When the Earth orbits around the sun, relatively speaking, does it circle in the same path each time?

Question

When the Earth orbits around the sun, relatively speaking, does it circle in the same path each time?

In: 184

Answer 1

Not at all.

I know you asked about the Earth’s orbits relative to the Sun, but it’s important to note the Sun is moving in the galaxy, and the galaxy is moving through the void, so the Earth’s motion could almost be better compared to a squiggly line than a circle, depending on your point of view.

First off, the Moon has gravity and it tugs on the Earth, so at the very least that tug would make the line of any orbit wriggle. The other planets also tug on the Earth, and although their influence is resonant (meaning, it’s a stable ratio), it does matter and also wriggles the Earth’s orbit.

Anyway, Earth’s orbit isn’t circular, it’s very slightly elliptical, meaning there is a part of the orbit closer to the sun and a part of the orbit farther from the sun, shaped kind of like an egg, but it’s pretty close to a circle so we usually show it like that on pictures. The influence of the Moon and planets tugging on the Earth means it’s not a perfect ellipsis either, so the egg shaped orbit rotates year by year, meaning the Earth won’t be in exactly the same place this time next year. It’s kind of like a Spirograph.

Earth’s orbit also isn’t “flat”, in the sense that the ellipsis is slightly tilted relative to the earth’s axis, the sun’s axis, and the solar systems axis. The tilt also changes over a period of tens of thousands of years, varying up and down, partly accounting for imperfections in the resonant orbits of other planets and the Moon, like a wobbling top or gyroscope. Space is 3D after all.

So, you could say the Earth’s orbit wriggles and swirls up and down and in and out as it goes round and round the Sun.

The result is, currently, the southern hemisphere gets more light from the sun in summer than the northern hemisphere gets in summer, while the northern hemisphere gets more sun in winter than the south does. This wouldn’t happen if Earth’s orbit was perfectly circular and flat. Because northern summers are cooler, northern snow wouldn’t melt as much in the mountains, and warmer winters also mean more snowfall in the north, so it’s believed that the tilt and ellipsis cycles are key to the growth of glaciers and the Earth’s ice ages. In fact, there’s some evidence that we’d be in the beginnings of an ice age right now if it wasn’t for human-driven global warming.