Many people assume Earth has seasons because we get closer to the Sun in summer and farther in winter. That’s a reasonable guess, but it’s wrong. In fact, Earth is slightly closer to the Sun in January (Northern Hemisphere winter) than in July. Distance from the Sun isn’t what makes summer and winter.
The real cause is Earth’s tilt. Our planet’s axis is tilted 23.5 degrees from vertical relative to its orbit. As Earth makes its yearly trip around the Sun, this tilt stays pointed in the same direction. For half the year, the Northern Hemisphere is tilted toward the Sun - meaning sunlight hits it more directly, days are longer, and it’s summer. The Southern Hemisphere is tilted away - meaning sunlight hits at a sharper angle, days are shorter, and it’s winter. Six months later, the opposite is true.
This is why the seasons in Australia are reversed from the US. Christmas in Sydney is during summer; in New York, it’s winter. Around the equator, the tilt has less effect, so equatorial countries don’t get pronounced seasons at all. Their year is more about wet versus dry periods than warm versus cold.
