Coordinates For Planetary Exploration
When you're exploring another world you need to record where you find interesting things. This is vital if you want to be able to find them again or share you discoveries with other explorers. Fortunately, scientists have already established a nice system of coordinates for spheres that is used on Earth and other planets.
But first, since I'm so fond of coordinate systems, I'd to discuss somes we use every day. All over the world we give buildings addresses. The system requires that streets be given names while buildings are given numbers. This works pretty well, but since the names are mostly randomly assigned if you're in a new area it can be very hard to find a particular street. Since building numbers are not random but assigned in order, once you've found the street it is always easy to find the building. On much of the island of Manhattan most street names are not randomly assigned. Instead the streets are laid out in a grid with numbered avenues running one way and numbered streets running the other. If you're in New York trying to find the building at 5th Avenue and West 34 Street you shouldn't get lost.
This isn't the only system we use to keep of locations. We use zip codes even though they only make sense to the Post Office. We use phone numbers but program our cell phones so we don't have to actually remember the number. In school, we learned the Carteasian Coordiante System that used an X and Y axis.
The universally used coordinate system for planets is the "Geodetic Coordinate System". It uses latitude and longitude to specify locations on the surface of a planet. Latitude is a measure of how many degrees something is from the equator. The north pole is at 90 degrees north latitude and the south pole is at 90 degrees south latitude. Latitude divides a globe into a northern hemisphere (the area to the north of the equator) and a southern hemisphere.
Longitude is a measure of how far east or west a point is from an origin. Like latitude, it is measured in degrees. Where latitude could use the equator as a natural origin, there is no natural origin for longitude. So, some convenient or random line is selected to serve as the "prime meridian", the line of 0 longitude. Usually, longitude is said to increase as one moves to the east. On Earth, the agreed upon prime meridian runs through the astronomical observatory in Greenwich England. All measurements of east and west are referenced to this line. Sometimes longitude is measured from 0 degrees all the way around the planet to 360 degrees. Other times, you'll see it measured from 0 to +180 degrees and from 0 to -180 degrees. On rare occasion, you might even find a resource that has longitude increasing to the west.
The PEP map displays the geodetic coordinates of mouse at the bottom of the frame. Any time you need to know the latitude and longitude of something, just move the mouse over it. The PEP 3D display also displays the geodetic coordinates of your virtual spaceship. Note that this isn't the location of what you might be looking at out in front of you. It is where you are looking from.