The equation of time is 8m 40s. The apparent Sun is ahead of the mean Sun. If you are on the central meridian of your time zone, the apparent Sun will cross your meridian at what time?
• Equation of time and how it relates apparent (true) Sun to mean Sun • What it means physically when the apparent Sun is ahead of the mean Sun • On the central meridian of a time zone, when the mean Sun is on the meridian
• First decide: when does the mean Sun cross your meridian in zone time when you are on the central meridian? • If the apparent Sun is ahead of the mean Sun by 8m 40s, does that make its meridian passage earlier or later than the mean Sun’s? By how much? • Translate the sign of the equation of time into a clock correction: do you add or subtract 8m 40s from 12-00-00 ZT?
• Be sure you know that on the central meridian, local mean time (LMT) at meridian passage is 12-00-00 ZT for the mean Sun • Check the sign convention for equation of time: is it defined as apparent minus mean, or mean minus apparent, in your Nautical Almanac? • Verify whether an apparent Sun ahead means upper transit occurs before or after noon mean time and adjust the 12-00-00 ZT accordingly by 8m 40s
No comments yet
Be the first to share your thoughts!