The December solstice occurs just a few weeks before Earth reaches its perihelion – the point in our world’s orbit in which we are closest to the sun – each year. December solstice comes around December 21. Perihelion comes in early January. At perihelion in January, Earth is about 147 million kilometers from the sun, in contrast to about 152 million kilometers in July.
Earth will be closest to the sun in 2011 on January 3
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.
Image Credit: Wikimedia Commons/ Dennis Nilsson
Does the perihelion effect the weather in the southern hemisphere since the earth is tilted closer to the sun at the December solstice?
Tiffany, I’m not sure. Distance is just one factor. There are many complicated variables at work.
For example, the length of the seasons is a bit different in each hemisphere. That’s because we’re at perihelion in northern hemisphere winter, and therefore moving fastest in orbit around that time. So are fewer days between the December solstice and the March equinox than between the June solstice and September equinox – in other words, winter is a few days shorter in the northern hemisphere.
But I think a more important variable might be the ratio of land to water in each hemisphere, which would have a big effect in moderating temperatures.
We’ll look into it! Thanks for visiting.
- ES
I do not get it. What causes our fairly stable orbit around the sun to slow down and change the perihelion date every 60 years?