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Colatitude
 
 
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In spherical coordinates, colatitude is the complementary angle of the latitude
Latitude

Latitude, usually denoted symbolically by the Greek letter phi gives the location of a place on Earth north or south of the equator. Lines of Latitude are the horizontal lines shown running east-to-west on maps ....
, i.e. the difference between 90° and the latitude.

colatitude is useful in astronomy
Astronomy

Astronomy is the science of Astronomical object and Phenomenon that originate outside the Earth's atmosphere . It is concerned with the evolution, physics, chemistry, meteorology, and motion of celestial objects, as well as the physical cosmology....
 because it refers to the zenith distance of the celestial pole
Celestial pole

The north and south celestial poles are the two imaginary points in the sky where the Earth axis of rotation, "infinitely extended", intersects the imaginary rotating sphere of stars called the celestial sphere....
s. For example, at latitude 42°N, Polaris
Polaris

Polaris is the brightest star in the constellation Ursa Minor. It is very close to the north celestial pole , making it the current northern pole star....
 (approximately on the North celestial pole) has a latitude of 42°, so the distance from the zenith
Zenith

In broad terms, the zenith is the direction pointing directly above a particular location . Since the concept of being above is itself somewhat vague, scientists define the zenith in more rigorous terms....
 (overhead point) to Polaris is 90 - 42 = 48°.

Adding the declination of a star to the observer's colatitude gives the maximum latitude of that star (its angle from the horizon
Horizon

The horizon is the apparent line that separates earth from sky.More precisely, it is the line that divides all of the directions one can possibly look into two categories: those which intersect the Earth's surface, and those which do not....
 at culmination
Culmination

In astronomy, the culmination, at a given point, of a planet, star, constellation, etc. is the time within the diurnal motion when it appears on an observer's meridian ....
 or upper transit).






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In spherical coordinates, colatitude is the complementary angle of the latitude
Latitude

Latitude, usually denoted symbolically by the Greek letter phi gives the location of a place on Earth north or south of the equator. Lines of Latitude are the horizontal lines shown running east-to-west on maps ....
, i.e. the difference between 90° and the latitude.

Astronomical use

The colatitude is useful in astronomy
Astronomy

Astronomy is the science of Astronomical object and Phenomenon that originate outside the Earth's atmosphere . It is concerned with the evolution, physics, chemistry, meteorology, and motion of celestial objects, as well as the physical cosmology....
 because it refers to the zenith distance of the celestial pole
Celestial pole

The north and south celestial poles are the two imaginary points in the sky where the Earth axis of rotation, "infinitely extended", intersects the imaginary rotating sphere of stars called the celestial sphere....
s. For example, at latitude 42°N, Polaris
Polaris

Polaris is the brightest star in the constellation Ursa Minor. It is very close to the north celestial pole , making it the current northern pole star....
 (approximately on the North celestial pole) has a latitude of 42°, so the distance from the zenith
Zenith

In broad terms, the zenith is the direction pointing directly above a particular location . Since the concept of being above is itself somewhat vague, scientists define the zenith in more rigorous terms....
 (overhead point) to Polaris is 90 - 42 = 48°.

Adding the declination of a star to the observer's colatitude gives the maximum latitude of that star (its angle from the horizon
Horizon

The horizon is the apparent line that separates earth from sky.More precisely, it is the line that divides all of the directions one can possibly look into two categories: those which intersect the Earth's surface, and those which do not....
 at culmination
Culmination

In astronomy, the culmination, at a given point, of a planet, star, constellation, etc. is the time within the diurnal motion when it appears on an observer's meridian ....
 or upper transit). For example, if Alpha Centauri
Alpha Centauri

Alpha Centauri ; is the brightest star in the southern constellation of Centaurus and an established binary star system, Alpha Centauri AB ....
 is seen with a latitude of 72° north (108° south) and its declination is known (60°S), then it can be determined that the observer's colatitude is 108 - 60 = 48 (i.e. their latitude is 90 - 48 = 42°S).

Stars whose declinations exceed the observer's colatitude are called circumpolar
Circumpolar

The term circumpolar may refer to:* circumpolar navigation: to travel the world "vertically" traversing both of the poles* the Antarctic Circumpolar Current...
 because they will never set as seen from that latitude. If an object's declination is further south on the celestial sphere than the value of the colatitude, then it will never be seen from that location. For example, Alpha Centauri will always be visible at night from Perth, Western Australia
Perth, Western Australia

Perth is the List of Australian capital cities and largest city of the Australian States and territories of Australia of Western Australia. With a population of 1,554,769 , Perth ranks fourth amongst the nation's cities, with a growth rate consistently above the national average....
 because the colatitude is 90 - 32 = 58, and 60 is greater than 58; on the other hand, the star will never rise in Juneau because its declination of -60° is less than -32° (the negation of Juneau's colatitude).