1. 18 September 2013

2. How does my phone figure out my location? Why GPS of course! Which is to say the array of ~30 US Satellites is used.

3. How does GPS work?  GPS satellites broadcast their position with an accurate timestamp  GPS receivers use the position and timestamp of at least 4 visible satellites to calculate how far away the satellites are  Receivers then make spheres based around each satellite and use their intersection for the receiver location

4. A schematic of circles showing the location of the gps receiver, which is the red dot.

5. Accurate Time GPS satellites have 4 cesium or rubidium atomic clocks on board. An SI second is defined by the duration of 9,192,631,770 cycles of radiation corresponding to the transition between two energy levels of the cesium-133 atom. A cesium clock operates by exposing cesium atoms to microwaves until they vibrate at one of their resonant frequencies and then counting the corresponding cycles as a measure of time.