On January 4th, 2025 at 8:28 a.m. EST, Earth will reach perihelion, the point in its orbit when it is closest to the sun. Then why is it so cold, at least in the northern hemisphere?
Winter—indeed all seasons—don’t depend on the distance from the sun. If they did, then Australia would celebrate the Christmas season with snow instead of visits to the beach. Seasons are due to the axial tilt of the earth relative to its orbit. Throughout the year, the sun appears lower or higher in the sky, and the hours of daylight are shorter or longer.
https://www.timeforkids.com/wp-content/uploads/2022/07/K1_220902_backpage_seasons.jpg?w=1024
At that moment on the 4th, Earth will be 91,405,993 miles away from the sun. Six months later on July 3rd at aphelion, it will be 94,502,939 miles away. The earth’s orbit only varies by plus or minus 1.7% from an average value. Yes, it’s elliptical and not circular, but not by much!
An interesting contrast arises on Mars, whose orbit is much more elliptical, varying by 9% from the average. Combined with Mars’s axial tilt (very similar to Earth’s), this makes seasons in Mars’s southern hemisphere rather extreme. When it is summer there, Mars is at perihelion, making it warmer. And when it is winter in the south of Mars, the planet is farthest from the sun at aphelion, making it even colder.
https://www.britannica.com/place/Mars-planet/Basic-astronomical-data#/media/1/366330/70791
We should note that “warm” on Mars means a maximum of 68°F (20°C) at noontime on the equator. With an extremely thin atmosphere, temperatures plummet to -100°F (-73°C) once the sun goes down.
We should be grateful for many aspects of the Earth’s orbit for our relatively mild diurnal and seasonal variations!