# Why does earth's distance from the sun change?

Jan 21, 2016

The Earth's orbit around Sun is under a central force that is inversely proportional to square of distance from Sun.The orbit is not a circle but an ellipse with Sun at one focus.

#### Explanation:

The distance $r$ changes according to the formula
$\frac{l}{r} = 1 + e \cos \left(\theta\right)$
where $e$ is the eccentricity of the ellipse,
l = (("minimum distance")("maximum distance"))/("semi major axis of the ellipse").
$\theta$ is the inclination of Sun-Earth radius to least-distance radius.

Jan 26, 2016

Thanks for the depiction. The Sun's distance CS = ae from center C is 1 in 60 of the semi-major a. So, for orbit on an A4 paper, S will be quite close to C.

#### Explanation:

e = 0.01671. CS/a = 0.01671. Also, minor axis b is 0.99986a. If the orbit is drawn to scale on A4 paper, it will appear as a circle. Of course, some elongation is necessary to show what it is, an ellipse.