Of course, we now know that the Sun isn’t orbiting the Earth; sunrise happens because the Earth is rotating on its axis. Once every 24 hours, each spot on the Earth turns to face our star, and gets its chance to see the Sun rise. And then at the end of the day, the rotation of the Earth brings the sun to the other horizon, and the sunset.
Astronomers calculate sunrise as the instant when the upper edge of the Sun first appears on the horizon in the morning. Since the Sun is actually a circle, it can take a few minutes for its entire circle to pass above the horizon.
Sunrise always happens in the East, and then the Sun makes a westward journey across the skies, and finally setting in the West. The appears to make this motion because the Earth is actually rotating counter-clockwise when viewed from above the North Pole.
The time of sunrise depends on the time of year, and your distance (north or south) away from the equator. Since time zones can be quite large, the precise moment of your local sunrise depends on your position within that time zone. In other words, local times for sunrise will be different for every spot on Earth.
The time of the year has one of the biggest impacts on sunrise time. Since the Earth’s axis is tilted, it’s angle towards the Sun changes over the course of the year. The winter solstice occurs around December 21, and it’s the time when the Sun is lowest in the horizon for the northern horizon – the sunrise is the latest, and the days are shortest. The summer solstice occurs on June 21, and it’s the opposite situation: the sun rises at its earliest, and the days are longest.
The equinoxes are times in the year when the sunrise is 12 hours away from the sunset; the day and night are the same length of time. The spring equinox usually occurs around March 20th, and the autumn equinox happens around September 23rd every year.
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