Geocaching class research

Some of the links that I am looking at as part of research for the Middle School

Before the GPS:

How does GPS work:

How does GPS work:

Triangulating from Satellites:

Hows does GPS work:

The fourth satellite:

The distance of the satellites:

The location of the satellites:

How does GPS work:

Alternative satellite systems:

Heavens Above - What is above us:

NASA - J-Track 3D:

How does GPS "triangulation" work:

GPS - Wiki

The almanac consists of coarse orbit and status information for each satellite in
the constellation, an ionospheric model, and information to relate GPS derived time
to Coordinated Universal Time (UTC). Words 3 through 10 of subframes 4 and 5 contain
a new part of the almanac. Each frame contains 1/25th of the almanac, so 12.5 minutes
are required to receive the entire almanac from a single satellite.

GPS satellite info: