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Earth's orbit: 299.2 million km [b] 2 AU [c] 2.99×10 8: The average diameter of the orbit of the Earth relative to the Sun. Encompasses the Sun, Mercury and Venus. [18] Inner Solar System ~6.54 AU 9.78×10 8: Encompasses the Sun, the inner planets (Mercury, Venus, Earth, Mars) and the asteroid belt.
Earth's rotation axis moves with respect to the fixed stars (inertial space); the components of this motion are precession and nutation. It also moves with respect to Earth's crust; this is called polar motion. Precession is a rotation of Earth's rotation axis, caused primarily by external torques from the gravity of the Sun, Moon and other bodies.
The curvature of the Earth is evident in the horizon across the image, and the bases of the buildings on the far shore are below that horizon and hidden by the sea. The simplest model for the shape of the entire Earth is a sphere. The Earth's radius is the distance from Earth's center to its surface, about 6,371 km (3,959 mi). While "radius ...
Due to the very slow pole motion of the Earth, the Celestial Ephemeris Pole (CEP, or celestial pole) does not stay still on the surface of the Earth.The Celestial Ephemeris Pole is calculated from observation data, and is averaged, so it differs from the instantaneous rotation axis by quasi-diurnal terms, which are as small as under 0.01" (see [6]).
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Ignoring the influence of other Solar System bodies, Earth's orbit, also called Earth's revolution, is an ellipse with the Earth–Sun barycenter as one focus with a current eccentricity of 0.0167. Since this value is close to zero, the center of the orbit is relatively close to the center of the Sun (relative to the size of the orbit).
Trying to illustrate two conflicting ideas in a drawing presented as representing one of those two ideas is counter-productive to the use of a drawing to help clarify the point. I would add that it’s not clear to say that “The ecliptic is the apparent path of the Sun on the celestial sphere.”
The images at right attempt to explain the relation between the precession of the Earth's axis and the shift in the equinoxes. These images show the position of the Earth's axis on the celestial sphere, a fictitious sphere which places the stars according to their position as seen from Earth, regardless of their actual distance. The first image ...