Perihelion Day: What to Know About Tonight’s Once-a-Year Sky Event

by Victoria Santiago
(Photo by NurPhoto/NurPhoto via Getty Images)

Today we’re at perihelion, which means we’re closer to the sun than we are any other day of the year. Wouldn’t you think it would be a little warmer outside, then? Unfortunately not, but there is one big benefit we get from this: winter in the northern hemisphere gets shorter. Not by much, but our winter is actually the shortest of the four seasons because of this. Winter is 89 days, which is short compared to summer’s 93 days. Summer, of course, is our longest season. The whole reason why we experience this odd phenomenon is because we travel around the sun in an oval shape, so our orbit is never completely even.

First thing this morning, the center of the Earth and the center of the sun will be 3% closer to each other than they are normally. Specifically, we’re only a mere 91,406,842 miles away from the sun. Just as we’re experiencing perihelion right now, there’s also a period of aphelion that happens during the summer. During that time, Earth is the furthest away from the sun that it can get.

It seems counterintuitive that we are closest to the sun right now, yet we’re in the middle of winter. The same goes for us being farthest from the sun during the warmer months. Even though we’re physically closer to the sun, our seasons are controlled by the axis upon which we rotate, instead of how close or far we are distance-wise. Thus, we have weaker sunlight and fewer hours of it, even though we’re technically closer.

The Perihelion Sliding Scale

Interestingly enough, this event gradually happens at different parts of the year. Because it involves the sun, perihelion seems like it would be a static event. However, over time the event moves throughout the year. While we’re experiencing it in January right now, that won’t always be the case. For example, in 13,000 years or so, perihelion will be happening in July. This affects aphelion as well, which would then happen in January.

Comets Get Close to the Sun, Too (And Have More to Show For It)

Of course, we aren’t the only mass floating around the solar system that is affected by perihelion. Other planets and objects experience perihelion, too. For example, Comet Leonard reached its closest point to the sun yesterday (1/3). Comets that get close to the sun are exceptionally pretty. Due to being directly exposed to the heat, the comets get bright blue and green lights in their tail.

For Comet Leonard, this is the last time it’ll reach perihelion in a long while. After it passes the sun, it will be flung out of our solar system for at least 80,000 years. We might not turn pretty colors when we get close to the sun, but at least we get to stay in orbit.