestial sphere, which we will need to determine the geographical latitude. The second is the so-called "zenith" - a point that falls in the sky vertically over your head. In other words: zenith is a point in the sky where the mental continuation of the radius of the Earth rests on the space occupied by you. The degree of the sky arc between your zenith and the Polar Star is at the same time the degree distance of your place from the earth's pole. If your zenith is 30^{0} from Polaris, then you are 30^{0} degrees away from the earth's pole, which means 60^{0} from the equator; are on the 60th parallel.

Consequently, in order to determine the geographical latitude of any place, it is only necessary to measure the "zenith distance" of the Polar Star in degrees (and its fractions): then all that remains is to subtract this value from 90^{0} - and the geographical latitude is determined. as the arc between the zenith and the horizon contains 90^{0}, then, subtracting the polarizing distance of the polar star from 90^{0}, we get in the remainder nothing more than the length of the celestial arc from the pole star to the horizon, in other words, we get the height of the polar star burn ontom. Therefore, the geographical latitude of any place is equal to the angular height of the Polar Star above the horizon of this place.

If you want to be precise, you must take into account that the Polar Star does not strictly coincide with the pole of the world, but is 1 1/4^{0} from it. Therefore, the Polar Star does not remain completely motionless: it describes a small circle near the immovable celestial pole, either above or below it, then to the right, then to the left - by 1 1/4^{0}. Having determined the height of the Polar Star in its highest and lowest position (the astronomer would say: at the moments of its upper and lower "culminations"), you take the average of both dimensions. This is the true geographic latitude of the place.

But how to determine the geographical latitude, if you find yourself in the southern hemisphere? Likewise, stand only the difference that here it is necessary to determine the height not of the north, but of the south pole of the world. Near this pole, unfortunately, there is no bright star in the Polar genus. The famous Southern Cross shines quite far from the south pole; and if we want to use the stars of this constellation to determine the geographical latitude of the place, then we will have to take the average of two dimensions - with the highest and lowest position of the star.