This week I was in Rotterdam for a RIPE meeting. On Friday morning I gave a lightning talk called where does my computer get the time from? The RIPE meeting website has a copy of my slides and a video of the talk; this is a blogified version, not an exact transcript.
they look after a lot of different top secret satellites and other stuff at Schriever, as you can see from all the mission logos
When I was preparing this talk I noticed on Apple Maps that there’s a huge building site in the middle of the USNO campus. It turns out they are building a fancy new clock house; the main limit on the accuracy of their clocks is environmental stability: temperature, humidity, etc. so the new building will have serious air handling.
twice a year the IERS sends out Bulletin C, which says whether or not there will be a leap second in six months time; leap seconds are added (or maybe removed) from UTC to keep it in sync with earth rotation
for example, you can subscribe to IERS Bulletin A, which is a weekly notice with precise details of the earth orientation parameters