 |
This antique Reploglobe from the
1930s has a 24-hour clock in the
base. |
The equator (A), the Tropics of Cancer
and Capricorn (B), (C) , and the Arctic and Antarctic Circles
(D), (E) are the major
delineations.
Lines of longitude
(F) are called meridians. They are
marked in intervals of 10 or 15 degrees, beginning with the
zero-degree Greenwich Meridian. Every 15 degrees of longitude equals
one hour. In the United States, time zones fall roughly along four
meridians, each 15 degrees, or one hour, apart—75 degrees (Eastern),
90 degrees (Central), 105 degrees (Mountain) and 120 degrees
(Pacific).
The meridian or semi-meridian allows the
globe to spin on its geographic polar axis, an imaginary line
through the North and South Poles (G), (H). A mariner’s compass aligns with the magnetic poles, which are different from the geographic poles.
Globes generally are tilted at a 23.5-degree angle,
known as the angle of inclination. It represents the tilt of the
earth’s axis in relation to the sun, the reason why much of the
world experiences a change of seasons.
Time dials (I) are found at the North Pole of
many globes. They allow you to calculate the time in one part of the
world in relation to another using meridians, or longitude. The 24
demarcations correspond to the meridians and show the 24 hours in a
day. For instance, when it’s 1:00 p.m. on the 75th meridian west—New
York—it’s 6:00 p.m. at the zero meridian—London.
Latitude lines (K) are called parallels. They
are usually shown 10 or 15 degrees apart, starting from zero at the
equator.
The analemma (L), the figure 8 diagram found in the
Pacific, shows where the sun’s rays fall vertically upon the earth.
This occurs only between the Tropics of Cancer and Capricorn. The
longest and shortest days of the year occur when the sun’s rays are
most direct (the summer solstice) and most indirect (the winter
solstice).
The Tropic of Cancer and the Tropic of Capricorn
(B), (C) indicate the position of the
sun. The Tropic of Cancer depicts the sun’s most
northerly path, and the Tropic of Capricorn its most southerly
path.