MadSci Network: Earth Sciences

Re: Is the 12 pm sun always center around the world?

Date: Sun Jun 4 12:57:18 2006
Posted By: Gene Marlin, Graduate, Geology
Area of science: Earth Sciences
ID: 1149360554.Es

 Hi Marino,

 Your intuition is right on.  

 The Sun will always be at its highest above the horizon for that day and 
that latitude at local noon anywhere in the world, except where 
timekeeping conventions arbitrarily cause noon to occur at some other 

 This is not to say that the Sun will be directly overhead, which for 
most of the world never actually happens because the Earth is tilted on 
its axis. The altitude of the Sun over the southern horizon, at noon, is 
caused by the position of the Earth in its orbit around the Sun, and is 
the cause of the seasons. 

 The lines of latitude farthest from the equator at which the Sun can 
appear directly overhead are the Tropic of Cancer (about 23 degrees N) 
and the Tropic of Capricorn (about 23 degrees S). This occurs at noon on 
the solstices, Northern Hemisphere Summer and Southern Hemisphere Summer 
solstices, respectively. North or south of these parallels the sun can 
never appear directly overhead. The Sun can appear directly overhead at 
the geographic equator at noon on two days a year, the vernal and 
autumnal equinoxes. 

 According to tradition, Eratosthenes used this observation to make a 
fairly accurate estimate of the diameter of the Earth (1). Also, 
navigators have used this principle for centuries to estimate their 
latitude at sea using a sextant, the date of the year, and astronomical 
tables. Calculating their longitude was much harder because they had to 
develop accurate timekeeping at sea, but was done by measuring the time 
local noon occured and comparing to the time of local noon at the prime 

Hope this helps. 

--Gene Marlin

(1) MadSci Archive

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