Geocentric view of the seasons

Geocentric view of the seasons

·  Most places on Earth use a which is unequal to the local time, differing by up to an hour or even two hours, if (summer time) is included. In that case, the Sun could rise at 08:00 and set at 20:00, but there would still be 12 hours of daylight.

·  Even those people fortunate enough to have their time zone equal to the local time will not see sunrise and sunset at 06:00 and 18:00 respectively. This is due to the variable speed of the Earth in its orbit, and is described as the It has different values for the March and September equinoxes (+8 and −8 minutes respectively).

·  The above numbers are only true for the For this discrepancy increases (for example, 12 minutes in London) and closer to the Poles it gets very large. Up to about 100 km from either Pole, the Sun is up for a full 24 hours on an equinox day.

·  Height of the horizon on both the sunrise and sunset sides changes the day's length. Going up into the mountains will lengthen the day, while standing in a valley with hilltops on the east and the west can shorten the day significantly. This is why settlements in east-west running valleys are more favourable (daylight-wise) than north-south running valleys.

Sunrise and sunset are commonly defined for the upper limb of the solar disk, rather than its center. The upper limb is already up for at least one minute before the center appears, and likewise, the upper limb sets one minute later than the center of the solar disk. Due to the Sun, when near the horizon, appears a little more than its own diameter above the position than where it is in reality. This makes sunrise more than another two minutes earlier and sunset the equal amount later. These two effects add up to almost seven minutes, making the equinox day 12 h 7 min long and the night only 11 h 53 min. In addition to that, the night includes twilight. When dawn and dusk are added to the daytime instead, the day would be almost 13 hours.