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You've probably heard stories of people navigating by the sun, moon, and stars. The sun and moon can be used to easily find the direction someone was traveling, and the stars could be used to determine latitude (how far north or south of the equator a location is). Longitude is a different story for early explorers, because of one simple thing: time. Longitude is calculated by observing the difference in local time between two points. In order to determine the time difference, navigators first needed an accurate way of keeping time. Every hour, the earth rotates through 15 degrees longitude.Although mechanical clocks have been around since the 9th century, they were either too bulky or delicate for sea travel. It wasn't until the 18th century that John Harrison invented the first clock suitable for determining longitude at sea. As marine clocks became more common, it became easier and easier for navigators to find their true place in the world.
The types of images you're talking about are known as false-color images. This is because the colors you see in the photograph are not exactly the colors you would see with your eyes. The human eye can only see what's called the "visible portion" of the electromagnetic spectrum. Certain types of film, though, can "see" other parts of the electromagnetic spectrum invisible to the human eye. When these photographs are printed (or displayed on a monitor), they contain three channels of color that combine to form the image. In false-color images, one or more of those channels is replaced by the color information that is normally invisible to the eye, and the image looks funny. These images are extremely useful in some situations. For example, false color images are often used by farmers to see how healthy crops are in the field (healthy crops usually show up as a bright red)
The short answer is this: resolution. The pictures that Google Earth uses are just like the kind you can take with a regular digital camera. That means they are made up of a grid of tiny picture elements (known as pixels) that hold a single. The more pixels per inch you have in an image, the higher the resolution and the more detail you can show. As you zoom into an image, the computer simply scales up the size of the pixels. This is what causes blocky images. Google Earth tries to smooth out some of the blocky pixels by blending the colors of nearby pixels together, hence, the blurry images. Google Earth is trying to minimize this by adding higher-resolution images at a variety of zoom levels all over the world.
Geocaching is a fun activity where people try to locate items hidden all over the world. Participants use GPS devices or written clues to track down a container called a cache. Inside, it may have some small treasures to keep, or a pen and logbook to keep track of who found the cache and when. Geocaching began gaining popularity in May 2000 with the removal of "Selective Availability," a feature that intentionally introduced accuracy errors in non-military GPS units. After its removal, geocachers were able to get within 6-20 feet of the physical location of the cache. When the cache is found, participants sign the logbook inside. If there are treasures inside (small figurines, stickers, etc), there is a courtesy rule of "take one, leave one." If you decide to take one of the treasures, it is polite to replace it with another. Then the cache is placed back where it was for another group of cachers to find.