I know it was the coldest morning of the winter so far today but the earth will reach perihelion, a point in its orbit where it is closest to the sun.
This may strike you as odd, wouldn’t the earth always be the same distance from the sun? Well, it would if the earth traveled in a circular orbit. Instead, the earth travels around the sun in an ellipse.
So this means there is a farthest point too, called aphelion, which occurs in early July. The difference is about 5 million kilometers with perihelion around 147 million km and aphelion around 152 million km.
This amounts to about a 3.4% change. You wouldn’t normally notice this but it can be measured as in the included image shows.
This has nothing to due with the seasons which are caused by the earth’s 23.5 degree tilt. But you would think there would be some noticeable effect, after all it’s 5 million kilometers! It’s turns out there is an effect but it is small and just about masked out by the tilt and by changeable weather patterns.
Also, there is no relationship between perihelion and the winter solstice, which are presently separated by about two weeks. In fact, the two are drifting apart! In the year 1246 AD, they were coincident. Around 6000 AD, perihelion occur at the same time as the Vernal Equinox in March.
Crazy isn’t it? Milankovitch thought so too!