You need to know that the Earth’s axis is not nicely aligned with the Earth’s orbit – it’s tilted from the vertical by about 23 degrees. So as the Earth moves around the Sun, one of the poles is leaning towards the Sun. For six months it’s the north pole, and for six months it’s the south pole (This affects how much sunlight each side of the world gets, and causes the seasons). The day of the year when each pole points closest to the Sun is called a solstice, and there’s one for each pole. These are traditionally called the Winter and Summer solstices, since they mark the astronomical beginnings of those months, but that’s confusing for people in the southern hemisphere (where everything is backwards). So I prefer to name them by the month in which they occur – the June and December solstices.
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