Time – the fourth dimension
The environment is dynamic
- Therefore all attempts to designate locations need to take into account time
- We may choose to ignore time for application-specific reasons
- Yes, the “Prime Meridian” has moved, but should you care?
- When is time important; examples:
- Continental drift
- Geomagnetic polar drift
- Revolution around another body (e.g., the Sun)
- Rotation around an axis
To establish a system of time, one must define two quantities:
- The unit of duration (e.g., second or day), and
- The epoch, or the zero, of the chosen time