What causes the seasons on Earth?

Earth has seasons because its rotational axis is tilted by about 23.5 degrees relative to its orbit around the Sun. Because of the tilt, some parts of the globe lean toward the Sun while others lean away, which changes how much sunlight reaches each region over the year. The result is the yearly cycle of seasons, as explained by [weather.metoffice.gov.uk](https://weather.metoffice.gov.uk/learn-about/weather/seasons) and [nesdis.noaa.gov](https://www.nesdis.noaa.gov/about/k-12-education/understanding-our-planet/why-does-earth-have-seasons). [1] [2]

As Earth orbits the Sun, its axis keeps pointing in the same direction. That means the North Pole tilts toward the Sun around June and the South Pole tilts toward it around December. The Northern Hemisphere has summer in June because the Sun's rays strike it more directly then than at any other time of year, and winter in December when the South Pole has its turn tilted toward the Sun, according to [spaceplace.nasa.gov](https://spaceplace.nasa.gov/seasons/). The Southern Hemisphere experiences the reverse. [3]

The National Weather Service describes the key dates. The solstices, near June 21 and December 21, are when the axis points most toward or away from the Sun. At the equinoxes, near March 21 and September 21, the axis points 90 degrees away from the Sun's direction, and day and night are each about 12 hours everywhere, per [weather.gov](https://www.weather.gov/lmk/seasons). Around the June solstice the Sun is directly over the Tropic of Cancer, and around the December solstice it is over the Tropic of Capricorn, as noted by [weather.gov](https://www.weather.gov/fsd/season). [4] [5]

When the Sun is high in the sky, light falls more directly, so more light and heat reach each square centimeter of ground. When the Sun is lower, the same light spreads over a larger area and delivers less heat per unit of ground, according to [weather.gov](https://www.weather.gov/lmk/seasons). A high Sun also means sunlight crosses less atmosphere, so less is scattered before reaching the surface, and it comes with longer days, as described by [weather.gov](https://www.weather.gov/fsd/season). Britannica Kids adds that regions near the Equator get steadier sunlight year-round, so their seasonal variation is smaller, while higher latitudes see more pronounced changes ([kids.britannica.com](https://kids.britannica.com/scholars/article/Why-Do-We-Have-Seasons/650223)). [4] [5] [6]

Many people believe summer happens because Earth is closer to the Sun. This is incorrect. Earth's orbit is slightly elongated, but in the Northern Hemisphere winter occurs when Earth is closest to the Sun and summer when it is farthest, per [nesdis.noaa.gov](https://www.nesdis.noaa.gov/about/k-12-education/understanding-our-planet/why-does-earth-have-seasons). The closest point, perihelion, falls in January and the farthest, aphelion, in July, but the difference is not large enough to substantially affect climate, according to [weather.gov](https://www.weather.gov/fsd/season). If distance were the cause, the whole planet would be warmest at the same time, rather than the hemispheres having opposite seasons. [2] [5]

NASA's Space Place says that long ago, when Earth was young, something big is thought to have hit it and knocked it off-kilter, so it leans rather than rotating with its axis straight up and down ([spaceplace.nasa.gov](https://spaceplace.nasa.gov/seasons/)). The source presents this as what is thought, not as settled fact. The tilt also varies somewhat over time, from near 22 degrees to about 24.5 degrees, according to [weather.gov](https://www.weather.gov/fsd/season). [3] [5]