Planet Trek:

Mapping New Worlds


Part III: Concept Application: Mapping

Activity # 5 - Mapping Planetary Features

Lines of latitude and longitude are used as a coordinate system to locate places on a world's surface. By knowing the latitude and longitude for a specific feature, you can find its location anywhere on the planet (or moon). No two locations have the same coordinates.

Before continuing, you need to be familiar with the following terms:

  • Poles: The points at which the axis of the world's rotation extend through the surface - this is determined by the way the world spins
  • Equator: A line drawn equal distance between a world's north and south pole and runs east and west
  • Latitude: Lines drawn parallel to the equator, also called "parallels"
  • Longitude: Lines that intersect the equator at a right angle, run through both poles and run north and south
  • Prime Meridian: The line of longitude given the designation of zero degrees- determined arbitrarily

The poles are determined from the rotational axis of the world. Normally the equator is determined by finding the point on the axis midway between the poles and extending it outward through the surface. Other lines of latitude are determined the same way - by projection from the rotational axis that runs through the center of the world. Lines of longitude are determined by projection of the axis vertically, however the Prime Meridian is arbitrarily determined when mapping a new world.

Lines of latitude and longitude are drawn using a 360 degree circle. Latitude at is reported as 0 to 90 degrees followed by N. or S. Longitude is shown as 0 to 360 degrees followed by E. or W. on all worlds except the Earth and Moon. There, longitude is reported as 0 to 180 E. and 0 to 180 W.

The problem with mapping spherical worlds is creating a two dimensional drawing of a three dimensional world. Take a look at these images of the Moon and describe what happens:

Full Moon

Moon Map Projection

This flat projection is called a Mercator projections. There are many different kinds of projections that can be used when constructing maps, however the Mercator projection is the most popular. While it distorts area, it preserves direction. So, while they can be drawn to help us locate specific places on a terrestrial surface, they do have their limitations. Take a look at what happens when the surface of Mars is projected onto a flat surface for mapping:

Mars

Mars Map Projection

This system of using a coordinate grid can even be more of a challenge when mapping irregular shaped worlds, like asteroids. Look at the images of Eros:

Eros

Eros Map Projection

Regardless of shape, all terrestrial worlds have a latitude - longitude coordinate system established. This system helps observers, and maybe someday explorers, locate specific surface features. Using a latitude and longitude grid, you can map the surface of any world!


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