And the answer: Perihelion.
When the Earth is at its perihelion, it is at its closest distance to the Sun, about 147.5 million kilometers away. This time occurs about two weeks after the December solstice each year. The term is derived from Ancient Greek, in which "helios" means "Sun," and "peri" means "close."
As the Earth travels around the Sun, there are points during which we reach the farthest distance from the sun’s rays, or the closest. Interestingly, Earth reaches its perihelion—the closest point to the Sun—during some of the coldest days of the year for the Northern Hemisphere. This is due to the fact that our proximity to the Sun doesn’t determine the weather or the seasons: it’s actually the tilt of the Earth on its axis that makes winter months cold and summer months hot.
Earth isn’t the only planet with a perihelion or aphelion—every planet in our solar system has a closest or furthest point from the Sun as they complete a revolution around it each year. Earth’s orbit is elliptical, meaning it’s not a perfect circle and much more of an elongated oval, yet other planets have varying degrees of extremity in their orbital paths. Mars, for example, has a much more elliptical orbit than Earth. In comparison, Earth’s orbit seems almost circular, which may also account for how Earth’s climate can maintain relative stability despite seasonal variations.
When Earth is closer to the Sun, the star’s gravitational pull is slightly stronger, causing our planet to travel just a bit faster in its orbit. For those of us in the Northern Hemisphere, this results in a shorter fall and winter, since we are moving faster through space during that time of the year. On the other hand, when Earth is farthest from the Sun, it travels more slowly, resulting in a longer spring and summer. So while it may feel like the bitter cold of January and February drag on forever, you can take solace in the fact that the Earth is moving as quick as it can to get us to warmer months.
Did you know?
Yesterday, the Earth reached perihelion! Also known simply as Perihelion Day, Earth’s perihelion can be observed by simply looking up—as it is the day in which the sun appears the largest in the sky. Although 91 million miles away feels like a lot, it’s the closest we’ll ever get to the Sun on our orbital path (and thank goodness for that!)
Learn more about Earth’s perihelion and aphelion here.