Earth was at perihelion on Jan. 4; what the heck is it, and when does it occur?

JACKSONVILLE, Fla. -- – Wednesday was a big day if you live on planet Earth.

Perihelion occurred on Jan. 4. What exactly is that, you might ask?

Perihelion is the point at which an orbiting body (in this case, the Earth) is at its closest point to the sun.

But why does this happen? And how can it happen in the coldest month of the year?

Earth’s elliptical orbit

The term perihelion is Greek, and it means around (peri) the sun (Helios).

It is the result of the elliptical orbit Earth has around the sun.

All planets, and even comets and asteroids, have elliptical orbits around our large sun.

These oval orbits create days where the Earth is closer to the sun than other days.

Perihelion always occurs in early January, but it is not on one specific date as the Julian calendar does line up exactly with Earth’s orbit (why we have leap days every four years).

And the sun is larger in the sky, but not by much. The sun is only about 3% larger in early January.

At perihelion, Earth is a close 91 million miles away from the sun.

How can we be so close in January?

So, how can be Earth be the closest to the warm sun in normally the coldest month of the year?

Our seasons are not governed by the location of Earth relative to the sun. It’s governed by the tilt of the Earth.

In January, the northern hemisphere is tilted away from the sun. This creates winter.

Because of the seasonal lag that occurs, January is normally the coldest month as the reduction of sunlight from the sun creates colder conditions.

This is despite the fact the planet is closer to the sun than during the summer months.

Moving away

We now begin to orbit further away from the sun as the weeks and months progress.

There is a day when the Earth will be furthest away from the sun. This is called aphelion and it occurs in July.

Again, because of the tilt of the Earth, July is normally one of the warmest months despite the further distance from the sun.

So we start the year the closest to the sun we will be, despite being in the heart of the winter season.