Latitude

 

Latitude. There are three kinds of Terrestrial latitude: astronomical, geographic and geocentric. (1) Astronomical: the angle between the direction of the plumb-line and the plane of the Earth's equator. If the Earth were a homogeneous sphere without rotation, the plumb-line would point toward its center -- but the Earth is not an exact sphere. Deviation due to inequalities of the Earth's surface is termed Station Error. (2) Geographic: the latitude used in drawing terrestrial maps. It is astronomical latitude corrected for station error. (3) Geocentric: from a given point on the Earth's surface subtend a line to the Earth's center, and there compute the angle between this line and the plane of the equator.

 

It is important to distinguish between Geographical Latitude measured N. or S. of the Equator, and Celestial Latitude measured N. or S. of the Ecliptic. Geographical Latitude is thus comparable to Declination rather than Celestial Latitude.

 

There are also Galactic Latitude, angular distance on the celestial sphere measured from the medium plane of the Milky Way; and Heliographic Latitude, angular distance on the Sun's sphere, N. or S. of its Equator.

 

There are also three varieties of its Celestial equivalent: (a) that which parallels the Horizon, which is called altitude; (b) that which parallels the Equator, which is called declination; and (c) that which parallels the Ecliptic, which is called Latitude. (v. Celestial Sphere.) Since the apparent motion of the Sun, resulting from the Earth's motion in orbit, is itself the Ecliptic, the Sun can have no Latitude. Since the orbits of the planets are inclined to the Ecliptic at an angle of more or less obliquity, each planet, without Latitude when it intersects the Ecliptic, increases in latitude as it approaches the square to its Nodes: for one half its orbit in North Latitude, the other half in South Latitude. The maximum possible Latitude of each planet, and the location of its Node, are as follows:

 

...Planet.......Node as of 1946.....Maximum Latitude

...Moon...................................5°17'

...Mercury.........47°32'.................7°

...Venus...........76°05'.................0°24'

...Mars............49°02'.................1°51'

...Jupiter.........99°46'.................1°18'

...Saturn.........113°04'.................2°29'

...Uranus..........73°39'.................0°46'

...Neptune........131°02'.................1°47'

...Pluto..........109°25'................17°09'

 

To Change Geographical to Geocentric Latitude, or the Reverse. These are equal at the equator and the poles. At 45° the Geocentric Latitude is the greater by about 4½ minutes. The following table shows the corrections for each degree of separation from either the horizon or the pole, whichever is the nearer, the correction to be added to Geographic or subtracted from Geocentric Latitude, to change one to the other.

 

.. 1º ....... 24".2

.. 2º ....... 24".36

.. 3º ......1'12".47

.. 4º ......1'24".16