How to Ascertain Your Latitude and 



Longitude 



By Hereward Carrington 



THERE is a very simple way by 

 means of which the novice, un- 

 trained in astronomical observation, can 

 determine his latitude, without the aid of 

 complicated and expensive apparatus. 



If you were situated on the equator, 

 the north star would be directly north of 

 you. This star must be learned and iden- 

 tified, so that it can be picked out any- 

 where, at a moment's notice. This is all 

 the astronomy you need know — as the 

 location of this star will give the latitude. 



When half-way to the north pole the 

 north star is midway between the zenith 

 and the northern horizon. At the pole 

 it is directly overhead. In all other places 

 its "angle" varies, being for example, 30° 

 at New Orleans, 40° in Philadelphia, and 

 so on. The altitude of the north star is 

 the latitude of a place north of the equa- 

 tor. All that is necessary then, to deter- 



mine the latitude, is to measure the angle 

 of the north star and thus determine the 

 altitude of the celestial pole. This will 

 give the latitude. 



Take a pair of ordinary compasses. 

 Open them, and place one point in a level 

 window sill, holding the arm upright. 

 Now point the other arm of the compass 

 at the north polar star. The angle thus 

 formed by the pair of compasses will be 

 fairly accurate, provided the pointing has 

 been done carefully and the other arm is 

 held at right angles to the sill. 



When the compasses have been ad- 

 justed, as explained, proceed to measure 

 the angle formed by the arms of the 

 compass. This will indicate your lati- 

 tude. For every degree of curvature of 

 the earth, the north star rises one degree 

 from the horizon. It is thus an easy mat- 

 ter to see your latitude, from the number 

 of degrees made by the angle of your 

 compass. 



Another way to discover the latitude 

 of any given place — and a method much 

 more often used — is by means of the sun. 

 Observations of the sun are depended 

 upon by vessels at sea. 



The first thing to do is to ascertain 

 what is known as your true north-south 

 line. To do this you must know your 

 longitude and have the correct time. 

 Next, measure the altitude of the sun at 

 apparent noon — that is, when its shadow 

 is north. Place a curved piece of card- 

 hoard in the window, as shown in the 

 diagram, with the blind drawn down to 

 the wood of the upper window. The 

 angle made by the shadow will then in- 

 dicate the altitude of the sun with suffi- 

 cient accuracy. 



Next, consult what is known as the 

 "Analemma" (see diagram). If you live 

 in the northern hemisphere, you must 

 subtract from the declination of the sun 

 (which the analemma gives you) the 

 sun's declination. Subtract this result 

 from 90°, and the remainder is your lati- 

 tude. 



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