Winter Solstice
We often think of the winter solstice as an event that spans an entire calendar day, but the solstice actually lasts only a moment. Specifically, it’s the exact moment when a hemisphere is tilted as far away from the Sun as it can be
The farthest points from the equator where the Sun can appear directly overhead are referred to as the tropics. The tropics are lines of latitude that circle the Earth above and below the equator, at about 23.4 degrees north and south. This angle is set by Earth’s axial tilt.
There are two moments each year when one of Earth’s poles is tilted the most toward the Sun, and the Sun lies directly above one of the tropics. These moments are the solstices:
- The June solstice takes place sometime between June 20 and 22, when the Sun is directly above the Tropic of Cancer in the Northern Hemisphere. As a rough guide, the Tropic of Cancer passes through Mexico, northern Africa, the Middle East, India, and China.
- The December solstice happens sometime between December 20 and 23, when the Sun is directly over the Tropic of Capricorn in the Southern Hemisphere. In brief, the Tropic of Capricorn runs through South America, southern Africa, and Australia.
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What is a Solstice?
A solstice is one of the two times of the year when the positioning and tilt of Earth relative to the sun results in the most amount of daylight time or the least amount of daylight time in a single day. There are two solstices during the year: one that occurs around June 20–22 (usually June 20 or 21) and one that occurs around December 20–23 (usually December 21 or 22).
The solstices are traditionally considered to mark the start of summer and winter. But which season begins with each solstice depends on which hemisphere you’re in. In the Northern Hemisphere, the summer solstice occurs in June and the winter solstice occurs in December. In the Southern Hemisphere, it’s the opposite. The summer solstice results in the longest day of the year, meaning it has the most time of daylight, and the winter solstice results in the shortest day of the year, meaning it has the longest period of darkness.
In contrast, an equinox is one of the two times of the year when the amount of daylight and nighttime hours are just about of equal length. The two equinoxes occur around March 20–21 and September 22–23. In the Northern Hemisphere, the vernal equinox (or spring equinox) occurs in March and the autumnal equinox occurs in September. In the Southern Hemisphere, it’s the opposite.
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