As seen in Figure 4, the position of the Sun moves with respect to the stars because of the Earth's orbit around it. By definition, that passage is called local noon. However, when that same position relative to the stars crosses our meridian on the following day, the Sun will not yet have reached our meridian. That is to say, the position will cross our meridian before local noon. The interval of time between two successive meridian crossings of a fixed position in inertial space is referred to as one sidereal day .
Sidereal midnight occurs when the vernal equinox crosses the meridian.
The interval of time between two successive meridian crossings of the mean sun is referred to as one mean solar day. As seen in Figure 4, the Earth must rotate a bit more for a mean solar day than for a sidereal day. This difference, while small, is extremely important. Unfortunately, this approach requires a table of reference times to do the calculations. While we've covered a lot of ground in this column, we obviously still have a bit more to go before we can answer the questions raised above.