Perihelion, Aphelion and the Solstices
Perihelion, Aphelion and the Solstices

Perihelion, Aphelion and the Solstices

The word “perihelion” comes from the Ancient Greek words “peri”, meaning “near”, and “helios”, meaning “the Sun”. “Aphelion” derives from the words “apo”, meaning “away”, and “helios”, meaning “the Sun”.

The perihelion is the point in the orbit of the earth where it is nearest to its orbital focus, to the sun. It’s the opposite of aphelion, which is the point in the orbit where the earth is farthest from its focus.

The word solstice is derived from the Latin “sol” meaning “sun” and “sistere” meaning “to stand still”. During the solstices, the Sun appears to stand still in declination. The seasonal movement of the Sun’s path, as seen from Earth, comes to a stop before reversing direction.

Is the Winter Solstice and the Perihelion Eelated?

Earth moves closest to the sun on January 4, 2017, at around 9:17 am EST. This event is called the Earth’s Perihelion. Meanwhile, the December Solstice took place on December 21 at 3:44 AM EST.

At the Perihelion in January the Earth is 91 million miles from the sun. In contrast, it is 94 million miles away on the July Aphelion. During the winter solstice, the Earth’s Southern Hemisphere is tilted most toward the sun and its mid-summer in the southern hemisphere.

The date of Earth’s perihelion drifts back as the centuries pass. These two astronomical events are separated by about two weeks for us now. A few centuries ago they were closer together and in fact, they happened in 1246 AD. As time passes, these events will drift even farther apart.

On the average, one revolution of the Earth relative to perihelion is about 25 minutes longer than one revolution relative to the winter solstice. The perihelion advances one full calendar date every 60 years.

As the Earth’s perihelion progress, the alignment will happen at the same time as the March equinox in 6430 AD.

What Causes Seasons on Earth?

Seasons occur because Earth’s axis is tilted at an angle of 23.4 degrees and different parts of Earth receive more solar energy than others. Because of Earth’s axial tilt (obliquity), our planet orbits the Sun on a slant. This means different areas of Earth point toward or away from the Sun at different times of the year.

Opposite Seasons

When the Northern Hemisphere points towards the Sun, the Southern Hemisphere is pointing away from the Sun.

In the Northern Hemisphere this creates summer during the months of June, July, and August. Then winter in December, January, and February, when the North Pole is tilted toward the Sun. The Southern Hemisphere is then tilted away.

In the Southern Hemisphere, this creates winter during the months of June, July, and August. Then summer in December, January, and February. The South Pole is tilted toward the Sun and the Northern Hemisphere has tilted away.

Distance Does Not Cause Seasons

It is a common misconception that seasons occur because of Earth’s elliptical orbit around the Sun, with winter occurring when Earth is farthest away from the Sun, and summer when it is closest to it.

Our planet’s distance from the Sun has little effect on the onset of seasons. In fact, Earth is closest to the Sun, or at its Perihelion, around the Northern Hemisphere’s winter solstice, while it is farthest away from the Sun, or at its Aphelion, around the north’s summer solstice.

The Dread Pirate Dave

David is the Editor in Chief of Postcards From the Edge. I was born on a cold November morning on the showy plains of Colorado. Like my father, before me, I am an American Nomad.

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