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| Astronomy Essentials | Space on Jan 03, 2015

Are the December solstice and January perihelion related?

December solstice 2014 is December 21. Earth is closest to the sun in 2015 on January 4. Coincidence?

Earth comes closest to the sun tomorrow – January 4, 2015 at 6:37 UTC (01:37 EST). This event is called Earth’s perihelion. Meanwhile, the December solstice took place on December 21. At perihelion in January, Earth is about 147 million kilometers from the sun, in contrast to about 152 million kilometers in July. At the 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.

Earth’s perihelion – or closest point to the sun – will happen at the same time as the March equinox in about 6000 AD.

Earth and sun via ISS Expedition 13 / NASA.

Earth and sun via ISS Expedition 13 / NASA.

Bottom line: December solstice 2014 is December 21. Earth is closest to the sun in 2015 on January 4. Despite their nearness in time, these two events are not related.

Earth closest to the sun on January 4, 2015

Everything you need to know: December solstice

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