Which of the following values is never exceeded by the equation of time?

• A. 00 hr 16.5 min
• B. 01 hr 23.0 min
• C. 00 hr 40.0 min
• D. 02 hr 15.0 min

Answer: (A)

The equation of time is the difference between apparent solar time (sundial time) and mean solar time (clock time). It changes during the year because Earth’s orbit is eccentric and tilted, so the length of days according to the Sun isn’t constant. In practice, this difference stays within a fairly small range, roughly from -14 minutes to about +16.5 minutes over the year. That means the largest amount by which sundial time can lead or lag behind clock time is about 16 minutes 30 seconds. Therefore, a bound of 00 hr 16.5 min is the upper limit the equation of time can reach but not exceed. The other values—well over an hour—are far beyond what the equation of time can produce, so they are not exceeded by it.