Tropic of Capricorn
What is the Tropic of Capricorn?
It is the circle at 23.4° south — the southern twin of the Tropic of Cancer. The Sun stands straight overhead there once a year, on the December solstice, and never south of it.
The same limit, going south
Whatever the Tropic of Cancer is for the north, the Tropic of Capricorn is for the south. Earth’s axis leans about 23.4°. That lean never grows, so the Sun’s overhead point never crosses either tropic.
Between the two tropics, every place gets the Sun straight up on two days each year — once on the way north, once on the way back. Outside them, a vertical pole always casts some noon shadow, even on the longest day.
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December, not a different Earth
Nothing about Earth changes between June and December except which end of the axis leans toward the light. When it is summer in Chile it is winter in Canada, on the same planet, at the same distance from the Sun. Distance is not the season.
The name Capricorn is the same kind of fossil as Cancer: the December-solstice Sun used to stand in that constellation. Precession moved the stars. The latitude stayed with the tilt.