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When is Sunrise?

The time of sunrise will vary with the season and the latitude of each place. Traditionally, it is believed that in the northern hemisphere, the winter solstice has the latest sunrise time, but in fact, the latest sunrise time should be early January. For the same reason, the earliest time of sunrise is not at the summer solstice but in mid-June. Even in the equatorial region, the time of sunrise and sunset will change slightly throughout the year.

In fact, for most areas on the earth except the equator and the poles and their vicinity, the earliest day of sunrise of the year is before the summer solstice, the latest day of sunset is after the summer solstice, and the earliest day of the evening is before the winter solstice. The latest day of sunrise is after the winter solstice. Do you know why?

When is Sunrise?

First, the earth revolves around the sun from west to east at all times. According to the relativity of motion, we can also observe from the world that the sun revolves around the celestial ecliptic from west to east in a year. Since the earth’s rotation angle of inclination of the axis, the great circles of the sun on the ecliptic earth’s celestial equator areare inclined when the sun is at the two points.

There will be an angle when crossing the equator. The velocity component parallels the equatorial Less than the annual average speed; when the sun is at the solstice, its direction of motion is entirely parallel to the equator, so the rate is higher than the annual average speed. This will cause the day’s daylight hours to be gradually advanced around the vernal and autumnal equinoxes; daylight hours are steadily delayed around the summer and winter solstices.

Secondly, we know that the earth’s orbit is an ellipse rather than a perfect circle, and the sun is at a focal point of the planet’s orbit. According to Kepler’s law, the speed will increase when the earth approaches the sun, and the rate will be the fastest when it reaches the perihelion.


It will slow down when it is far away, and the speed will be the slowest for the aphelion. This effect can also be reflected in the annual trajectory of the sun on the celestial equator. Although the second factor has a more minor impact than the first factor, it is also sufficient to delay the daylight hours of the vernal equinox in the northern hemisphere by about 16 minutes compared to the vernal equinox. Specifically, if the spring equinox in a place is sunrise at 6:19 and sunset at 18:19, the autumnal equinox will be at 6:03 and evening at 18:03.

Suppose the influence of atmospheric refraction is taken into account when the sun is near the horizon. In that case, the apparent position will be higher than the actual position. I am making the sunrise about 3 to 4 minutes earlier and delaying the sunset about 3 to 4 minutes. Minute. The impact of these two reasons reaches approximately 7 minutes—for example, Guangzhou vernal equinox sunrise at 6:31. And sunset at 18:38, then the autumnal equinox sunrise at 6:16, and evening at 18:23.


The time of sunrise and sunset can be calculated by tracking the sun’s trajectory. Still, the estimated time will be slightly different than the real sense. The calculated sunshine time will be longer than the real sense. And the computed time The time of the night is shorter than it feels.

Because sunlight affected by the earth’s atmosphere and refracted, people have already seen the sunrise scenery when the sun has not risen to the horizon. An illusion produce every day at sunrise. Ancient Chinese astronomers once recorded a rare astronomical phenomenon called ” Tian Zaidan, “which means two lights on the same day. This is usually due to the astronomical spectacle caused by the total solar eclipse from five to seven in the morning. When the first sunrise, the sky gradually darkens and then greets the second sunrise.

As we all know, the time of sunrise is constantly changing throughout the year. Even on the same day, the sunrise times at different latitudes are different. So why does it cause this effect? According to the relativity of motion, the earth revolves around the sun from west to east all the time. We can also observe from the world that the sun rotates around the celestial ecliptic from west to east in a year. This will naturally cause the sun’s right ascension and declination to change all the time. And in different seasons, the speed of change is slightly different. Which causes the sunrise time during the year to change continuously with the seasons.

Also read: what do ducks eat.



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