At sunset

The time of sunrise and sunset changes constantly throughout the year. Even on the same day, the sunrise and sunset times at different latitudes are different. The earliest sunrise is before summer solstice, the latest sunset is after summer solstice, the earliest sunset is before winter solstice, and the latest sunrise is after winter solstice. It contains some ingenious principles of sphere geometry, kinematics and celestial mechanics.

The time of sunset will change with the seasons and latitudes in different places. Traditionally, in the northern hemisphere, the sunset time is the earliest from winter to Sunday, and the sunset time is the latest from summer to Sunday.

But in fact, the earliest time of sunset should be 65438+early February, and the latest time of sunset should be the end of June. Even in the equatorial region, the time of sunrise and sunset will change a little during the year. These changes can be represented by daily trajectories.

When the sun below the horizon is close to the horizon, it has been highly deflected, which makes us stand on the earth and observe that when the geometric center of the sun is just above the horizon, the real sun is about 0.6 below the horizon.

This will advance the sunrise time in most parts of the earth by about 3-4 minutes, and postpone the sunset time by about 3-4 minutes. The influence of these two reasons is about 7 minutes. For example, the spring equinox in Guangzhou is 6: 3 1, the sunset 18: 38, the autumn equinox is 6: 16, and the sun sets 18: 23.