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Latitudes in the Northern Hemisphere are given in positive degrees, and latitudes in the Southern Hemisphere are given in negative degrees. Chicago is approximately located at latitude 42 degrees north.
Latitude circles reside in planes that are perpendicular to the Earth's axis of rotation. The largest latitude circle is latitude zero degrees, or the Equator. The smallest latitude circles, of radius zero, are the North and South Poles. We travel on the Earth on our latitude circles.
Latitude lines are circles that go around the Earth such that each point on the circle makes the same angle between itself, the center of the Earth, and the point on the Equator directly south of it.
Latitude and Longitude are imaginary crisscrossing lines that demarcate the Earth.
The International Date Line can be confusing. Why is it one day on one side of the line, and another day on the other side? One way to understand this is to consider Magellan's circumnavigation of the Earth (1519 to 1522). Magellan left Portugal, but he didn't make it home. When the remnants of his crew returned to Portugal, they asked what day it was, and were astounded to find out that one more day had passed for the people of Portugal then for Magellan's crew. In essence, Magellan's crew had chased the Sun westward, and so had seen one less sunrise and sunset.
Also notice that longitude angles only go up to 180 degrees. Longitudes 180 degrees east and 180 degrees west are both called the International Date Line, which is the imaginary line separating the new calendar day from the previous calendar day. The new calendar day is what is happening east of the Prime Meridian when the local time in England is midnight. The previous day is what is happening west of the Prime Meridian when the local time in England is midnight.
Longitude lines are half great circle arcs, or meridians, going from the Earth's North Pole to its South Pole. Longitude lines are separated by degrees. By convention, zero degrees longitude goes through Greenwich, England, with the other longitude lines being described as so many degrees east or west of zero degrees. Because zero degrees longitude goes through Greenwich, we call this meridian the Prime Meridian. Notice that 15 degrees of longitude corresponds to one 24th of the Earth's rotation, so local time should change by about an hour as you travel 15 degrees longitude east or west.
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