Clifford D. Simak entitled a science fiction book Time is the Simplest Thing
Unfortunately, in the realm of science reality, time turns out to be not simple at all. Indeed, it turns out to be even political, even to the point of a conflict between universal time and our observations of the universe.
Harper's Magazine has an interesting article with a rather dramatic title: "Clash of the Time Lords" (December 2006, page 46). Unfortunately it is subscribers-only.
It describes a conflict between the computer time people, some of whom would like our atomic time to tick along without any adjustments, and the astronomical time people, who benefit from having leap seconds inserted into the time stream, so that measured time accords with the Earth and the Sky.
To make things even more complicated, some computer-based systems already ignore the leap seconds. For example, GPS time is ahead of Coordinated Universal Time (UTC) by 14 seconds. GPS time has no timezones, it is a single, fixed, world-wide time.
leapsecond.com has a nice Java-based clock that shows the different time "standards" - but it relies on your local computer clock to be correct
Assuming you have a newer operating system with network time feature enabled, your computer's clock is probably quite close to UTC (+/- timezone offset), whether directly from a national time agency like NIST or NRC, or indirectly through secondary time servers.
You can also see the official times directly on the web, e.g.
This raises a question of synchronizing one's camera with the correct time, for the purposes of GPS location matching by timestamp. Should one sync to UTC or GPS time? Are there any cameras that even keep time to within 14 seconds?
Why can't our cameras just get their locations and times directly from internal or external GPS units, without this roundabout method of capturing two separate files (photo and track log) and later matching them? Or why can't my camera ask my phone what time it is? (I assume the cell phone provider is sending me updates with accurate UTC time and offsets.)