The equation of time relates Local Apparent Time to Local Mean Time by which quantity?

• A. The sum of Local Apparent Time and Local Mean Time
• B. The product of Local Apparent Time and Local Mean Time
• C. The difference between Local Apparent Time and Local Mean Time
• D. The ratio of Local Apparent Time to Local Mean Time

Answer: (C)

The key idea is that actual solar time and mean clock time don’t run in perfect sync all year. Local Apparent Time is based on the Sun’s true position, while Local Mean Time uses a fictitious Sun that moves at a constant rate. The equation of time is simply their difference: Local Apparent Time minus Local Mean Time. This difference can be positive or negative and varies through the year because of the Earth’s elliptical orbit and the tilt of its axis, roughly ranging from about -14 to +16 minutes.