January 3 - closest point to the sun, can you believe it?
d ~ 18'009'600 km: day 7
You might ask why we chose January 3rd to begin filming. Well believe it or not, it's a very special day. Despite the freezing weather we are getting at the moment, the Earth is at its closest point to the sun it will get all year. It's called Perihelion which is Greek for "near to the sun", and right now the Earth is 5 million kilometres closer to the sun than it will be in July, when it's at its furthest point.
Perihelion highlights how fascinating the relationship is between the earth and its cosmic star. Who would have thought that at the point when we are closest to the sun, we would experience such freezing temperatures? To kick-start our trip, 23 Degrees presenter Kate Humble and the production team visited Aonach Mor - one of the highest mountains in Scotland.
Perihelion is a result of the slightly strange shape of the Earth's orbit around the sun. It's not a perfect circle, it's an ellipse, and the sun isn't even in the centre, it's slightly off to one side. So at the moment we are just 147.1 million kilometres [91.4 million miles] from the sun. You are probably thinking - if we are closer, then why aren't we warmer? Well, our journey around the sun is complex and there's another factor that shapes our climate that is more powerful than just how close we are to the sun. And that's the tilt of the planet. Earth doesn't sit upright; it's tilted over to one side at an angle of 23.5 degrees.
The tilt and the Earth's motion around the sun create the seasons. In January the northern hemisphere is tilted away from the sun so the sunlight is spread more thinly over the northern half of the planet so we get our winter. Meanwhile the southern hemisphere which is now tilted towards the sun gets more sunlight and therefore enjoys summer. Gradually the Earth moves around the sun until July when the Northern hemisphere tilts towards the sun, when the reverse is true.
Now – in January – we are in midwinter, but the northern hemisphere is already starting its journey back towards the sun and over the next few months we will get more and more sunlight and slowly the Northern Hemisphere will rise from its slumber and move towards spring.