When the Earth orbits around the sun, relatively speaking, does it circle in the same path each time?
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Relative to the sun it very roughly does but the closer you look, the more you see slight differences:
* The earth doesn’t orbit in a perfect circle but in an elliptical (oval) shape. The point where it’s nearest the sun rotates a little each year, taking 108 000 years to make a complete circuit; the oval shape is itself revolving. Put another way, the time the earth is nearest the sun is almost 5 minutes later each year. Also, the shape of the orbit changes over time, sometimes being more circular and others more oval-shaped.
* The earth’s orbit is almost perfectly flat but it isn’t lined up exactly with the orientation of the sun’s rotation on its axis. The plane of the earth’s orbit also revolves around the sun in a 7110-year cycle.
* The moon has an effect on the position of the earth. It’s really the centre of mass of the earth and the moon that orbits the sun; the earth and the moon in turn orbit that centre of mass. Since there are 12.4 months per year—not a whole number—the earth is in a different offset from the centre of mass at the start of every year.
* The other planets in the solar system also exert forces on the earth that change its orbit slightly, although these are relatively minor (because the planets are very distant and much less massive than the sun).
The concept of circular and elliptical orbits is only an approximation to our reality; it’s a simplification assuming there are only two spherical bodies. Even in an ideal two-body case, relativistic effects as theorised by Einstein would cause some gradual changes.
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