Monthly Archives: January 2018

Happy New Year 2018! Happy Perihelion!

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Earth and sun via ISS Expedition 13/ NASA

Greetings of the New Year to All!

We on Earth have only a few weeks ago observed our December Solstice, when days are shortest in the Northern Hemisphere and longest in the Southern. It was the time of the New Year for indigenous people around the world. Now, we are celebrating the conventional New Year for our times at the beginning of the Western calendar in January.

Did you know that, on January 2 and 3, Earth will be closest to the Sun in our orbit around the Sun? This is always true around this time in our history. EarthSky writes:

On January 3, 2018, Earth at its closest point swings to within 91,401,983 miles (147,097,233 km) of the sun. That’s in contrast to six months from now, when the Earth reaches aphelion – its most distant point – on July 6, 2018. Then we’ll be 94,507,803 miles (152,095,566 km) from the sun.

In other words, Earth is about 3 million miles (5 million km) closer to the sun in early January than it is in early July. That’s always the case. Earth is closest to the sun every year in early January, when it’s winter for the Northern Hemisphere.

Do you wonder if the solstice and the perihelion, the closest approach of Earth to Sun, are related? This is not always true, because the dates change in the course of centuries. In fact, in the year 1246, both occurred on the same day. We are living in very interesting times…

Here’s the explanation from EarthSky.

Earth comes closest to the sun on January 3, 2018 at around 5:35 UTC; translate to your time zone. This event is called Earth’s perihelion. Meanwhile, the December solstice took place on December 21, 2017. At perihelion in January, Earth swings to within about 91 million miles (147 million km) of the sun. That’s in contrast to six months from now, when we’ll be about 94 million miles (152 million km) from the sun. At the December solstice, Earth’s Southern Hemisphere is tilted most toward the sun; it’s the height of summer in that hemisphere. Are the December solstice and January perihelion related? No. It’s just a coincidence that they come so close together.

The date of Earth’s perihelion drifts as the centuries pass. These two astronomical events are separated by about two weeks for us. But they were closer a few centuries ago – and in fact happened at the same time in 1246 AD.

As the centuries continue to pass, 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 December solstice. Perihelion advances one full calendar date every 60 or so years.

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