Ann Bartlett, age 14, of Costa Mesa, California, for her question:
How many miles long are the degrees of latitude and longitude?
You can use the fascinating lines of latitude and longitude to invent 1,000 brain teasing games. As you know, they are sectioned in degrees with 360 degrees to the circle. Challenging queries begin when you realize that the length of a degree ranges from nothing to more than 69 miles.
A city map is charted with a network of intersecting streets that can be measured in flat miles. But a chart to pinpoint all locations in the world poses another problem. The world is a round globe. Any straight guideline on its surface that completes its duty goes all the way around and returns to home base. It is a circle. And circles are more tricky to section that straight lines. What's more, each spot on the globe needs to be charted by a north and south guideline and by another that runs east and west. The east west markers are the lines of latitude. The north south markers are the lines of longitude.
The lines of latitude are easier to understand. The degrees of distance between them vary, but not very much. Those near the equator are somewhat shorter and those nearer the poles somewhat longer, but the average distance between the parallel lines that circle around the globe from east to west is roughly 69 miles. We must allow for this slight variation on the basis of the fact that nothing is 100 per cent perfect. The earth is not a perfect sphere.
The lines of longitude run north and south from pole to pole. They section the globe like an orange and the wedges are thickest around the wide waist of the world's equator. From the equator, they taper together to meet at the north and south poles. The distance between them at the equator is a little longer than 69 miles, very close to the average distance between the degrees of latitude. But as they taper together, the degrees that separate them get shorter. Along latitude 30, the degrees of longi¬tude are about 60 miles and along latitude 60 they are less than 35 miles. At each pole, they merge on one spot and the longitude degrees are zero.
The distance around every circle, large or small, is sectioned in 360 equal degrees. The biggest circles naturally have the longest degrees. Latitude 0 at the equator is intersected by 360 degrees of longitude, 180 degrees for the east and west hemispheres of the globe. The latitude circles get smaller toward the poles, but they divide the global lines of longitude into fairly even degrees of latitude. On the other hand, the lines of longitude which intersect the smaller circles of the higher latitudes grow closer together, and the degrees between the longitudes grow shorter.
The degree of a circle is divided into 60 minute segments and each minute is divided into 60 second units. Minutes and seconds remind us of clocks and degrees of longitude are indeed related to time. But they do not equal the hour sections of a clock. They mark off the 24 hour path of the sun around the globe. Each hour equals 15 longitude degrees. One minute of clock time equals 15 minutes of longitude and one clock second equals 15 seconds of longitude distance.